Today it is known that all living beings, Firstly, have a set of the same properties and consist of the same groups of biological polymers that perform certain functions; Secondly , the sequence of biochemical transformations that ensure metabolic processes is similar in them down to the details. For example, the breakdown of glucose, protein biosynthesis and other reactions occur almost identically in a variety of organisms. Consequently, the question of the origin of life comes down to how and under what conditions such a universal system of biochemical transformations arose.
Despite the common origin of the planets of the solar system, life appeared only on Earth and reached exceptional diversity. This is due to the fact that certain cosmic and planetary conditions are necessary for the emergence of life. Firstly , the mass of the planet should not be too large, since the energy of the atomic decay of natural radioactive substances can lead to overheating of the planet or radioactive contamination of the environment, incompatible with life; and too small planets cannot maintain an atmosphere around them, because their gravitational force is small. Secondly , the planet must rotate around the star in a circular or near-circular orbit, which allows it to constantly and evenly receive an extremely important amount of energy from it. Third , the intensity of the luminary's radiation must be constant; uneven flow of energy will hinder the emergence and development of life, since the existence of living organisms is possible within narrow temperature limits. All these conditions are satisfied by the Earth, on which about 4.6 billion years ago the conditions for the emergence of life began to be created.
At the initial stages of its history, the Earth was a hot planet. Due to rotation, with a gradual decrease in temperature, atoms of heavy elements moved to the center, and atoms of light elements (hydrogen, carbon, oxygen, nitrogen), from which the bodies of living organisms are composed, were concentrated in the surface layers. Metals and other oxidizable elements combined with oxygen, and there was no free oxygen in the Earth's atmosphere. Atmosphere consisted of free hydrogen and its compounds, i.e. was restorative in nature. According to A.I. Oparin, this served as an important prerequisite for the emergence of organic molecules by non-biological means. IN 1953 ᴦ. L.S. Miller experimentally proved the possibility of abiogenic synthesis of organic compounds from inorganic ones. By passing an electric charge through a mixture of H2, H2O, CH4 and NH3, he obtained a set of several amino acids and organic acids. Later it was found that in a similar way in the absence of oxygen Many organic compounds that are part of biological polymers (proteins, nucleic acids and polysaccharides) have been synthesized.
The possibility of abiogenic synthesis of organic compounds is confirmed by the fact that hydrogen cyanide, formaldehyde, formic acid, methyl and ethyl alcohols, etc. have been discovered in outer space.
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Fatty acids, sugars, and amino acids were found in some meteorites. All this indicates that quite complex organic compounds could have arisen under the conditions that existed on Earth 4.0-4.5 billion years ago.
More than 4 billion years ago, many volcanoes erupted with the release of huge amounts of hot lava, large volumes of steam were released, and lightning flashed. As the planet cooled, water vapor in the atmosphere condensed and rained down on the Earth, forming huge expanses of water. Since the surface of the Earth was hot at that time, the water evaporated, and then, cooling in the upper layers of the atmosphere, fell back onto the surface of the planet. This continued for many millions of years. Components of the atmosphere and various salts were dissolved in the waters of the primary ocean. At the same time, organic compounds - sugars, amino acids, nitrogenous bases, organic acids, etc. - were also continuously formed in the atmosphere under the influence of hard ultraviolet radiation from the Sun, high temperatures in areas of lightning discharges and active volcanic activity.
Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, conditions for the abiogenic occurrence of organic compounds were : the reducing nature of the Earth's atmosphere (compounds with reducing properties easily interact with each other and oxidizing substances), high temperature, lightning discharges and powerful ultraviolet radiation from the Sun, which were not yet blocked by the ozone screen.
The primary ocean apparently contained in dissolved form various organic and inorganic molecules that entered it from the atmosphere and were washed out from the surface layers of the Earth. The concentration of organic compounds constantly increased, and eventually the waters of the ocean became ʼʼ brothʼʼ made of protein-like substances– peptides, as well as nucleic acids and other organic compounds.
Organic molecules have a large molecular weight and a complex spatial configuration. Οʜᴎ are surrounded by a water shell and combine to form high molecular weight complexes - coacervates, or coacervate drops (as A.I. Oparin called them). Coacervates had the ability to absorb various substances dissolved in the waters of the primary ocean. As a result of this, the internal structure of the coacervate changed, which led either to its disintegration or to the accumulation of substances, i.e., to growth and changes in the chemical composition, increasing the stability of the coacervate droplet in constantly changing conditions.
In the mass of coacervate drops happened selection most sustainable under these specific conditions. Having reached a certain size, the mother coacervate droplet could disintegrate into daughter drops, but only those daughter drops continued to exist. coacervate drops who, entering to elementary forms of exchange with the environment , maintained relative constancy of their composition. Further they acquired the ability to absorb not all from the environment substances , but only those that ensured their stability, and also excrete metabolic products . In parallel, the differences between the chemical composition of the drop and the environment increased. During the long selection process(chemical evolution) only those coacervates are preserved, which upon decay into daughter did not lose the structural features, i.e. acquired self-reproduction properties .
During evolution, the most important components of coacervate droplets - polypeptides – developed the ability to catalytic activity, i.e. to a significant acceleration of biochemical reactions, leading to the transformation of organic compounds, and polynucleotides turned out to be able to communicate with each other according to the principle of complementation and, therefore, carry out non-enzymatic synthesis subsidiaries polynucleotide chains.
The next important step prebiological evolution – unification of the ability of polynucleotides to reproduce themselves with the ability of polypeptides to accelerate the course of chemical reactions, since the doubling of DNA molecules is more efficiently carried out with the participation of proteins with catalytic activity. Nucleic acid communication And protein molecules eventually led to emergence of genetic code, i.e., such an organization of DNA molecules in which the sequence of nucleotides began to serve as information for constructing a specific sequence of amino acids in proteins.
Further progressive evolution prebiological structures led to the formation of lipid layers (lipid boundaries), between coacervates, rich in organic compounds, and surrounding aquatic environment. In the process of subsequent evolution lipids transformed into the outer membrane , significantly increasing the viability and stability of organisms. The appearance of the membrane predetermined the direction of further chemical evolution along the path of development of ever more advanced self-regulating systems until the emergence first cells .
Thus, occurrence in physicochemical system ( coacervate) metabolism (metabolism) and accurate self-reproduction - this is the main prerequisite for the emergence of a biological system - a primitive heterotrophic anaerobic cell.
Biogeochemical functions of life due to their diversity and complexity, they could not be associated only with any one form of life. Primary biosphere was originally presented rich functional diversity. Primary biocenoses consisted of the simplest unicellular organisms, since without exception, all the functions of living matter in the biosphere are performed by them.
Primary organisms, which arose on Earth about 3.8 billion years ago, had the following properties:
‣‣‣ were heterotrophic organisms , i.e. they fed on ready-made organic compounds accumulated at the stage of the cosmic evolution of the Earth;
‣‣‣ were prokaryotes – organisms lacking a formed nucleus;
‣‣‣ were anaerobic organisms using yeast fermentation as an energy source;
‣‣‣ appeared in the form primary biosphere , consisting of biocenoses, including various types of single-celled organisms;
‣‣‣ appeared and existed for a long time only in the waters primary ocean .
The emergence of a primitive cell signified the end of the prebiological evolution of living things and the beginning of the biological evolution of life . It is believed that the selection of coacervates and the boundary stage of chemical and biological evolution lasted about 750 million years. At the end of this period (at about 3.8 billion years ago), first primitive anucleate cells – prokaryotes (mostly bacterial level) . The first living organisms - heterotrophs – used organic compounds dissolved in the waters of the primary ocean as a source of energy (food). Since there was no free oxygen in the Earth's atmosphere, heterotrophs had an anaerobic (oxygen-free) type of metabolism, the efficiency of which is low. The increase in the number of heterotrophs led to the depletion of the waters of the primary ocean, where there was less and less ready-made organic matter that could be used for nutrition.
Organisms that have developed the ability to use the energy of solar radiation are in a more advantageous position. For synthesis of organic matter from inorganic – photosynthesis . Transition of the living to photosynthesis and autotrophic type of nutrition was a turning point in the evolution of living things. The Earth's atmosphere began to be “filled” with oxygen, which was poison for anaerobes. For this reason, many unicellular anaerobes died, but some adapted to oxygen. The first photosynthetic organisms, releasing oxygen into the atmosphere, were cyanobacteria (cyanea). Transition to photosynthesis was a long process and ended around1,8 billion years ago. With the advent of photosynthesis, more and more energy from sunlight accumulated in the organic matter of the Earth, which accelerated the biological cycle of substances and the evolution of living things in general.
In an oxygen environment they formed eukaryotes , i.e. unicellular, having a core organisms. These were already more advanced organisms with photosynthetic ability. Their DNA were already concentrated V chromosomes , whereas in prokaryotic cells the hereditary substance was distributed throughout the cell. Eukaryotic chromosomes were concentrated in cell nucleus , and the cell itself was already reproducing without significant changes. Many modern scientists have accepted hypothesis about the emergence eukaryotic cells through a series of successive symbioses, because it is well founded. First of all, unicellular algae even now easily enter into an alliance with animals - eukaryotes (for example, chlorella algae lives in the body of the ciliate slipper). Secondly, some cell organelles - mitochondria and plastids - are very similar in DNA structure to prokaryotic bacterial cells and cyanobacteria.
Subsequent evolution eukaryotes was associated with the division into vegetable And animals cells. This division occurred in the Proterozoic, when the Earth was inhabited by single-celled organisms.
Plant cells have evolved to reduce the ability to move due to the development of a tough cellulose membrane, but to use photosynthesis.
Animal cells have evolved to increase their ability to move and improve their ability to absorb and excrete food products.
The next stage in the development of living things was sexual reproduction. It arose approximately 900 million years ago.
A further step in the evolution of living things occurred about 700-800 million years ago, when multicellular organisms with a differentiated body, tissues and organs that perform specific functions. These were sponges, coelenterates, arthropods, etc., related to multicellular animals.
Throughout the Proterozoic and at the beginning of the Paleozoic, plants inhabited mainly seas and oceans. It was mainly green and red algae.
Cambrian period was marked by the massive appearance animals with mineral skeletons (lime, phosphate, flint). Among the marine animals of that time, crustaceans, sponges, corals, mollusks, trilobites, etc. are known. Terrestrial biota in the Cambrian was represented by bryophytes, lichens and the first multicellular animals, such as worms and arthropods (centipedes). Cyanobionts developed abundantly in the seas.
IN late Ordovician Large carnivores, as well as fish-like jawless vertebrates, began to appear.
Most notable event Silurian is associated with land. For the first time, true higher plants (cooksonia, etc.) appeared that had a herbaceous appearance. Οʜᴎ were closely associated with moisture-intensive areas of the coasts. Among animal organisms - arthropods - reliable terrestrial representatives also appeared - chelicerates.
IN Devonian the first is typical for terrestrial spaces massive development higher plants (rhiniophytes, psilophytes, lycophytes and ferns). Further evolution vertebrates walked in the direction of the jawed fish-like creatures. In the Devonian, vertebrates are represented by three groups real fish: lungfish, ray-finned and lobe-finned fish. Only lobe-finned fish were able to adapt to life on land thanks to their muscular limbs and lungs. At the end of the Devonian, lobe-finned fish gave rise to the first terrestrial amphibians (vertebrates). At the end of the Devonian, insects appeared (the food supply for future terrestrial vertebrates).
The transition to life in the air required many changes from living organisms and presupposed the development of appropriate adaptations. He sharply increased the rate of evolution of life on Earth.
So, carbon , or Carboniferous period, was time of intensive formation and diversification for higher plants, terrestrial invertebrates and vertebrates. For higher plants carbon - ϶ᴛᴏ time heyday lycophytes, arthropods (or horsetails), ferns and the first gymnosperms, the woody forms of which reached a height of 20-40 m (for example, Lepidodendron). The flourishing of vegetation and the emergence of various ecological niches is closely related to the development of terrestrial conditions by mollusks, arachnids and insects. In the Carboniferous, invertebrates first mastered airspace. Particularly striking at that time were giant dragonfly-like creatures with a wingspan of up to 2 m and cockroaches up to 3 cm long. And the morphophysiological and ecological diversity of amphibians led to the appearance of reptiles. They were the first vertebrate reptiles to adapt to living conditions on land. Their eggs were covered with a hard shell, were not afraid of drying out, and were supplied with food and oxygen for the embryo.
Permian period The development of the organic world is characterized primarily by the catastrophic extinction of marine biota (from 400 families at the beginning to 200 at the end). This was associated with global climate aridization, intense mountain building and associated glaciation.
Feature Triassic period is the transitional nature of the systematic composition of the biota. For example, new groups of aquatic reptiles appeared - fish-like ichthyosaurs, plesiosaurs with a long serpentine neck, a small head, a body with flippers and a shortened tail. The diversity of terrestrial reptiles has increased. Dinosaurs and pterosaurs arose. Numerous animal-like reptiles continued to exist, giving rise to Late Triassic first mammals small in size (oviparous), externally resembling rats. IN Late Triassic arose and birds . With the advent of birds and mammals, animals gained warm-blooded, although some reptiles probably also possessed it.
As part of terrestrial vegetation Glottals predominated (Bennettiaceae, Cycadaceae, Conifers, etc.), and ferns are represented by new groups that reached their peak in the Jurassic.
IN Jurassic Biodiversity in the marine and terrestrial environment is rapidly increasing. Observed in the Jurassic bloom of reptiles . Οʜᴎ were represented by all environmental groups. Aquatic representatives (ichthyosaurs, plesiosaurs) continued to exist. Saurian and ornithischian dinosaurs lived on land. In the Jurassic, the composition of flying lizards was updated. Birds were represented by lizard-tailed birds - Archeopteryx. A new subclass of mammals has emerged – marsupials . Among invertebrates it was observed heyday ground insects .
Ground vegetation characterized blossoming of ferns (tree forms and vines) and voices (cycads and bennettites), which formed the forests of the tropics and subtropics.
Major biotic event Cretaceous period – appearance And intensive development angiosperms (flowering) plants.
In the Cretaceous period, the specialization of reptiles (reptiles) continued, they reached enormous sizes; Thus, the mass of some dinosaurs exceeds 50 tons. The parallel evolution of flowering plants and pollinating insects begins. Appeared in the chalk first placental mammals(insectivores, ancient ungulates, early primates, and also, possibly, cat-like carnivores).
At the end of the Cretaceous period (67 million years ago), there was a mass extinction of many groups of animals and plants. This global environmental crisis was on a smaller scale than the Permian-Triassic crisis. At the same time, as a result of this cooling, the area of semi-aquatic vegetation decreased; herbivores became extinct, followed by predatory dinosaurs (large reptiles survived only in the tropical zone); many forms of invertebrates and sea lizards became extinct in the seas; Warm-blooded animals - birds and mammals - received an advantage in natural selection.
Cenozoic era- ϶ᴛᴏ time domination flowering plants, insects, birds And mammals. Viviparity of mammals and feeding of their young with milk was a powerful factor in their evolution, allowing them to reproduce in a variety of environmental conditions. The developed nervous system contributed to a variety of forms of adaptation and protection of organisms.
Paleogene(especially Eocene) – a time of widespread global distribution of the following mammals: oviparous, marsupials, but the determining factor was the diversity of placentals (ancient predators, ancient ungulates, primitive primates, etc.). Scaly reptiles and turtles also lived on land, and crocodiles lived in fresh water bodies. The new toothless birds are quite diverse. Among aquatic vertebrates, bony fish predominated. Marine invertebrates are diverse.
In the Neogene, amphibians and reptiles gradually acquired their modern appearance. Large ostrich-like birds attract attention. The flourishing of placental mammals continued: odd-toed (hipparions) and even-toed (deer, camels, pigs), new predators (saber-toothed tigers), proboscis (mastodons). By the end of the Neogene, all modern families of mammals were already found.
The decisive stage in the evolution of life on Earth was development of the order of primates. In the Cenozoic, approximately 67-27 million years ago, primates divided into lower and great apes, which are the most ancient ancestors of modern humans.
Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, in the fossil record to impressive mass appearances Life can include many events. Of these, we will indicate the following, noting the beginning of their appearance (see MGS):
● 3.8–3.5 billion years (AR1 – Eoarchean). The emergence of life. The appearance of bacteria and cyanobionts. The lithosphere begins to be enriched with rocks of biogenic origin (graphites, shungites).
● 3.2 billion years (AR2/AR3 – paleoarchean/mesoarchean). Mass development of cyanobionts. The lithosphere acquires biogenic carbonate strata called stromatolitic. The atmosphere begins to be enriched with molecular oxygen released by cyanobionts during photosynthesis.
● 1.6 billion years (PR1/PR2 – Paleoproterozoic/Mesoproterozoic). The appearance of aerobic bacteria, lower algae, animals and fungi.
● 1.0–0.7 Ga (PR3 – Neoproterozoic). The appearance of reliable multicellular algae and non-skeletal invertebrates, represented by cnidarians, worms, arthropods, (?) echinoderms and other groups.
● 542.0 ±1.0–521 (530) Ma (Early Cambrian). Mass appearance of mineral skeletons in the Animal Kingdom in almost all known types.
● 416.0±2.8 Ma (S2/D1 – Late Silurian/Early Devonian). Mass appearance of terrestrial vegetation.
● 359.2±2.5 million years (D/C – Late Devonian/Early Carboniferous). Mass appearance of the first terrestrial invertebrates (insects, arachnids) and vertebrates (amphibians, reptiles).
● 65.5±0.3 million years (MZ/KZ – the boundary of the Mesozoic and Cenozoic). Mass appearance of angiosperms and mammals.
● 2.8 million years (N2 – Pliocene, Piacenza). The appearance of man.
Today described more 1 million animal species, near 0.5 million plant species, hundreds of thousands of species of fungi, more than 3 thousand species of bacteria. It is estimated that at least 1 million species remain undescribed. Modern biology highlights five kingdoms : Bacteria, Cyanobionts, Plants, Fungi, Animals.
The problem of the beginning and evolution of life on Earth. - concept and types. Classification and features of the category "The problem of the beginning and evolution of life on Earth." 2017, 2018.
The appearance of a primitive cell meant the end of the prebiological evolution of living things and the beginning of the biological evolution of life.
The first single-celled organisms to appear on our planet were primitive bacteria that did not have a nucleus, that is, prokaryotes. As already indicated, these were single-celled, nuclear-free organisms. They were anaerobes, because they lived in an oxygen-free environment, and heterotrophs, because they fed on ready-made organic compounds of the “organic broth,” that is, substances synthesized during chemical evolution. Energy metabolism in most prokaryotes occurred according to the fermentation type. But gradually the “organic broth” decreased as a result of active consumption. As it was exhausted, some organisms began to develop ways to form macromolecules biochemically, inside the cells themselves with the help of enzymes. Under such conditions, cells that were able to receive most of the required energy directly from solar radiation turned out to be competitive. The process of formation of chlorophyll and photosynthesis followed this path.
The transition of living things to photosynthesis and the autotrophic type of nutrition was a turning point in the evolution of living things. The Earth's atmosphere began to be “filled” with oxygen, which was poison for anaerobes. Therefore, many unicellular anaerobes died, others took refuge in oxygen-free environments - swamps and, while feeding, released methane rather than oxygen. Still others have adapted to oxygen. Their central metabolic mechanism was oxygen respiration, which made it possible to increase the yield of useful energy by 10–15 times compared to the anaerobic type of metabolism - fermentation. The transition to photosynthesis was a long process and was completed about 1.8 billion years ago. With the advent of photosynthesis, more and more energy from sunlight accumulated in the organic matter of the Earth, which accelerated the biological cycle of substances and the evolution of living things in general.
In an oxygen environment, eukaryotes, that is, single-celled organisms with a nucleus, formed. These were already more advanced organisms with photosynthetic ability. Their DNA was already concentrated into chromosomes, whereas in prokaryotic cells the hereditary substance was distributed throughout the cell. Eukaryotic chromosomes were concentrated in the cell nucleus, and the cell itself was already reproducing without significant changes. Thus, the daughter cell of eukaryotes was almost an exact copy of the mother cell and had the same chance of survival as the mother cell.
Education of plants and animals
The subsequent evolution of eukaryotes was associated with the division into plant and animal cells. This division occurred in the Proterozoic, when the Earth was inhabited by single-celled organisms.
From the beginning of evolution, eukaryotes developed dually, that is, they simultaneously had groups with autotrophic and heterotrophic nutrition, which ensured the integrity and significant autonomy of the living world.
Plant cells have evolved to reduce the ability to move due to the development of a tough cellulose membrane, but to use photosynthesis.
Animal cells have evolved to increase their ability to move and improve their ability to absorb and excrete food products.
The next stage in the development of living things was sexual reproduction. It arose approximately 900 million years ago.
A further step in the evolution of living things occurred about 700–800 million years ago, when multicellular organisms appeared with differentiated bodies, tissues and organs that perform specific functions. These were sponges, coelenterates, arthropods, etc., related to multicellular animals.
Throughout the Proterozoic and at the beginning of the Paleozoic, plants inhabited mainly seas and oceans. These are green and brown, golden and red algae. Subsequently, many types of animals already existed in the Cambrian seas. Later they specialized and improved. Among the marine animals of that time were crustaceans, sponges, corals, mollusks, and trilobites.
At the end of the Ordovician period, large carnivores, as well as vertebrates, began to appear.
Further evolution of vertebrates went in the direction of jawed fish-like animals. In the Devonian, lungfish - amphibians, and then insects - began to appear. The nervous system gradually developed as a consequence of the improvement of forms of reflection.
A particularly important stage in the evolution of living forms was the emergence of plant and animal organisms from water to land and a further increase in the number of species of terrestrial plants and animals. In the future, it is from them that highly organized forms of life arise. The emergence of plants on land began at the end of the Silurian, and the active conquest of land by vertebrates began in the Carboniferous.
The transition to life in the air required many changes from living organisms and presupposed the development of appropriate adaptations. He sharply increased the rate of evolution of life on Earth. Man became the pinnacle of the evolution of living things. Life in the air has “increased” the body weight of organisms, the air does not contain nutrients, air transmits light, sound, heat differently than water, and the amount of oxygen in it is higher. It was necessary to adapt to all this. The first vertebrates to adapt to living conditions on land were reptiles. Their eggs were supplied with food and oxygen for the embryo, covered with a hard shell, and were not afraid of drying out.
About 67 million years ago, birds and mammals gained an advantage in natural selection. Thanks to the warm-blooded nature of mammals, they quickly gained a dominant position on Earth, which is associated with cooling conditions on our planet. At this time, it was warm-bloodedness that became the decisive factor for survival.
It ensured a constant high body temperature and stable functioning of the internal organs of mammals. Viviparity of mammals and feeding of their young with milk was a powerful factor in their evolution, allowing them to reproduce in a variety of environmental conditions. The developed nervous system contributed to a variety of forms of adaptation and protection of organisms. There was a division of carnivorous animals into ungulates and predators, and the first insectivorous mammals marked the beginning of the evolution of placental and marsupial organisms.
The decisive stage in the evolution of life on our planet was the emergence of the order of primates. In the Cenozoic, approximately 67–27 million years ago, primates divided into lower and great apes, which are the most ancient ancestors of modern humans. The prerequisites for the emergence of modern man in the process of evolution were formed gradually.
At first there was a herd lifestyle. It made it possible to form the foundation of future social communication. Moreover, if in insects (bees, ants, termites) biosociality led to the loss of individuality, then in the ancient ancestors of humans, on the contrary, it developed the individual traits of the individual. This was a powerful driving force for the development of the team.
Eras and periods
According to modern estimates, the age of the Earth is about 4.5-5 billion years. The appearance on the planet of the first bodies of water, with which the origin of life is associated, is 3.8-4 billion years distant from the present. The history of the Earth is usually divided into large periods of time - eras and periods. The boundaries between them are major geological events associated with the history of the development of the planet as a cosmic body. Such events include mountain-building processes, increased volcanic activity, rise and fall of land, changes in the outlines of continents and oceans.
The geochronological history of the Earth consists of 5 eras.
^ Table 1. Chronology of major events in the evolution of multicellular organisms
| Era | Period | Beginning, million years ago | Brief geological setting | Major evolutionary events |
| Cenozoic | Quaternary | 2,4 | Design of modern outlines of continents and relief. Repeated climate changes. Four major glaciations of the Northern Hemisphere | The extinction of many plant species, the decline of woody forms, the flourishing of herbaceous forms. Human evolution. Extinction of large mammal species. |
| Neogene | Widespread mountain rise. The climate is close to modern in its characteristics. | The predominance of angiosperms and conifers, an increase in the area of steppes. The rise of placental mammals. The emergence of great apes. | ||
| Paleogene | The climate is warm | The heyday of angiosperms, mammals, birds. | ||
| Mesozoic | Chalk | Cooling climate in many areas. | Development of mammals, birds, flowering plants. Extinction of many reptiles. | |
| Yura | The climate is humid, warm, and dry towards the end of the period. | Dominance of reptiles on land, water and air. The emergence of angiosperms and birds. | ||
| Triassic | The appearance of mammals. The flourishing of reptiles, the spread of gymnosperms. | |||
| Paleozoic | Permian | The retreat of the seas, the increase in volcanic activity, the climate became sharply continental, drier and colder. | The Great Marine Dying. The appearance of gymnosperms, the spread of reptiles. | |
| Carbon | Lowering the level of continents. The climate is initially warm and humid, then cool. | The appearance of reptiles. | ||
| Devonian | The appearance of ancient amphibians and insects. Dominance of fish. The appearance of forests of ferns and mosses. | |||
| Silur | Formation of a single Euro-American continent. The rise of continents, the establishment of lowlands. The climate is warm, humid and alternates with dry. | Exit of plants and invertebrates to land. | ||
| Ordovician | The climate is warm and humid. | Abundance of seaweed. Appearance of the first vertebrates (jawless). | ||
| Cambrian | Subsidence of continents and widespread flooding of them by seas. The climate is temperate, dry, alternately humid. | Life is concentrated in the seas. Development of invertebrates. The appearance of higher plants. | ||
| Proterozoic | Late Proterozoic | 1650 | Development of eukaryotes, multicellular plants and animals | |
| Early Proterozoic | 2600 | Development of lower plants | ||
| Archaeozoic | 4000 | The origin of life, the emergence of prokaryotes. The dominance of bacteria and blue-greens, the appearance of green algae. |
For ease of study, the history of the development of the Earth is divided into four eras and eleven periods. The two most recent periods are in turn divided into seven systems or eras.
The earth's crust is stratified, i.e. the various rocks that make it up lie in layers on top of each other. As a rule, the age of rocks decreases towards the upper layers. The exception is areas with disturbed layers due to movements of the earth's crust. William Smith in the 18th century noticed that over geological periods of time some organisms made significant advances in their structure.
According to modern estimates, the age of planet Earth is approximately 4.6 - 4.9 10 years. These estimates are based mainly on the study of rocks using radiometric dating methods.
ARCHAY
Not much is known about life in the Archean. The only animal organisms were cellular prokaryotes - bacteria and blue-green algae. The products of the vital activity of these primitive microorganisms are also the oldest sedimentary rocks (stromatolites) - pillar-shaped calcareous formations found in Canada, Australia, Africa, the Urals, and Siberia.
Sedimentary rocks of iron, nickel, and manganese have a bacterial basis. Many microorganisms are active participants in the formation of colossal, as yet poorly diluted mineral resources on the bottom of the World Ocean. The role of microorganisms in the formation of oil shale, oil and gas is also great. Blue-green bacteria quickly spread through the archaea and become masters of the planet. These organisms did not have a separate nucleus, but a developed metabolic system and the ability to reproduce. Blue-greens, in addition, possessed a photosynthetic apparatus. The appearance of the latter was the largest aromorphosis in the evolution of living nature and opened one of the ways (probably specifically terrestrial) for the formation of free oxygen. Towards the end of the Archean (2.8-3 billion years ago), the first colonial algae appeared, the fossilized remains of which were found in Australia, Africa, etc. The most important stage in the development of life on Earth is closely related to changes in the concentration of oxygen in the atmosphere and the formation of the ozone screen. Thanks to the vital activity of blue-greens, the content of free oxygen in the atmosphere has increased significantly. The accumulation of oxygen led to the emergence of a primary ozone screen in the upper layers of the biosphere, which opened the horizons for prosperity.
PROTEROZOIC
Proterozoic is a huge stage in the historical development of the Earth. During this period, bacteria and algae reach exceptional prosperity, and with their participation the processes of sedimentation proceed intensively. As a result of the vital activity of iron bacteria in the Proterozoic, the largest iron ore deposits were formed. At the turn of the Early and Middle Riphean, the dominance of prokaryotes was replaced by the flourishing of eukaryotes - green and golden algae. From unicellular eukaryotes, multicellular organisms with complex organization and specialization develop in a short time. The oldest representatives of multicellular animals are known from the late Riphean (700-600 million years ago). Now we can say that 650 million years ago, the earth’s seas were inhabited by a variety of multicellular organisms: solitary and colonial polyps, jellyfish, flatworms, and even the ancestors of modern annelids, arthropods, mollusks and echinoderms. Among plant organisms at that time, unicellular organisms predominated, but multicellular algae (green, brown, red) and fungi also appeared.
PALEOZOIC
By the beginning of the Paleozoic era, life had passed perhaps the most important and difficult part of its journey. Four kingdoms of living nature were formed: prokaryotes, or shotguns, mushrooms, green plants, animals. The ancestors of the kingdom of green plants were unicellular green algae, common in the seas of the Proterozoic. Along with floating forms, those attached to the bottom also appeared among the bottom. A fixed lifestyle required dismemberment of the body into parts. But the acquisition of multicellularity, the division of a multicellular body into parts that perform different functions, turned out to be more promising. The emergence of such an important aromorphosis as the sexual process was of decisive importance for further evolution.
How and when did the division of the living world into plants and animals occur? Is their root the same? Disputes among scientists around this issue do not subside even today. Perhaps the first animals descended from the common stem of all eukaryotes or from single-celled green waters growing up.
CAMBRIAN
The rise of skeletal invertebrates. During this period, another period of mountain building and redistribution of land and sea areas took place. The Cambrian climate was temperate, the continents unchanged. Only bacteria and blue-greens still lived on land. The seas were dominated by green and brown algae attached to the bottom; Diatoms, golden algae, and euglena algae swam in the water columns. As a result of the increased washout of salts from land, marine animals were able to absorb large quantities of mineral salts. And this, in turn, opened up wide ways for them to build a rigid skeleton. The most widespread arthropods - trilobites, which are similar in appearance to modern crustaceans - wood lice, have reached the widest distribution. Very characteristic of the Cambrian is a peculiar type of multicellular animals - archaeocyaths, which became extinct towards the end of the period. At that time, there were also a variety of sponges, corals, brachiopods, and mollusks. Sea urchins appeared later .
ORDOVIK
In the Ordovician seas, green, brown and red algae and numerous trilobites were diversely represented. In the Ordovician, the first cephalopods, relatives of modern octopuses and squids, appeared, and brachiopods and gastropods spread. There was an intensive process of reef formation by four-rayed corals and tabulates. Graptolites are widespread - hemichordates, combining the characteristics of invertebrates and vertebrates, reminiscent of modern lancelets. In the Ordovician, spore-bearing plants appeared - psilophytes, growing along the banks of fresh water bodies.
SILUR
The warm shallow seas of the Ordovician were replaced by large areas of land, which led to a dry climate.
In the Silurian seas, graptolites lived out their lives, trilobites fell into decline, but cephalopods reached exceptional prosperity. Corals gradually replaced archaeocyaths. In the Silurian, peculiar arthropods developed - giant crustacean scorpions, reaching up to 2 m in length. By the end of the Paleozoic, the entire group of crustacean scorpions almost became extinct. They resembled the modern horseshoe crab. A particularly noteworthy event of this period was the appearance and spread of the first representatives of vertebrates - armored “fish”. These “fish” only resembled real fish in shape, but belonged to a different class of vertebrates - jawless or cyclostomes. They could not swim for long and mostly lay at the bottom of bays and lagoons. Due to their sedentary lifestyle, they were unable to develop further. Among the modern representatives of cyclostomes, lampreys and hagfishes are known. A characteristic feature of the Silurian period is the intensive development of land plants. One of the first terrestrial, or rather amphibian, plants were psilophytes, which trace their ancestry to green algae. In reservoirs, algae adsorb water and substances dissolved in it over the entire surface of the body, which is why they do not have roots, and body outgrowths resembling roots serve only as attachment organs. Due to the need to conduct water from the roots to the leaves, a vascular system arises. The emergence of plants onto land is one of the greatest moments of Evolution. It was prepared by the previous evolution of the organic and inorganic world.
DEVONIAN
Devon is the period of fishes. The Devonian climate was more sharply continental; icing occurred in the mountainous regions of South Africa. In warmer areas, the climate changed towards greater drying, and desert and semi-desert areas appeared.
In the Devonian seas, fish flourished. Among them were cartilaginous fish, and fish with a bony skeleton appeared. Based on the structure of their fins, bony fish are divided into ray-finned and lobe-finned. Until recently, it was believed that lobe-finned animals became extinct at the end of the Paleozoic. But in 1938, a fishing trawler delivered such a fish to the East London Museum and it was named coelacanth. At the end of the Paleozoic, the most significant stage in the development of life was the conquest of land by plants and animals. This was facilitated by the reduction of sea basins and the rise of land.
Typical spore plants evolved from psilophytes: mosses, horsetails, and pteridophytes. The first forests appeared on the earth's surface.
By the beginning of the Carboniferous, noticeable warming and humidification occurred. In the vast valleys and tropical forests, in continuous summer conditions, everything grew rapidly upward. Evolution has opened a new way - propagation by seeds. Therefore, gymnosperms picked up the evolutionary baton, and spore plants remained a side branch of evolution and faded into the background. The emergence of vertebrates onto land occurred back in the Late Devonian period, after the land conquerors - the psilophytes. At this time, the air had already been mastered by insects, and the descendants of lobe-finned fish began to spread across the earth. The new method of movement allowed them to move away from the water for some time. This led to the emergence of creatures with a new way of life - amphibians. Their most ancient representatives - ichthyoshegs - were discovered in Greenland in Devonian sedimentary rocks. The heyday of ancient amphibians dates back to the Carboniferous. It was during this period that stegocephals developed widely. They lived only in the coastal part of the land and could not conquer inland areas located far from bodies of water.
Thanks to these structural features, amphibians took the first decisive step onto land, but their descendants, the reptiles, became the complete masters of the land. The development of an arid climate in the Permian period led to the extinction of stegocephalians and the development of reptiles, in the life cycle of which there are no stages associated with water. Due to the land way of life, several major aromorphoses arose in reptiles.
MESOZOIC
The Mesozoic is rightly called the era of reptiles and gymnosperms. Towards the end of the Mesozoic, a mass extinction of dinosaurs gradually occurred over several million years. The dominance of dinosaurs throughout the entire geological era and their near extinction at the end of the era constitute a great mystery to paleontologists. In the Triassic, the first representatives of warm-blooded animals arose - small primitive mammals. In the Jurassic, reptiles are the second group of animals that makes an attempt to master the air environment. There were two types of flying lizards: rhamphorhynchus and broad-winged lizards. From the amazing diversity of the former class of reptiles, 6,000 species have survived today. These are representatives of five evolutionary branches: tuataria, lizards, snakes, turtles, crocodiles. Birds appeared in the Jurassic period. They represent a lateral branch of reptiles that have adapted to flight. The Jurassic first bird, Archeopteryx, had a particularly strong resemblance to reptiles. The Cretaceous period is so named due to the abundance of chalk in the marine sediments of that time. It was formed from the remains of the shells of protozoan animals - foraminifera. At the beginning of the Cretaceous period, the next major shift in the evolution of plants occurred - flowering plants (angiosperms) appeared. These aromorphic changes provided flowering plants with biological progress in the next Cenozoic era. They have widely populated the Earth and are characterized by great diversity. Some of their forms have survived to this day: poplars, willows, oaks, eucalyptus, palm trees.
Cenozoic
Cenozoic - the era of new life - the heyday of flowering plants, insects, birds, and mammals.
During the time of the dinosaurs, a group of mammals was known - small in size, furry animals that arose from theraspids or beast-like animals. Viviparity, warm-bloodedness, a more developed brain and the greater activity associated with it thus ensured the progress of mammals, their rise to the forefront of evolution. In the Tertiary period, mammals took a dominant position, adapting to various conditions on land, in the air, in water, and, as it were, replaced the Mesozoic reptiles. In the Paleocene and Eocene, the first predators evolved from insectivores, and modern groups of carnivores branched off from them in the Oligocene. They began to conquer the seas. And also the first ungulates originated from the ancient Paleocene carnivores.
Due to the aridity of some areas, cereal plants appeared.
Already in the first half of the Tertiary period, all modern orders of mammals had emerged, and by the middle of the period, the common ancestral forms of apes and humans were widespread. During the Quaternary period, mastodons, mammoths, saber-toothed tigers, giant sloths, and big-horned peat deer became extinct.
Man settled in the Old World at least 500 thousand years ago. Before the glaciation, hunters settled as far as Tierra del Fuego. As the glaciers melted, the territories freed from under the glaciers were re-populated by humans.
About 10,000 years ago, the domestication of animals and the introduction of plants into culture began in warm temperate regions of the Earth. The “Neolithic revolution” began, associated with the transition of man from gathering and hunting to agriculture and cattle breeding.
Lecture 6: Formation of biological diversity during different periods of biosphere development
Purpose of the lecture: a description of the main changes that occurred with the continents of the Earth, with its flora and fauna during the history of our planet from its appearance to modern times.
Issues covered:
1.Archean era and Proterozoic
2.Introduction to the Paleozoic using the example of the Carboniferous period
3. The scale and essence of the differences between the Carboniferous and Carboniferous periods.
4. The scale and essence of the differences between carbon fiber and the modern era.
5. A. Wagener’s theory of continental drift and the theory of plate tectonics.
6. The role of living organisms in creating conditions for life to reach land.
7. An idea of the Mesozoic using the example of the Cretaceous period.
8.Revolution in the composition of the flora due to the expansion of angiosperms.
9. Heat-loving marine fauna of cephalopods and dinosaur fauna.
10. The appearance of placental mammals and birds of a modern type of organization.
11. Cenozoic era and anthropogen. The appearance of man. The development of glaciations and their impact on humanity. Main trends in the evolution of the biosphere.
1. This lecture describes the main changes that occurred with the continents of the Earth, with its flora and fauna during the history of our planet from its appearance to modern times. The main development paths through which life passed are indicated, and its main representatives that lived in different natural conditions and in different geological eras are identified. The general diagram of the evolution of the animal world over more than one billion years is shown in Fig. 1. The entire animal world has developed from common ancestors - ancient primitive single-celled organisms (1). From them came both various unicellular (2, 3, 4) and multicellular animals. As the animal world developed, more and more highly organized animals appeared. Primitive bilayers (13) gave rise to the development of two different evolutionary branches. Moreover, one branch led to the development of higher invertebrates: mollusks, crustaceans, insects, and the other - to the development of vertebrates. Thus, these two groups of animals developed independently of each other. The numbers indicate various groups of animals, both existing and some extinct, which are indicated by circles with a black outline.
Rice. 1. Scheme of animal development. 1 - primary unicellular; 2 - amoebas; 3 - ciliates; 4 - flagella; 5 - first colonial flagellates; 6 - sponges; 7 - lower two-layer multicellular; 8,9, 10 - coelenterates: coral polyps, hydra, jellyfish; 11 - flatworms; 12 - roundworms; 13 - ancient ctenophores; 14 - ctenophores; 15 - primitive rings; 16,17,18 - mollusks: gastropods (snail, bivalve shell), cephalopods (squid); 19 - crustaceans; 20 - arachnids; 21 - centipedes; 22 - non-insects; 23 - ringed worms (earthworm); 24 - sea rings; 25 - sea lilies; 26 - echinoderms; 27 – starfish; 28 - lower chordates; 29 - lancelet (skullless); 30 - ancient fish; 31 - modern fish; 32 - lobe-finned fish; 33 - amphibians; 34 - ancient reptiles (dinosaurs); 35 - reptiles; 36 - birds; 37 - mammals.
^ Archean and Proterozoic eras (from the origin of the planet to 540 million years ago). These eras lasted from the formation of the Earth until the appearance of the first multicellular organisms approximately 540 million years ago. The oldest rocks known to us are only 3.9 billion years old, so very little is known about the youth of our planet. Moreover, even these rocks have undergone such great transformations over billions of years that they can tell us little about them. About 2-3 billion years ago, the cores of continents separated by water began to form. By the end of the Proterozoic, they united into the first supercontinent Pangea, which included Africa in the center, America, the European and Siberian (Russian) plates in the north, and Antarctica, Australia, India and Arabia in the south.
^ Archean era. The first remains and signs of activity of living organisms date back to 3.5 billion years ago (deposits in South Africa). Life could appear only when favorable conditions were created for this, first of all, favorable temperature. Living matter, among other substances, is built from proteins. Therefore, by the time life originated, the temperature on the earth's surface had to drop enough so that proteins would not be destroyed. Many researchers studying the problem of the origin of life on Earth believe that life originated in shallow sea water as a result of complex physical and chemical processes inherent in inorganic matter. Certain chemical compounds form under certain conditions, and the likelihood of the formation of complex organic compounds is especially high for carbon atoms due to their specific characteristics. That is why carbon became the building material from which, according to the laws of physics and chemistry, the most complex organic compounds relatively emerged. Molecules did not immediately reach the required degree of complexity, so we can talk about chemical evolution, the process of which was rather slow.
The first living organisms could feed exclusively on organic substances, i.e. they were heterotrophic. But having exhausted the reserves of organic matter in their immediate environment, in the course of evolution some organisms (plants) acquired the ability to absorb the energy of solar rays and, with its help, split water into its constituent elements. Using hydrogen, they were able to convert carbon dioxide into carbohydrates and use it to build other organic substances in their bodies (the process of photosynthesis). With the advent of autotrophic organisms, the accumulation of free oxygen in the atmosphere began and the total amount of organic matter on Earth began to increase sharply. Immediately after the formation of our planet, the atmosphere contained a lot of hydrogen and helium, but they gradually evaporated into space and were gradually replaced by methane, nitrogen and carbon dioxide, which were released by rocks. And only as a result of the appearance and activity of living organisms in the atmosphere, the accumulation of oxygen began, which became necessary for the further development of life.
Living organisms of that time could exist exclusively in an introductory environment, since the water column reduced the harmful effects of ultraviolet radiation from space, as well as a number of harmful substances, the toxic effect of which decreased when dissolved. In addition, significant temperature fluctuations in the water were smoothed out. At the end of the Archean era, living beings were divided into prokaryotes and eukaryotes. It is assumed that the graphite found in sediments of that time is of organic origin and its amount corresponds to the amount of living matter of that time. The first material evidence of the origin of life was stromalolites - layered structures formed by cyanobacteria.
2. Proterozoic era. At this time, the further development of living things continues: there is a clear division of the three kingdoms of eukaryotes into plants, fungi and animals. Unicellular algae are especially widespread; the first multicellular green algae and lower fungi appear (1.4 billion years ago). Animals are represented by protozoa, and later the first multicellular organisms are discovered - representatives of the sponge and coelenterate types. These primitive creatures did not yet have a calcareous skeleton, but prints of their bodies are occasionally found. The existence of larger living creatures (worms) is indicated by clear zigzag prints - traces of crawling, as well as the remains of “minks” found in the sediments of the seabed. In 1947, Australian scientist R.K. Spriggs discovered an extremely interesting fauna in the Ediacara Hills (South Australia). It turned out that most of the animal species of the Ediacaran fauna that existed 600 million years ago belong to previously unknown groups of non-skeletal organisms. Some of them belong to the ancestors of jellyfish, sponges, arthropods, others resemble worms - annelids. Most animals of that time led a benthic lifestyle (mollusks), which is explained by the concentration of plants and organic substances on the bottom that served them as food.
In Fig. Figure 2 shows some organisms of the Ediacaran fauna.
Rice. 2. Late Proterozoic: 1-algae, 2-sponges, 3,6-gut-banded (3-jellyfish, 6-eight-rayed corals), 4,8-ringed worms, 5-echinoderms, 7-arthropods, 9-stromatolites (formed by cyanobacteria ).
3. Paleozoic era: Cambrian period (from 540 to 488 million years ago)
This period began with an astonishing evolutionary explosion, during which representatives of most of the main groups of animals known to modern science first appeared on Earth. The boundary between Precambrian and Cambrian is marked by rocks that suddenly reveal an astonishing variety of animal fossils with mineral skeletons - the result of the "Cambrian explosion" of life forms.
In the Cambrian period, large expanses of land were occupied by water, and the first supercontinent Pangea was divided into two continents - northern (Laurasia) and southern (Gondwana). There was significant erosion of the land, volcanic activity was very intense, the continents sank and rose, resulting in the formation of shoals and shallow seas, which sometimes dried out for several million years and then filled with water again. At this time, the oldest mountains appeared in Western Europe (Scandinavian) and central Asia (Sayans).
All animals and plants lived in the sea, however, the intertidal zone was already inhabited by microscopic algae, which formed terrestrial algal crusts. It is believed that the first lichens and terrestrial fungi began to appear at this time. The fauna of that time, first discovered in 1909 in the mountains of Canada by C. Walcott, was represented mainly by bottom organisms, such as archaeocyaths (analogues of corals), sponges, various echinoderms (starfish, sea urchins, sea cucumbers, etc. ), worms, arthropods (various trilobites, horseshoe crabs). The latter were the most common form of living creatures of that time (approximately 60% of all animal species were trilobites, which consisted of three parts - a head, a torso and a tail). All of them died out by the end of the Permian period; of the horseshoe crabs, only representatives of one family have survived to this day. Approximately 30% of Cambrian species were brachiopods - marine animals with bivalve shells, similar to mollusks. From trilobites that switched to predation, crustacean scorpions up to 2 m long appear. At the end of the Cambrian period, cephalopods appeared, including the genus of nautiluses, which is still preserved, and from echinoderms - primitive chordates (tunicates and anesculates). The appearance of the notochord, which gave rigidity to the body, was an important event in the history of the development of life.
^ Paleozoic era: Ordovician and Silurian periods (from 488 to 416 million years ago)
At the beginning of the Ordovician period, most of the southern hemisphere was still occupied by the great continent of Gondwana, while other large land masses were concentrated closer to the equator. Europe and North America (Laurentia) were pushed further apart by the expanding Iapetus Ocean. At first, this ocean reached a width of about 2000 km, then began to narrow again as the land masses that make up Europe, North America and Greenland began to gradually approach each other until they finally merged into a single whole. During the Silurian period, Siberia “swimmed” to Europe (the Kazakh small hills were formed), Africa collided with the southern part of North America, and as a result, a new giant supercontinent Laurasia was born.
After the Cambrian, evolution was characterized not by the emergence of completely new types of animals, but by the development of existing ones. In the Ordovician, the most severe flooding of land in the history of the earth occurred, as a result, most of it was covered with huge swamps; arthropods and cephalopods were common in the seas. The first jawless vertebrates appear (for example, the current cyclostomes - lampreys). These were bottom forms that fed on organic remains. Their body was covered with shields that protected them from crustacean scorpions, but there was no internal skeleton yet.
Approximately 440 million years ago, two significant events occurred at once: the emergence of plants and invertebrates onto land. In the Silurian there was a significant rise of land and a retreat of ocean waters. At this time, lichens and the first land plants resembling algae - psilophytes - appeared along the swampy shores of reservoirs, in the tidal zones. As an adaptation to life on land, an epidermis with stomata, a central conducting system, and mechanical tissue appear. Spores with a thick shell are formed, protecting them from drying out. Subsequently, the evolution of plants went in two directions: bryophytes and higher spore-bearing plants, as well as seed-bearing plants.
The emergence of invertebrates onto land was due to the search for new habitats and the absence of competitors and predators. The first terrestrial invertebrates were represented by tardigrades (which tolerate drying well), annelids, and then centipedes, scorpions and arachnids. These groups arose from trilobites that often found themselves on the shallows during low tides. In Fig. Figure 3 presents the main representatives of animals of the early Paleozoic.
Rice. 3. Early Paleozoic: 1-archaeocyaths, 2,3-coelenterates (2-four-rayed corals, 3-jellyfish), 4-trilobite, 5,6-mollusks (5-cephalopods, 6-gastropods), 7-brachiopods, 8, 9-echinoderms (9-crinoids), 10-graptolite (hemachordates), 11-jawless fishes.
Paleozoic era: Devonian period (from 416 to 360 million years ago)
The Devonian period was a time of greatest cataclysms on our planet. Europe, North America and Greenland collided with each other, forming the huge northern supercontinent Laurasia. At the same time, huge masses of sedimentary rocks were pushed up from the ocean floor, forming huge mountain systems in eastern North America (Appalachia) and western Europe. Erosion from rising mountain ranges has created large quantities of pebbles and sand. These formed extensive deposits of red sandstone. Rivers carried mountains of sediment into the sea. Wide swampy deltas were formed, which created ideal conditions for animals that dared to take the first, so important steps from water to land.
Among the invertebrate marine animals of this time, the second half of the Paleozoic era, the appearance of new marine predators of ammonites should be noted - cephalopods with a spirally twisted shell, often with a richly sculptured surface, as well as squids and octopuses. Vertebrates covered with a hard shell about 400 million years ago gave rise to primitive gnathostomes - armored cartilaginous fish (placoderms). The emergence of creatures with powerful bony jaws (like the 6 m long Dunkleosteus) is explained by the need to actively capture food and the transition to an actively swimming lifestyle. Later, from armored gnathostomes, cartilaginous fish (sharks, rays and chimaeras) appeared, the most common in the seas and fresh waters are ray-finned bony fish, the fins of which are long bony rays, now rare lungfish (that is, having both gills and lungs), as well as lobe-finned fish, which are currently represented by one relict genus - coelacanth. Lobe-finned and lungfish are the preserved forms of lobe-finned fish - their fleshy fins have bony processes at the base, from which bone rays extend.
At the end of the Devonian, vertebrates came to land. This is due to climate change and drying out of shallow water bodies. Lobe-finned fish, ancestral to terrestrial vertebrates, capable of breathing atmospheric air and crawling from body of water to body of water using fins, initially left water only for short periods. They moved poorly on land, using snake-like bends of their body for this purpose (as if they were swimming on land). Only gradually did paired limbs begin to play an increasingly important role in movement on land, which along the way turned from fins into limbs due to the need to hold on to the ground and push off from the bottom. The first amphibians that appeared 370 million years ago - acanthostegas, ichthyostegas and stegocephals (1-2 m long) - still had many fish-like characteristics in their structure. Thanks to intensive soil-forming processes and special climatic conditions, at the end of this period lowland forests appear, formed by a variety of tree-like horsetails, mosses, and ferns, which appeared in this period (380 million years ago). The spread of land invertebrates, mainly arthropods, began.
^ Paleozoic era: Carboniferous period (from 360 to 299 million years ago)
At the beginning of the Carboniferous period (Carboniferous), most of the earth's land was collected into two huge supercontinents: Laurasia in the north and Gondwana in the south. During the Late Carboniferous, both supercontinents steadily moved closer to each other. This movement pushed upward new mountain ranges that formed along the edges of the plates of the earth's crust, and the edges of the continents were literally flooded by streams of lava erupting from the bowels of the Earth. The climate cooled noticeably, and while Gondwana "swimmed" across the South Pole, the planet experienced at least two glaciations.
Thanks to the warm and humid climate of the Carboniferous period, tree-like spore plants flourished, the characteristic representatives of which were lycophytes (sigillaria and lepidodendrons 30-50 m high), giant horsetails (calamites), and various ferns. At this time, the first seed plants appeared that reproduce not by spores consisting of a single germ cell, but by multicellular seeds - seed ferns (pteridospermids) and gymnosperms (cordites). The emerging seed plants could settle in drier places, since the characteristics of their reproduction are not related to the availability of water. Huge forests of various trees, which after death formed thick layers of peat, became the basis for the formation of modern coal deposits.
Among the animals of this time, land animals became the most noticeable. In the Carboniferous period, the first primitive insects appeared, which are the most diverse of living organisms (more than a million species) - cockroaches, Coleoptera (beetles), Orthoptera (grasshoppers, crickets), Diptera (flies, mosquitoes), extinct dragonflies, which reached gigantic sizes ( up to 50 cm), other arthropods (spiders and scorpions) also develop. There is also a wide variety of amphibians with pronounced limbs, which had 5-8 fingers. Towards the end of the period the climate becomes increasingly arid and continental. This stimulated the emergence of a new group of animals - reptiles (reptiles) approximately 310 million years ago, which inhabited drier spaces, avoiding competition and predators. They developed a new evolutionary characteristic - internal fertilization and development of the embryo in the egg. Around the same time, four subclasses of reptiles appeared, differing in the structure of the skull: completely extinct anapsids (ancestors of turtles), animal-like lizards (synapsids), which became the ancestors of mammals, very diverse diapsids (lizards, snakes, crocodiles, dinosaurs and their descendants - birds), marine reptiles (ichthyosaurs) - parapsids.
^ Paleozoic Era: Permian Period (299 to 251 million years ago)
Throughout the Permian period, the supercontinent Gondwana and Laurasia gradually approached each other. Asia collided with Europe, throwing up the Ural mountain range. And in North America the Appalachians grew up. By the end of the Permian period, the formation of the giant supercontinent Pangea was completely completed. The Permian saw the largest retreat of the sea in Earth's history, and volcanic activity increased again. Large expanses of land were formed, and in the interior regions of the continents the climate became sharply continental. Significant glaciation occurred in almost all of modern Africa, Australia, and Antarctica.
At this time, a cold and dry climate reigned. The vast swampy coal forests disappeared, as almost all the giant mosses, horsetails and ferns, as well as the cordaites, became extinct. In their place, various forms of gymnosperms appeared and began to actively develop - ginkgos, cycads and conifers.
Rice. 4. Late Paleozoic: 1-coelenterates (single and colonial corals), 2,3-mollusks (2-gastropods, 3-cephalopods (goniatite), 4-brachiopods, 5,6-echinoderms (5-starfish, 6-sea lilies), 7-9-fish (7-finned, 8-shelled, 9-cartilaginous), 10-amphibian; 11-13-reptiles (11-pelycosaurus, 12-pareiasaurus, 13-inostracevia), 14-18-plants (14-psilophyte, 15-articulate (calamites), 16-lycophytes (lepidodendrons and sigillaria), 17-fern, 18-cordite).
In the animal world, the class of reptiles is intensively developing: the very first, cotylosaurs, became the predecessors of all other forms of reptiles. First of all, the lizards (pelycosaurs, which had a large skin ridge to regulate body temperature). A little later, they were replaced by therapsids (probable ancestors of mammals), combining in their structure the characteristics of amphibians, reptiles and mammals, as well as archosaurs (ancient lizards). At the end of the Permian period, the most significant extinction event in the history of the Earth occurred - about 90-95% of animal and plant species disappeared: large marine mollusks, trilobites, giant fish (reaching a length of 15 m), armored animals, large insects and arachnids became extinct. Many amphibians also died, after which they were never again a large group. In Fig. 4 animal and plant worlds of the second half of the Paleozoic era.
^ Mesozoic era: Triassic and Jurassic periods (from 251 to 145 million years ago)
The Triassic period in Earth's history marked the beginning of the Mesozoic era, or "era of middle life." Before him, all the continents were merged into a single giant supercontinent, Pangea. With the onset of the Triassic, Pangea began to gradually break apart, and the mountain-building processes that began in the Permian continue. The climate in those days was equal across the globe. At the poles and at the equator, weather conditions were much more similar than they are today. Towards the end of the Triassic, the climate became drier. Lakes, rivers and vast inland seas began to dry up quickly, and salt and gypsum deposits are now being found in their place. Vast deserts formed in the interior regions of the continents.
The era of dominance of gymnosperms began, which included cycads, similar to ferns and palms, conifers (fir, cypress, yew), ginkgo and benettidaceae - the predecessors of angiosperms. All these plants formed dry forests. In the seas, ammonites, belemnites (the ancestors of modern octopuses, cuttlefish and squids), more advanced six-rayed corals, echinoderms, sharks and ray-finned fish that migrated from fresh water bodies became widespread, and bivalves appeared and multiplied. On land, a variety of insects develop, including flying ones; in place of extinct ancient amphibians, the first representatives of modern amphibians “come” - tailless (frogs, toads), tailed (newts and salamanders), legless (caecilians - creatures similar to earthworms 1.5 in length m) and the already extinct Albanepretons. Modern representatives of these organisms appeared 50-70 million years ago.
The Mesozoic period was also an era of prosperity for reptiles. They gradually conquered all three elements: water, land, and air. At this time (starting 220 million years ago) a wide variety of reptiles appeared. Archosaurs gave rise to several evolutionary lines: the early extinct thecodonts, existing today (three families in total) crocodiles, pterosaurs (flying reptiles) and dinosaurs, the latter being divided into two subgroups - lizard hippies (they are divided into herbivorous - sauropods - and carnivorous - theropod - forms) and ornithischians, which were vegetarians. In parallel with them, the descendants of cotylosaurs developed - turtles, which appeared on Earth 210 million years ago and have survived to this day, marine reptiles (dolphin-like ichthyosaurs and plesiosaurs, resembling a cross between a crocodile, a seal and a giraffe), beaked heads (only one species has survived, living in New Zealand, - hatteria), scaly (various lizards and snakes) and animal-like (therapsids). From small therapsids, approximately 225 million years ago, primitive mammals evolved that resemble small rodents (shrews and hedgehogs) and throughout the Mesozoic, developing, did not exceed the size of a cat. Later, they were replaced by monotremes (proto-beasts), which combine the qualities of reptiles and animals; to date, only 3 species of such animals have survived in Australia - the platypus and 2 species of echidna.
During the Jurassic period, the climate became warm and humid, fairly even, and extensive swamps and lakes formed. Ferns predominated in damp and shady places. About 80% of the planet's flora at this time were gymnosperms. And in the fauna of that time, the most widespread were reptiles, which reached truly record-breaking gigantic sizes. Among them were brontosaurs and diplodocus, who lived on the banks of reservoirs and reached 25-30 meters in length and 20 tons in mass, and predatory bipedal tyrannosaurs up to 15 meters long. Their habitats were dominated by flying lizards (pterosaurs) with a wingspan of up to 12 m and ichthyosaurs up to 20 m long. About 150 million years ago, ancient birds evolved from one of the forms of predatory dinosaurs, which developed in several directions throughout the Cretaceous period. The most famous and well-described (10 skeletons) representative of ancient birds is Archeopteryx (which means “ancient feather”), the first skeleton of which was found in 1861, several years after the advent of Darwin’s theory of evolution.
^ Mesozoic era: Cretaceous period (from 145 to 65 million years ago)
During this period, the surface of our planet began to take on a modern appearance: North America separated, the disintegration of Gondwana continued, and independent South America, Africa, Australia, and Antarctica appeared. In the center of the Indian Ocean was the Hindustan plate. Between the southern continents and Eurasia there remained the ancient Tethys Ocean. The name of the period is associated with the discovery of sedimentary deposits of white chalk on all continents, which is the most characteristic rock of that time. Mountain-building processes took place in western America and eastern Asia.
In the middle of the period, many land areas were flooded.
In the Early and Middle Cretaceous, a wide variety of specialized forms of reptiles arose: stegosaurs, pterodactyls, mosasaurs, etc. The spread of birds began, which still had teeth, like reptiles. In the middle of the Cretaceous, the first flowering (angiosperm) plants appeared, originating probably from some benettid-like ancestors no more than 150 million years ago. They quickly developed and adapted to various natural conditions. About 90 million years ago, flowering plants divided into two classes - dicotyledons (which are now the majority) and monocotyledons (50 thousand species in total, including cereals). At the end of the period, new, more advanced forms of mammals appeared - marsupials and placentals. At the border of the Mesozoic and Cenozoic, a global catastrophe occurred (most likely the fall of a large meteorite, the crater of which was found in North America on the Yucatan Peninsula.). At this time, 75% of all species inhabiting the planet became extinct - all dinosaurs, pterosaurs, all ancient birds (with the exception of the ancestors of modern fan-tailed birds), marine reptiles, large mollusks (ammonites and belemnites), corals, planktonic organisms, the vast majority of gymnosperms (therefore in Currently, this group of plants is represented only by conifers, cycads and the only surviving relict species of ginkgo).
The main representatives of living organisms of the Mesozoic era are shown in Fig. 5.
Rice. 5. Life in the Mesozoic: 1-six-rayed corals, 2-echinoderms, 3-6-mollusks (3-bivalves, 4-gastropods, 5-ammonites, 6-belemnites), 7-archeopteryx, 8-11-terrestrial dinosaurs (8 -stegosaurus, 9-diplodocus, 10-triceratops, 11-tyrannosaurus), 12-13-aquatic dinosaurs (12-plesiosaur, 13-ichthyosaur), 14,15-flying dinosaurs - pterosaurs (14-rhamphorhynchus, 15-pteronodon), 16 - ferns, 17 - benenetites, 18 - cycads, 19 - ginkgos, 20 - gymnosperms.
^ Cenozoic era: Paleogene period (from 65 to 24.6 million years ago)
The Paleogene marked the beginning of the Cenozoic era. At that time, the continents were still in motion as the "great southern continent" Gondwana continued to break apart. South America was now completely cut off from the rest of the world and turned into a kind of floating “ark” with a unique fauna of early mammals. Africa, India and Australia have moved even further away from each other. Throughout the Paleogene, Australia was located near Antarctica. Sea levels dropped and new land masses emerged in many areas of the globe.
The beginning of the Cenozoic era is associated with the great Alpine mountain building (almost all the highest mountain systems in the world arose around this time). During the Cenozoic era, several continental glaciations occurred, covering vast areas (especially in the northern hemisphere).
At the beginning of the Paleogene, a tropical and subtropical climate developed over most of the planet. In the first half of this period, the tropical so-called Poltava flora was formed in Europe, which replaced gymnosperms and was represented by various palm trees (sabal, nipa), ferns, ficus, magnolias, laurels, cinnamon trees, myrtles, etc. Conifers (yews and sequoias) also continued to develop ). Forests and woodlands were widespread. It is no coincidence that most of the animals were forest dwellers. Marsupials and placental mammals evolved in parallel. However, the first ones survived only in Australia, certain islands of the Pacific Ocean and a little in South America. This is due to the fact that these continents separated from the rest early, when placentals had not yet developed there. Among the latter, carnivores arose from insectivores, and ungulates evolved to eat various plant foods, which became a wide variety of mammals; they include equids (which appeared 55 million years ago, spread widely, but are mostly extinct and are now represented by only three families - horses, tapirs and rhinoceroses), artiodactyls (currently thriving and very diverse - hippos, camels, giraffes, deer, pigs, etc.), proboscideans (appeared a little later and formed several different forms (dinotherium, mammoths), but only two genera survived - African and Indian elephants), cetaceans (whales, dolphins), sirens (which are now on the verge of extinction), etc. Among marine animals, it is worth noting the spread of new forms of mollusks (including giant octopuses and squids), sea urchins, crustaceans (crabs, lobsters), and bony fish.
In the second half of the Paleogene, the climate becomes more continental (the first ice caps appear in the Arctic and Antarctic). The Poltava flora in Europe is replaced in the north by the Turgai flora, represented by deciduous species: oaks, beeches, birches, alders, poplars, maples, as well as conifers. Forests gave way to savannas and bushes. The majority of large mammals lived along the banks of rivers and lakes. These were rhinoceroses, tapirs, brontotheres, huge indicatheriums (more than 8 m in length), giant predatory pigs (entelodons - more than 3 m in length), big-horned deer (hornspan 3 m). The history of the development of equids is interesting; their ancestor was Hyracotherium, the size of a dog; in Tertiary times they lived mainly in North America, but later they died out there and were brought back there only during the settlement of America by Europeans. In the Cenozoic era (later 60 million years ago), following the spread of herbivorous animals, predators appeared and multiplied, which included insectivores (moles, bats), mustelids (sea otters, badgers), bears, and pinnipeds (seals, sea lions ), and mongooses (snake hunters), and hyenas (scavengers). But the most characteristic of them are felines and wolves. They could hunt the largest animals thanks to the appearance of powerful fangs up to 20 cm long (saber-toothed cats, for example, Smilodon). The world of modern birds that appeared 65-60 million years ago was very diverse - rheas (ostriches), cranes (cranes, bustards), Anseriformes (geese, ducks, swans, etc.), owls (owls, eagle owls). This was facilitated by the existence of many insects , fruits and seeds of flowering plants. Due to the absence of serious enemies, diatrymas existed - large running birds of prey up to 2.5 m tall, owls 1 m tall, pelicans with a wingspan of 6 m. 60-55 million years ago, a new stage in the development of amphibians began, snakes and lizards developed, widespread received rodents (2000 species), the number of which now accounts for about half of all mammals. These include squirrels (squirrels and beavers), dormouse, mouse-like (hamsters, voles, mice and rats, the last two forms emerging only in the middle of the Neogene), porcupines, pigs and a separate, more ancient order of lagomorphs.
Cenozoic era: Neogene period (from 24.6 to 2.6 million years ago)
During the Neogene, the continents were still “on the march”, and during their collisions a number of grandiose cataclysms occurred. Africa "crashed" into Europe and Asia, resulting in the appearance of the Alps. When India and Asia collided, the Himalayan mountains rose up. At the same time, the Rocky Mountains and Andes formed as other giant plates continued to shift and slide on top of each other. However, Australia and South America remained isolated from the rest of the world, and each of these continents continued to develop its own unique fauna and flora.
In the Neogene, forest and meadow shrub vegetation is replaced by steppe and savanna vegetation, and the first semi-deserts and deserts are formed. Grass and sedge communities appear; trees and shrubs are found in the form of islands of hazel, birch, walnut, juniper, ash, maple, pine, etc.; willows, poplars, and alders grow along the banks of rivers and lakes. At this time, animals - inhabitants of open spaces (the so-called Hipparion fauna) became especially widespread: primitive horses (Hipparions), antelopes, giraffes, bulls, elephants (a wide variety), rhinoceroses, which became victims of saber-toothed cats (Mahairodus, and later - Smilodon ), hyenas, bears and primitive wolves. Giant running birds are widespread, as are vultures, condors, corvids, anseriformes and others. The Neogene marks a wide variety of primates, which appeared about 60 million years ago and the beginning of the development of anthropoids. Now about 200 species of monkeys are known: prosimians (lemurs, tarsiers), lower apes (broad-nosed monkeys in South America and marmosets in the Old World), anthropoids (chimpanzees, gorillas, orangutans) and related hominids (humans). They all have common features - one pair of mammary glands, nails instead of claws, an opposable thumb, forward-looking eyes, a highly developed brain and behavior. Apes emerged 20-25 million years ago. Their ancient extinct representatives were Dryopithecus (ancestors of gorillas), Sivapithecus (ancestors of orangutans and gibbons), Oreopithecus and Ouranopithecus - ancestors of chimpanzees and hominids. In Fig. Figure 6 shows the main animals and plants characteristic of the Cenozoic era.
Rice. 6. Living organisms of both Paleogene and Neogene: 1-six-rayed corals, 2.3 mollusks (2-bivalves, 3-gastropods), 4-crustaceans (crab), 5.6-fish (5-bones, 6-cartilaginous - shark ), 7-birds (Anseri), 8-13-mammals (8-artiodactyls (Eohippus), 9-saber-toothed tiger (Smilodon), 10-oddactyls (Hipparion), 11-indicatherium 12-dinotherium, 13-lemur), 14 - palm trees, 15-coniferous, 16-flowering plants (oaks).
Cenozoic era: Anthropocene period (from 2.6 million years ago to the present day)
At the beginning of the period, most of the continents occupied the same location as today, and some of them needed to cross half the globe to do this. A narrow land bridge connected North and South America. Australia was located on the opposite side of the Earth from Britain. Giant ice sheets were creeping across the northern hemisphere. The world was in the grip of a great glaciation that ended 10,000 years ago. The climate warmed, the glaciers retreated (their remnants are now represented by ice caps in the Arctic and Antarctic), and the time came for the heyday of the human race.
Rice. 7. Life in the Anthropocene: 1,2-mollusks (1-gastropods, 2-cephalopods - squid), 3-fish, 4,5-cetaceans (4-whale, 5-dolphin), 6-great-horned deer, 7-mammoth , 8-rhinoceros, 9-cave bear, 10-homo sapiens, 11-bird, 12-flowering plants - birch, 13-coniferous plants - spruce and pine.
In Eurasia, due to glaciation, tundra and taiga vegetation was widespread (up to France, Northern Spain, Italy, etc.) For Europe, three periods of glaciation are distinguished: Likhvin, Dnieper and Valdai. The fauna was represented by bison, cave bears, mammoths, woolly rhinoceroses, etc. (the so-called mammoth fauna). About 2 million years ago, Homo habilis first appeared (East Africa) and the development of hominids began, which are represented by three successive fossil forms of humans - habilis, erectus and sapiens. The flora and fauna have acquired a modern appearance. Rice. 7 represents animals and plants modern to ancient man, and in Fig. 8 the main stages of anthropogenesis and the features of each of them in the biological and social development of man.
Rice. 8. The main stages of human evolution.
Future of the Earth
Scientists are considering scenarios for the further development of our planet and life on it. They depend on specific phenomena that can influence the development of the Earth.
1) Firstly, the lifetime of our Sun is not infinite; in about 4-5 billion years it will run out of hydrogen fuel. It will expand to the size of a red giant and “swallow” all the nearby planets of the solar system. This is the most likely process, but it will not happen very soon.
2) Active human activity can lead to serious changes. Already now, humans can change some ecological systems and influence geological processes. And the use of nuclear weapons can lead to irreparable consequences when the relationships between different geographical areas are seriously disrupted.
3) It is quite possible that the Earth will collide with a cosmic body - an asteroid or comet. In this case, depending on the size of the object falling on Earth, a catastrophe of a regional or global nature may occur. A typical example of such an event is
Remember how living bodies of nature - organisms - differ from inanimate bodies. What chemical elements do organisms consist of?
Rice. 236. Francesco Redi (1626-1698) and his experience
The question of the emergence of the biosphere is inextricably linked with another question - how did life appear on Earth? This question is the most difficult in science. Life is a planetary phenomenon, so scientists of various specialties - biologists, physicists, chemists, philosophers - are busy searching for an answer to it. There are several theories about the origin of life on Earth, and therefore the biosphere. Let's look at some of them.
Theories of the origin of life on Earth. According to the above-mentioned theory of creationism, life on Earth was created by God as a one-time act (Fig. 235). The beliefs of the supporters of this theory are based on faith. Creationism does not put forward any scientific evidence and has nothing to do with science.
The theory of spontaneous generation of life states that living things are capable of arising from non-living things under certain conditions. Refutations of this were obtained in the experiments of the Italian physician Francesco Redi (Fig. 236).
In 1668, he conducted an experiment using several wide-necked jars in which he placed dead snakes. He covered some of the cans with thick cloth, leaving others open. Soon the flies swooped in and laid eggs on the dead snakes in open jars, from which the larvae then emerged. There were no larvae in the jars covered with cloth, since the flies could not penetrate them and lay eggs (Fig. 236). Consequently, F. Redi concluded, the larvae arose from eggs laid by flies, and did not spontaneously arise from dead snakes, as was commonly believed at that time.
Rice. 235. Michelangelo Buonarrott. World creation. God creates planets. Fragment of the painting of the Sistine Chapel in the Vatican
According to the theory of panspermia (from the Greek pan - everything and sperm - seeds), life on Earth is of extraterrestrial, i.e. cosmic origin. Active supporters and developers of this theory of the origin of life were the Swedish chemist Svante August Arrhenius (Fig. 237) and V.I. Vernadsky.
Rice. 237. Svante August Arrhenius (1859-1927)
The embryos of simple organisms, such as bacteria, the so-called “seeds of life,” according to the theory of panspermia, fall to Earth along with meteorites and cosmic dust (Fig. 238). And then they give rise to life. This assumption is based on the resistance of some bacterial spores to solar radiation, space vacuum and low temperatures. Based on the theory of panspermia, it is possible to assume the existence of organisms on other planets that have suitable conditions for this.
Rice. 238. 1 - meteorite from Mars; 2 - Bacteria-like organic forms found in meteorite cracks
The theory of biopoiesis (from the Greek bios - life and poiesis - formation) considers the emergence of living things on Earth as a result of the chemical evolution of inorganic carbon compounds. This theory is generally accepted in modern science. According to it, the emergence of life on any planet is inevitable if two necessary conditions for this are created and exist for a sufficiently long time - certain inorganic compounds and energy sources. This theory distinguishes three stages in the emergence of life: 1) synthesis of organic compounds from inorganic ones; 2) formation of biological polymers from organic monomers; 3) formation of membrane structures and the first cells from biological polymers.
Chemical evolution and appearance of probionts. The Earth and other planets of the Solar System were formed about 5 billion years ago from a gas and dust cloud consisting of atoms of hydrogen, helium, carbon, oxygen, nitrogen and phosphorus (Fig. 239). As it rotated, the cloud flattened and heated up, resulting in the formation of the Sun and planets. The subsequent cooling of the Sun and planets led to the formation of their structures. Thus, the Earth formed a crust, mantle, core and primary atmosphere, consisting of methane, ammonia, carbon dioxide, carbon monoxide, hydrogen and water vapor. There was no oxygen in the Earth's primary atmosphere. Thanks to the condensation of water vapor, the primary ocean was formed.
Rice. 239. Gas and dust cloud of primary cosmic matter
Due to electrical energy in oxygen-free conditions on Earth, the synthesis of organic compounds - proteins from inorganic ones - could then begin. This hypothesis was put forward in 1924 by the Russian scientist Alexander Ivanovich Oparin (Fig. 240). His assumption subsequently received experimental confirmation.
Rice. 240. Alexander Ivanovich Oparin (1894 - 1980)
In 1953, American scientists Stanley Miller and Harold Urey constructed an installation in which the conditions of the ancient Earth, its primary atmosphere and ocean were reproduced (Fig. 241). In a reaction flask, an electric discharge with a power of 60,000 volts, equivalent to the amount of energy received by the Earth in 50 million years, was passed through a mixture of gases (methane, ammonia, hydrogen) and water vapor at a temperature of 80°C. A week later, simple organic compounds were found in the condensate formed during cooling - lactic acid, urea and amino acids.
Rice. 241. Installation for abiogenic synthesis of organic substances by S. Miller and G. Ury
So, the first step on the path of chemical evolution could be the abiogenic (outside of living systems) synthesis of simple organic substances from inorganic substances in the oxygen-free conditions of the ancient Earth.
Rice. 242. Coacervate drops of protein nature
The second step on the path of chemical evolution is the formation of more complex ones from simple organic compounds. So, from monomers, for example amino acids, polymers - proteins - should have been formed (Fig. 242). Scientists are still arguing about the mechanisms of this kind of process and cannot come to a consensus. According to Oparin, this process could occur through coacervation (from the Latin coacervatus - accumulated, collected) - the spontaneous separation of an aqueous solution of amino acids into protein droplets separated from water (Fig. 243).
Rice. 243. Coacervation
The third, final step on the path of chemical evolution was the formation of membrane structures and the first cells from biological polymers. The impetus for this could be the disturbance of the film, consisting of molecules of abiogenically synthesized proteins and lipids, caused by the wind. The film sagged and formed membrane bubbles. The bubbles were blown out by the wind and falling back onto the surface of the film, they were covered with a second membrane (Fig. 244). Thus, apparently, membrane structures similar to the plasma membrane of a cell could be formed.
Rice. 244. Formation of membrane structures from biological polymers
Over millions of years, membranes were improved, which led to the emergence of probionts (from the Latin pro - ahead and the Greek bios - life). They, according to Oparin, can be considered the predecessors of real cells, since complex metabolic processes and the accurate transfer of genetic information have not yet occurred in them. The transition about 3.8-3.5 billion years ago from probionts to real cells, which possessed these most important signs of life, meant the emergence of life and the beginning of biological evolution.
The beginning of the evolution of the biosphere. All organisms currently existing on Earth are inextricably linked with each other and with the inanimate nature surrounding them through close relationships. It is simply impossible to imagine the appearance in the past on our planet of any single first organisms isolated from the environment. Apparently, life on Earth immediately arose in the form of some kind of primary biocenosis, already included in the biogeochemical cycle. This biocenosis united some primitive single-celled organisms that differed in their feeding methods. Among them there must have been autotrophic and heterotrophic organisms - producers, consumers and destroyers of organic substances. The primary biocenosis was connected with the inanimate nature of the ancient Earth into a single biogeocenosis. The further evolution of the biosphere went in the direction of isolating individual organisms from this primary biocenosis, which were then united into other communities.
Thus, only organisms already included in the biogeochemical cycle and energy flow in the biosphere could sustainably exist and evolve on our planet.
Exercises based on the material covered
- How do various theories explain the emergence of life on our planet? Compare them with each other. What are the weaknesses and strengths of various theories of the origin of life on Earth.
- List the main stages of chemical evolution.
- What conditions and chemical compounds were necessary for the abiogenic synthesis of organic compounds from inorganic ones on the ancient Earth?
- When did biological evolution begin on our planet?
- Explain why scientists believe that life on Earth arose immediately in the form of a primary biocenosis.
Initial stages of biological evolution
The appearance of a primitive cell meant the end of the prebiological evolution of living things and the beginning of the biological evolution of life.
The first single-celled organisms to appear on our planet were primitive bacteria that did not have a nucleus, that is, prokaryotes. As already indicated, these were single-celled, nuclear-free organisms. They were anaerobes, because they lived in an oxygen-free environment, and heterotrophs, because they fed on ready-made organic compounds of the “organic broth,” that is, substances synthesized during chemical evolution. Energy metabolism in most prokaryotes occurred according to the fermentation type. But gradually the “organic broth” decreased as a result of active consumption. As it was exhausted, some organisms began to develop ways to form macromolecules biochemically, inside the cells themselves with the help of enzymes. Under such conditions, cells that were able to receive most of the required energy directly from solar radiation turned out to be competitive. The process of formation of chlorophyll and photosynthesis followed this path.
The transition of living things to photosynthesis and the autotrophic type of nutrition was a turning point in the evolution of living things. The Earth's atmosphere began to be “filled” with oxygen, which was poison for anaerobes. Therefore, many unicellular anaerobes died, others took refuge in oxygen-free environments - swamps and, while feeding, released methane rather than oxygen. Still others have adapted to oxygen. Their central metabolic mechanism was oxygen respiration, which made it possible to increase the yield of useful energy by 10–15 times compared to the anaerobic type of metabolism - fermentation. The transition to photosynthesis was a long process and was completed about 1.8 billion years ago. With the advent of photosynthesis, more and more energy from sunlight accumulated in the organic matter of the Earth, which accelerated the biological cycle of substances and the evolution of living things in general.
In an oxygen environment, eukaryotes, that is, single-celled organisms with a nucleus, formed. These were already more advanced organisms with photosynthetic ability. Their DNA was already concentrated into chromosomes, whereas in prokaryotic cells the hereditary substance was distributed throughout the cell. Eukaryotic chromosomes were concentrated in the cell nucleus, and the cell itself was already reproducing without significant changes. Thus, the daughter cell of eukaryotes was almost an exact copy of the mother cell and had the same chance of survival as the mother cell.
Education of plants and animals
The subsequent evolution of eukaryotes was associated with the division into plant and animal cells. This division occurred in the Proterozoic, when the Earth was inhabited by single-celled organisms (Table 8.2).
Table 8.2
The emergence and distribution of organisms in the history of the Earth (according to Z. Brem and I. Meinke, 1999)
From the beginning of evolution, eukaryotes developed dually, that is, they simultaneously had groups with autotrophic and heterotrophic nutrition, which ensured the integrity and significant autonomy of the living world.
Plant cells have evolved in the direction of reducing the ability to move due to the development of a hard cellulose shell, but in the direction of using photosynthesis.
Animal cells have evolved to increase their ability to move and improve their ability to absorb and excrete food products.
The next stage in the development of living things was sexual reproduction. It arose approximately 900 million years ago.
A further step in the evolution of living things occurred about 700–800 million years ago, when multicellular organisms appeared with differentiated bodies, tissues and organs that perform specific functions. These were sponges, coelenterates, arthropods, etc., related to multicellular animals.
Throughout the Proterozoic and at the beginning of the Paleozoic, plants inhabited mainly seas and oceans. These are green and brown, golden and red algae.
Subsequently, many types of animals already existed in the Cambrian seas. Later they specialized and improved. Among the marine animals of that time were crustaceans, sponges, corals, mollusks, trilobites, etc.
At the end of the Ordovician period, large carnivores, as well as vertebrates, began to appear.
Further evolution of vertebrates went in the direction of jawed fish-like animals. In the Devonian, lungfish - amphibians, and then insects - began to appear. The nervous system gradually developed as a consequence of the improvement of forms of reflection.
A particularly important stage in the evolution of living forms was the emergence of plant and animal organisms from water to land and a further increase in the number of species of terrestrial plants and animals. In the future, it is from them that highly organized forms of life arise. The emergence of plants on land began at the end of the Silurian, and the active conquest of land by vertebrates began in the Carboniferous.
The transition to life in the air required many changes from living organisms and presupposed the development of appropriate adaptations. He sharply increased the rate of evolution of life on Earth. Man became the pinnacle of the evolution of living things.
Life in the air has “increased” the body weight of organisms, the air does not contain nutrients, air transmits light, sound, heat differently than water, and the amount of oxygen in it is higher. It was necessary to adapt to all this. The first vertebrates to adapt to living conditions on land were reptiles. Their eggs were supplied with food and oxygen for the embryo, covered with a hard shell, and were not afraid of drying out.
About 67 million years ago, birds and mammals gained an advantage in natural selection. Thanks to the warm-blooded nature of mammals, they quickly gained a dominant position on Earth, which is associated with cooling conditions on our planet. At this time, it was warm-bloodedness that became the decisive factor for survival. It ensured a constant high body temperature and stable functioning of the internal organs of mammals. Viviparity of mammals and feeding of their young with milk was a powerful factor in their evolution, allowing them to reproduce in a variety of environmental conditions. The developed nervous system contributed to a variety of forms of adaptation and protection of organisms.
There was a division of carnivorous animals into ungulates and predators, and the first insectivorous mammals marked the beginning of the evolution of placental and marsupial organisms.
The decisive stage in the evolution of life on our planet was the emergence of the order of primates. In the Cenozoic, approximately 67–27 million years ago, primates split into apes and apes, which are the oldest ancestors of modern humans. The prerequisites for the emergence of modern man in the process of evolution were formed gradually. At first there was a herd lifestyle. It made it possible to form the foundation of future social communication. Moreover, if in insects (bees, ants, termites) biosociality led to the loss of individuality, then in the ancient ancestors of humans, on the contrary, it developed the individual traits of the individual. This was a powerful driving force for the development of the team.
The evolution of life took its next step with the appearance of Homo sapiens (Homo sapiens). It is Homo sapiens who has the ability to purposefully change the world around him, create artificial conditions for his habitat and transform the appearance of our planet.
Evolutionary theory of Charles Darwin
Under evolution (from lat. evolutio– development, deployment) should be understood as a process of long-term, gradual, slow changes leading to fundamental, qualitatively new changes (the formation of other structures, forms, organisms and their species).
The idea of long-term and gradual changes in all species of animals and plants was expressed by scientists long before Charles Darwin. Aristotle, the Swedish naturalist C. Linnaeus, the French biologist J. Lamarck, the contemporary of Charles Darwin, the English naturalist A. Wallace, and other scientists spoke in this spirit at different times.
The undoubted merit of Charles Darwin is not the idea of evolution itself, but the fact that it was he who first discovered the principle of natural selection in nature and generalized individual evolutionary ideas into one coherent theory of evolution. In the development of his theory, Charles Darwin relied on a large amount of factual material, on experiments and the practice of breeding work to develop new varieties of plants and various breeds of animals.
At the same time, Charles Darwin came to the conclusion that from the many diverse phenomena of living nature, three fundamental factors in the evolution of living things clearly stand out, united by a brief formula: variability, heredity, natural selection.
These fundamental principles are based on the following conclusions and observations of the living world:
1. Variability. It is characteristic of any group of animals and plants; organisms differ from each other in many different ways. In nature it is impossible to find two identical organisms. Variability is an integral property of living organisms; it manifests itself constantly and everywhere.
According to Charles Darwin, there are two types of variability in nature - definite and indefinite.
1) Certain variability(adaptive modification) is the ability of all individuals of the same species in some specific environmental conditions to react in the same way to these conditions (food, climate, etc.). According to modern concepts, adaptive modifications are not inherited, and therefore, for the most part, cannot supply material for organic evolution.
2) Uncertain variability(mutations) causes significant changes in the body in a variety of directions. This variability, unlike a certain one, is hereditary in nature, with minor deviations in the first generation increasing in subsequent ones. Uncertain variability is also associated with environmental changes, but not directly, as in adaptive modifications, but indirectly. Therefore, according to Charles Darwin, it is uncertain changes that play a decisive role in evolution.
2. Constant abundance of the species. The number of organisms of each species that are born is greater than the number that can find food and survive; however, the abundance of each species remains relatively constant under natural conditions.
3. Competitive relations of individuals. Since more individuals are born than can survive, there is a constant struggle for existence in nature, competition for food and habitat.
4. Adaptability, adaptability of organisms. Changes that make it easier for an organism to survive in a particular environment give its owners advantages over other organisms that are less adapted to external conditions and die as a result. The idea of “survival of the fittest” is central to the theory of natural selection. 5. Reproduction of “successful” acquired characteristics in offspring. Surviving individuals give birth to offspring, and thus the “successful” positive changes that allowed them to survive are passed on to subsequent generations.
The essence of the evolutionary process is the continuous adaptation of living organisms to various conditions of the natural environment and the emergence of increasingly complex organisms. Therefore, biological evolution is directed from simple biological forms to more complex forms.
Thus, natural selection, which is the result of the struggle for existence, is the main factor of evolution, directing and determining evolutionary changes. These changes become noticeable after passing through many generations. It is in natural selection that one of the fundamental features of living things is reflected - the dialectic of interaction between the organic system and the environment.
The undoubted advantages of Charles Darwin's evolutionary theory also had some disadvantages. Thus, she could not explain the reasons for the appearance in some organisms of certain structures that seem useless; many species lacked transitional forms between modern animals and fossils; ideas about heredity were also a weak point. Subsequently, shortcomings were discovered regarding the main causes and factors of organic evolution. Already in the 20th century. it became clear that Charles Darwin's theory needs further refinement and improvement, taking into account the latest achievements of biological science. This became a prerequisite for the creation of the synthetic theory of evolution (STE).
Synthetic theory of evolution
The achievements of genetics in revealing the genetic code, the successes of molecular biology, embryology, evolutionary morphology, popular genetics, ecology and some other sciences indicate the need to combine modern genetics with the theory of evolution of Charles Darwin. This association gave rise to in the second half of the 20th century. a new biological paradigm - the synthetic theory of evolution. Since it is based on the theory of Charles Darwin, it is called neo-Darwinian. This theory is considered as non-classical biology. The synthetic theory of evolution made it possible to overcome the contradictions between evolutionary theory and genetics. STE does not yet have a physical model of evolution, but is a multifaceted, complex teaching that underlies modern evolutionary biology. This synthesis of genetics and evolutionary teaching was a qualitative leap in both the development of genetics itself and modern evolutionary theory. This leap marked the creation of a new center for the system of biological knowledge and the transition of biology to the modern non-classical level of its development. STE is often called the general theory of evolution, which is a combination of the evolutionary ideas of Charles Darwin, mainly natural selection, with modern results of research in the field of heredity and variability.
The basic ideas of STE were laid down by the Russian geneticist S. Chetverikov back in 1926 in his works on popular genetics. These ideas were supported and developed by American geneticists R. Fisher, S. Wright, English biologist and geneticist D. Haldane and modern Russian geneticist N. Dubinin (1906–1998).
The main prerequisite for the synthesis of genetics with the theory of evolution was biometric and physical and mathematical approaches to the analysis of evolution, the chromosomal theory of heredity, empirical studies of the variability of natural populations, etc.
The supporting point of STE is the idea that the elementary component of evolution is not a species (according to Darwin) or an individual (according to Lamarck), but a population. It is precisely this that is a holistic system of interconnection between organisms, possessing all the data for self-development. It is not just any individual traits or individuals that are subject to selection, but the entire population, its genotype. However, this selection is carried out through changes in the phenotypic characteristics of individual individuals, which leads to the emergence of new characteristics with the change of biological generations.
The elementary unit of heredity is the gene. It is a section of a DNA molecule (or chromosome) that determines the development of certain characteristics of an organism. Soviet geneticist N.V. Timofeev-Resovsky (1900–1981) formulated a position on the phenomena and factors of evolution. It is as follows:
♦ population – an elementary structural unit;
♦ the mutation process is a supplier of elementary evolutionary material;
♦ population waves – fluctuations in the population size in one direction or another from the average number of its individuals;
♦ isolation consolidates differences in the set of genotypes and causes the division of the original population into several independent ones;
♦ natural selection – selective survival with the possibility of leaving offspring by individuals who have reached reproductive age.
The main determining factor of the synthetic theory of evolution is natural selection, which directs the evolutionary process. The purely biological significance of an individual as an organism that has given offspring is assessed by its contribution to the gene pool of the population. The objects of selection in a population are the phenotypes of individual individuals. The phenotype of an individual organism is determined and formed on the basis of the realized genotype information in changing environmental conditions. As a result, from generation to generation, selection by phenotypes leads to selection of genotypes.
Evolution is a single process. In STE there are two levels of evolution: microevolution, taking place at the population-species level in a relatively short time in limited areas, and macroevolution, taking place at the subspecies level, where general patterns and directions in the historical development of living things appear.
Microevolution is a set of evolutionary processes occurring in populations of a species, leading to changes in the gene pools of these populations and to the formation of new species. It occurs on the basis of mutational variability under the strict control of natural selection. The only source of the appearance of qualitatively new characteristics is mutations. Selection is a creative selective factor that directs elementary evolutionary changes along the path of adaptation of organisms to changing environmental conditions. The nature of microevolutionary processes is influenced by changes in population sizes (waves of life), the exchange of genetic information between them, and isolation. Microevolution leads either to a change in the entire gene pool of a species as a whole (phylogenetic evolution), or to their separation from the parental original species as new forms (speciation).
Macroevolution– these are evolutionary transformations that lead to changes in taxa at a higher level than the species (families, orders, classes). It does not have mechanisms characteristic of it and is carried out through the processes of microevolution. Gradually accumulating, microevolutionary processes receive their external expression in the phenomena of macroevolution. Macroevolution is a generalized picture of evolutionary change observed from a broad historical perspective. Therefore, only at the level of macroevolution do general trends, patterns and directions of the evolution of living nature appear that cannot be observed at the microevolutionary level.
Modern concepts of STE indicate that evolutionary changes are random and undirected in nature, since random mutations are the starting material for them. Evolution proceeds gradually and divergently through the selection of small random mutations. In this case, new life forms are formed through major hereditary changes, the right to life of which is determined by natural selection. A slow and gradual evolutionary process can also have an abrupt nature, associated with changes in environmental conditions as a result of bifurcation processes in the development of our planet.
The synthetic theory of evolution is not some kind of canon, a frozen system of theoretical positions. In its possible range, new directions of research are being formed, fundamental discoveries are appearing and will continue to appear, contributing to further knowledge of the evolutionary processes of living things.
According to modern concepts, an important practical task of STE is to develop optimal ways to manage the evolutionary process in conditions of constantly increasing anthropogenic pressure on the natural environment. This theory is used to solve problems of the relationship between man and nature, nature and human society.
However, the synthetic theory of evolution has some controversial issues and difficulties that give rise to non-Darwinian concepts of evolution. These include, for example, the theory of nomogenesis, the concept of punctualism and some others.
The theory of nomogenesis was proposed in 1922 by the Russian biologist L. Berg. It is based on the idea that evolution is an already programmed process of realizing certain internal patterns inherent in living things. A living organism is inherent in a certain internal force of nature, which always acts, regardless of external conditions, purposefully in the direction of complicating living structures. In support of this, L. Berg pointed to some data on the convergent and parallel evolution of some groups of plants and animals.
One recently emerged non-Darwinian concept is punctualism. Supporters of this direction believe that the process of evolution proceeds spasmodically - through rare and rapid leaps, which account for only 1% of evolutionary time. The remaining 99% of the time of its existence the species remains in a state of stability. In extreme cases, the leap to a new species can occur in small populations of as few as ten individuals over the course of one or more generations. This concept is based on the genetic basis laid down by molecular genetics and modern biochemistry. Punctualism rejects the genetic-population model of speciation, Charles Darwin’s idea of varieties and subspecies as emerging species. Punctualism focused its attention on the molecular genetics of the individual as the bearer of the properties of the species. The idea of the disunity of macro- and microevolution and the independence of the factors controlled by them gives this concept a certain value.
It is likely that in the future a unified theory of life may emerge that combines the synthetic theory of evolution with non-Darwinian concepts of the development of living nature.
Evolutionary picture of the world. Global evolutionism
The idea of world development is the most important idea of world civilization. In its far from perfect forms, it began to penetrate natural science back in the 18th century. But already in the 19th century. can safely be called the century of evolutionary ideas. At this time, development concepts began to penetrate geology, biology, sociology and the humanities. In the first half of the 20th century. science recognized the evolution of nature, society, and man, but there was still no philosophical general principle of development.
And only by the end of the 20th century, natural science acquired a theoretical and methodological basis for creating a unified model of universal evolution, identifying universal laws of direction and driving forces of the evolution of nature. Such a basis is the theory of self-organization of matter, representing synergetics. (As mentioned above, synergetics is the science of the organization of matter.) The concept of universal evolutionism, which reached the global level, linked into a single whole the origin of the Universe (cosmogenesis), the emergence of the Solar system and planet Earth (geogenesis), and the emergence of life (biogenesis) , man and human society (anthroposociogenesis). This model of the development of nature is also called global evolutionism, since it is precisely this model that embraces all existing and mentally imaginable manifestations of matter in a single process of self-organization of nature.
Global evolutionism should be understood as the concept of the development of the Universe as a natural whole developing over time. At the same time, the entire history of the Universe, starting from the Big Bang and ending with the emergence of humanity, is considered as a single process, where the cosmic, chemical, biological and social types of evolution are successively and genetically closely interconnected. Cosmic, geological and biological chemistry in a single process of evolution of molecular systems reflects their fundamental transitions and the inevitability of transformation into living matter. Consequently, the most important regularity of global evolutionism is the direction of the development of the world as a whole (universum) towards increasing its structural organization.
The idea of natural selection plays an important role in the concept of universal evolutionism. Here, something new always arises as a result of the selection of the most effective formations. Ineffective new growths are rejected by the historical process. A qualitatively new level of organization of matter is “affirmed” by history only when it turns out to be able to absorb the previous experience of the historical development of matter. This pattern is especially pronounced for the biological form of motion, but it is characteristic of the entire evolution of matter in general.
The principle of global evolutionism is based on an understanding of the internal logic of the development of the cosmic order of things, the logic of the development of the Universe as a single whole. For such an understanding, an important role is played anthropic principle. Its essence is that the consideration and knowledge of the laws of the Universe and its structure is carried out by a reasonable person. Nature is what it is only because there is a person in it. In other words, the laws of construction of the Universe must be such that it will certainly someday give birth to an observer; if they were different, there would simply be no one to know the Universe. The anthropic principle points to the internal unity of the laws of the historical evolution of the Universe and the prerequisites for the emergence and evolution of living matter up to anthroposociogenesis.
The paradigm of universal evolutionism is a further development and continuation of various ideological pictures of the world. As a result, the very idea of global evolutionism has a worldview character. Its main goal is to establish the direction of the processes of self-organization and development of processes on the scale of the Universe. In our time, the idea of global evolutionism plays a dual role. On the one hand, it represents the world as an integrity, allows us to comprehend the general laws of existence in their unity; on the other hand, it directs modern natural science towards identifying certain patterns of the evolution of matter at all structural levels of its organization and at all stages of its self-development.