How to study the history of the development of life on earth. The process of development of life on Earth: eras, periods, climate, living organisms
Good day, dear seventh graders!
In this message, we will take a trip to the beginning of time. We will try to see and find out how the Earth developed, what events took place on it millions, or even billions of years ago. What organisms appeared on Earth and how, how they replaced each other, in what ways and with what help evolution took place.
But before we look at new material, test your knowledge on the topic
"C. Darwin on the Origin of Species":
- Forms of the struggle for existence No. 1
- Forms of the struggle for existence No. 2
“Time is a long time,” said James Hutton, and indeed the titanic and amazing transformations that have taken place on our planet took an incredibly long time. Flying on a spaceship about 4 billion years ago in the part of the Universe where our Sun is located today, we would have observed a picture different from the one that astronauts see today. Let us remember that the Sun has its own speed of movement - about two tens of kilometers per second; and then it was in another part of the Universe, and the Earth at that time had just been born...
So, the Earth was just born and was in the initial stage of its development. She was a red-hot little ball, swaddled in swirling clouds, and her lullaby was the roar of volcanoes, the hiss of steam and the roar of hurricane winds.
The earliest rocks that could have been formed during this turbulent infancy were volcanic rocks, but they could not remain unchanged for long, for they were subject to the violent attacks of water, heat and steam. The earth's crust caved in, and fiery lava poured out on them. The traces of these terrible battles are carried by rocks of the Archean era - the most ancient rocks known to us today. These are mainly shales and gneisses that occur in deep layers and are exposed in deep canyons, mines, and quarries.
In such rocks - they were formed about one and a half billion years ago - there is almost no evidence of life.
The history of living organisms on Earth is studied by the remains, imprints and other traces of their life preserved in sedimentary rocks. This is what science does paleontology .
For ease of study and description, all The history of the Earth is divided into periods of time, having different durations and differing from each other in climate, intensity of geological processes, the appearance of some groups of organisms and the disappearance of others, etc.
The names of these periods of time are of Greek origin.
The largest such units are eons, there are two of them - cryptozoic (hidden life) and phanerozoic (manifest life) .
Eons are divided into eras. There are two eras in the Cryptozoic: Archean (the most ancient) and Proterozoic (primary life). The Phanerozoic includes three eras - the Paleozoic (ancient life), the Mesozoic (middle life) and the Cenozoic (new life). In turn, eras are divided into periods, periods are sometimes divided into smaller parts.
According to scientists, planet Earth was formed 4.5-7 billion years ago. About 4 billion years ago, the earth’s crust began to cool and harden, and conditions arose on Earth that allowed living organisms to develop.
No one knows exactly when the first living cell arose. The earliest traces of life (bacterial remains) found in ancient sediments of the earth's crust are about 3.5 billion years old. Therefore, the estimated age of life on Earth is 3 billion 600 million years. Let's imagine that this huge period of time fits within one day. Now our “clock” shows exactly 24 hours, and at the moment of the emergence of life it showed 0 hours. Each hour contained 150 million years, each minute – 2.5 million years.
The most ancient era of the development of life - the Precambrian (Archean + Proterozoic) lasted an incredibly long time: over 3 billion years. (from the beginning of the day until 8 pm).
So what was happening at that time?
By this time, the first living organisms were already in the aquatic environment.
Living conditions of the first organisms:
- food – “primary broth” + less fortunate brothers. Millions of years => the broth becomes more and more “diluted”
- depletion of nutrients
- the development of life has reached a dead end.
But evolution found a way out:
- The emergence of bacteria capable of converting inorganic substances into organic ones with the help of sunlight.
- Hydrogen is needed => hydrogen sulfide is decomposed (to build organisms).
- Green plants obtain it by breaking down water and releasing oxygen, but bacteria do not yet know how to do this. (It is much easier to decompose hydrogen sulfide)
- Limited amount of hydrogen sulfide => crisis in the development of life
A “way out” has been found - blue-green algae have learned to split water into hydrogen and oxygen (this is 7 times more difficult than splitting hydrogen sulfide). This is a real feat! (2 billion 300 million years ago – 9 am)
BUT:
Oxygen is a by-product. Accumulation of oxygen → life threatening. (Oxygen is necessary for most modern species, but it has not lost its dangerous oxidizing properties. The first photosynthetic bacteria, enriching the environment with it, essentially poisoned it, making it unsuitable for many of their contemporaries.)
From 11 a.m., a new spontaneous generation of life on Earth became impossible.
The problem is how to deal with the increasing amount of this aggressive substance?
Victory - the appearance of the first organism that inhaled oxygen - the emergence of respiration.
Textbook for grades 10-11
Chapter XIII. Development of life on Earth
The history of living organisms on Earth is studied by the remains, imprints and other traces of their life preserved in sedimentary rocks. This is the science of paleontology. For convenience of study and description, the entire history of the Earth is divided into periods of time that have different durations and differ from each other in climate, intensity of geological processes, the appearance of some groups of organisms and the disappearance of others, etc. In the geological record, these periods of time correspond to different layers of sedimentary rocks with fossil remains included. The deeper a layer of sedimentary rock is located (unless, of course, the layers are turned over as a result of tectonic activity), the older the fossils found there are. This determination of the age of finds is relative. In addition, we must remember that the origin of this or that group of organisms occurs earlier than it appears in the geological record. The group must become large enough so that hundreds of millions of years later we can find its representatives during excavations.
Rice. 71. History of the development of life on Earth and the formation of the modern atmosphere
The names of these periods of time are of Greek origin. The largest such divisions are zones, there are two of them - cryptozoic (hidden life) and phanerozoic (manifest life). Zones are divided into eras (Fig. 71). There are two eras in the cryptozoic - Archean (the most ancient) and Proterozoic (primary life). The Phanerozoic includes three eras - the Paleozoic (ancient life), the Mesozoic (middle life) and the Cenozoic (new life). In turn, eras are divided into periods, periods are sometimes divided into smaller parts. In order to find out what real time periods correspond to eras and periods, the content of isotopes of various chemical elements in rocks and remains of organisms is determined. Since the decay rate of isotopes is a strictly constant and well-known value, the absolute age of the found fossils can be determined. The further a period of time is from us, the less accurately its age is determined.
§ 55. Development of life in the cryptozoic
According to scientists, planet Earth was formed 4.5-7 billion years ago. About 4 billion years ago, the earth’s crust began to cool and harden, and conditions arose on Earth that allowed living organisms to develop. These first organisms were single-celled and did not have hard shells, so it is very difficult to detect traces of their vital activity. It is not surprising that scientists have long believed that the Earth was a lifeless desert for much of its existence. Although the cryptozoic accounts for about 7/8 of the entire history of the Earth, intensive study of this zone began only in the middle of the 20th century. The use of modern research methods, such as electron microscopy, computed tomography, and molecular biology methods, has made it possible to establish that life on Earth is much older than previously thought. Currently, science does not know any sedimentary rocks in which there would be no traces of life activity. In the oldest known sedimentary rocks on Earth, which are 3.8 billion years old, substances were discovered that apparently were part of living organisms.
Archaea. The Archean is the most ancient era, began more than 3.5 billion years ago and lasted about 1 billion years. At this time, cyanobacteria were already quite numerous on Earth, the fossilized waste products of which - stromatolites - were found in significant quantities. Australian and American researchers also found fossilized cyanobacteria themselves. Thus, a kind of “prokaryotic biosphere” already existed in the Archean. Cyanobacteria usually require oxygen to survive. There was no oxygen in the atmosphere yet, but they apparently had enough oxygen, which was released during chemical reactions that took place in the earth's crust. Obviously, a biosphere consisting of anaerobic prokaryotes existed even earlier. The most important event of the Archean was the emergence of photosynthesis. We do not know which organisms were the first photosynthetics. The earliest evidence of photosynthesis comes from carbon-containing minerals with isotope ratios that are specific to the carbon that went through photosynthesis. These minerals are over 3 billion years old. The emergence of photosynthesis was of great importance for the further development of life on Earth. The biosphere received an inexhaustible source of energy, and oxygen began to accumulate in the atmosphere (see Fig. 71). The oxygen content in the atmosphere remained low for a long time, but the prerequisites appeared for the rapid development of aerobic organisms in the future.
Proterozoic. The Proterozoic era is the longest in the history of the Earth. It lasted about 2 billion years. About 600 million years after the start of the Proterozoic, about 2 billion years ago, the oxygen content reached the so-called “Pasteur point” - about 1% of its content in the atmosphere today. Scientists believe that this oxygen concentration is sufficient to ensure the sustainable functioning of single-celled aerobic organisms. A slow but constant increase in oxygen content in the atmosphere contributed to the improvement of cellular respiration and the emergence of oxidative phosphorylation. Oxidative phosphorylation, being a much more efficient way of utilizing carbohydrate energy than anaerobic glycolysis, in turn led to the prosperity of aerobic organisms. The accumulation of oxygen in the atmosphere led to the formation of an ozone screen in the stratosphere, which made life on land fundamentally possible, protecting it from deadly hard ultraviolet radiation. Prokaryotes - bacteria and unicellular algae - apparently also lived on land, in films of water between mineral particles in areas of partial flooding near reservoirs. The result of their life activity was the formation of soil.
Rice. 72. Flora and fauna of the late Proterozoic.
1 - multicellular algae; 2 - sponge; 3 - jellyfish; 4 - crawling annelid worm; 5 - sessile annelid worm; 6 - eight-ray coral; 7 - primitive arthropods of unclear systematic position
An equally important event was the emergence of eukaryotes. When it happened is unknown, since it is very difficult to record it. Research at the molecular level has led some scientists to believe that eukaryotes may be as ancient as prokaryotes. In the geological record, signs of eukaryotic activity appeared approximately 1.8-2 billion years ago. The first eukaryotes were single-celled organisms. Apparently, they have already formed such fundamental characteristics of eukaryotes as mitosis and the presence of membrane organelles. The emergence of one of the most important aromorphoses - sexual reproduction - dates back to 1.5-2 billion years ago.
The most important stage in the development of life was the emergence of multicellularity. This event gave a powerful impetus to the increase in the diversity of living organisms and their evolution. Multicellularity makes possible the specialization of cells within one organism, the emergence of tissues and organs, including sensory organs, active acquisition of food, and movement. These advantages contributed to the wide distribution of organisms, the development of all possible ecological niches and ultimately the formation of the modern biosphere, which replaced the “prokaryotic” one. The first multicellular organisms appeared in the Proterozoic at least 1.5 billion years ago. However, some scientists believe that this happened much earlier - about 2 billion years ago. It was apparently algae.
An explosion of animal diversity. The end of the Proterozoic, approximately 680 million years ago, was marked by a powerful explosion in the diversity of multicellular organisms and the appearance of animals (Fig. 72). Before this period, finds of metazoans are rare and are represented by plants and possibly fungi. The fauna that emerged at the end of the Proterozoic was called Ediacaran from the area in South Australia, where in the middle of the 20th century. The first animal prints were discovered in layers 650-700 million years old. Subsequently, similar finds were made on other continents. These finds served as the reason for the identification of a special period in the Proterozoic, called the Vendian (after the name of one of the Slavic tribes that lived on the shores of the White Sea, where many fossil remains of representatives of this fauna were discovered). The Vendian lasted approximately 110 million years. During this short time compared to previous eras, a large number of species of multicellular animals, belonging to the types of coelenterates, worms, and arthropods, arose and achieved significant diversity. Some of these animals were up to 1 m long, apparently they were gelatinous, like jellyfish. A distinctive feature of the animals of the Vendo-Ediacaran fauna is the absence of any skeleton. There were probably no predators to defend against back then.
What is the reason for this outbreak of diversity? Scientists suggest that at the end of the Proterozoic our planet underwent significant upheavals. Hydrothermal activity was very high, mountain building was underway, and glaciations were replaced by climate warming. The oxygen content in the atmosphere has increased. An increase in oxygen content to 5-6% of the modern level was apparently necessary for the successful existence of fairly large multicellular animals. These changes in the habitat obviously led to the emergence of new types and their rapid development. The cryptozoic era, the eon of “hidden life”, covering more than 85% of the entire existence of life on Earth, ended, and a new stage began - the phanerozoic era.
- How is the relative and absolute age of paleontological finds determined?
- What main aromorphoses can be identified in the evolution of unicellular organisms?
- How did the vital activity of living organisms affect changes in the geological shells of the Earth?
- 4. How can we explain the emergence of a wide variety of multicellular animals at the end of the Proterozoic?
The most significant feature of A.I. Oparin’s hypothesis is the gradual complication of the chemical structure and morphological appearance of the precursors of life (probionts) on the way to living organisms.
A large amount of evidence suggests that the environment for the origin of life could have been coastal areas of seas and oceans. Here, at the junction of sea, land and air, favorable conditions were created for the formation of complex organic compounds.
For example, solutions of some organic substances (sugars, alcohols) are highly stable and can exist for an indefinitely long time. In concentrated solutions of proteins and nucleic acids, clots similar to gelatin clots in aqueous solutions can form. Such clots are called coacervate drops or coacervates (Fig. 66). Coacervates are capable of adsorbing various substances. Chemical compounds enter them from solution, which are transformed as a result of reactions occurring in coacervate droplets and released into the environment.
Coacervates are not yet living creatures. They show only external resemblance to such characteristics of living organisms as growth and metabolism with the environment.
Therefore, the appearance of coacervates is considered a stage of prelife development.
Development of life on Earth.
The history of living organisms on Earth is studied by the remains, imprints and other traces of their life preserved in sedimentary rocks. This is the science of paleontology. For convenience of study and description, the entire history of the Earth is divided into periods of time that have different durations and differ from each other in climate, intensity of geological processes, the appearance of some groups of organisms and the disappearance of other groups of organisms, etc.
The names of these periods of time are of Greek origin. The largest such divisions are zones, there are two of them - cryptozoic (hidden life) and phanerozoic (manifest life). Zones are divided into eras (Fig. 67). There are two eras in the cryptozoic - Archean (the most ancient) and Proterozoic (primary life). The Phanerozoic includes three eras - the Paleozoic (ancient life), the Mesozoic (middle life) and the Cenozoic (new life). In turn, eras are divided into periods, periods are sometimes divided into smaller parts.
Cryptose. According to scientists, planet Earth was formed 4.5-7 billion years ago. About 4 billion years ago, the earth’s crust began to cool and harden, and conditions arose on Earth that allowed living organisms to develop. Archaea. The Archean is the most ancient era, began more than 3.5 billion years ago and lasted about 1 billion years. At this time, cyanobacteria were already quite numerous on Earth, the fossilized waste products of which - stromatolites - were found in significant quantities.
Australian and American researchers also found fossilized cyanobacteria themselves. Thus, a kind of “prokaryotic biosphere” already existed in the Archean. Cyanobacteria usually require oxygen to survive. There was no oxygen in the atmosphere yet, but they apparently had enough oxygen, which was released during chemical reactions that took place in the earth's crust.
Obviously, a biosphere consisting of anaerobic prokaryotes existed even earlier.
The most important event of the Archean was the emergence of photosynthesis. We do not know which organisms were the first photosynthetics.
Proterozoic.
The Proterozoic era is the longest in the history of the Earth. It lasted about 2 billion years.
About 600 million years after the beginning of the Proterozoic, about 2 billion years ago, the oxygen content reached the so-called “Pasteur point” - about 1% of its content in the atmosphere today.
Scientists believe that this oxygen concentration is sufficient to ensure the sustainable functioning of single-celled aerobic organisms.
An explosion of animal diversity. The end of the Proterozoic, approximately 680 million years ago, was marked by a powerful explosion in the diversity of multicellular organisms and the appearance of animals (Fig. 68). Before this period, finds of metazoans are rare and are represented by plants and possibly fungi.
The fauna that emerged at the end of the Proterozoic was called Ediacaran from the area in South Australia, where in the middle of the 20th century. The first animal prints were discovered in layers 650-700 million years old.
Subsequently, similar finds were made on other continents. These finds served as the reason for the identification of a special period in the Proterozoic, called the Vendian (after the name of one of the Slavic tribes that lived on the shores of the White Sea, where rich localities of representatives of this fauna were discovered). Paleozoic.
The Paleozoic era is much shorter than the previous ones; it lasted about 340 million years. The land, which at the end of the Proterozoic represented a single supercontinent, split into separate continents, grouped near the equator. This led to the creation of a large number of small coastal areas suitable for the settlement of living organisms. By the beginning of the Paleozoic, some animals had formed an external organic or mineral skeleton.
The Cambrian climate was temperate, the continents were lowland. In the Cambrian, animals and plants inhabited mainly the seas. Bacteria and blue-greens still lived on land.
The Cambrian period was marked by the rapid spread of representatives of new types of invertebrate animals, many of which had calcareous or phosphate skeletons.
Scientists associate this with the emergence of predation. Among single-celled animals, there were numerous foraminifera - representatives of protozoa that had a calcareous shell or a shell glued together from grains of sand.
Ordovician. In the Ordovician, the area of seas increases significantly. In the Ordovician seas, green, brown and red algae are very diverse. There is an intensive process of reef formation by corals.
Significant diversity is observed among cephalopods and gastropods. In the Ordovician, chordates first appeared. Silur. At the end of the Silurian, the development of peculiar arthropods - crustacean scorpions - is observed. The Ordovician and Silurian saw the flourishing of cephalopods in the seas.
New representatives of invertebrates appear - echinoderms. In the Silurian seas, the mass distribution of the first true vertebrates - armored agnathans - began. At the end of the Silurian - beginning of the Devonian, intensive development of land plants began.
Animals also come out onto land.
Among the first to move from the aquatic environment were representatives of the arthropod type - spiders; they were protected from the drying effects of the atmosphere by a chitinous shell. Devonian. As a result of the rise of land and the reduction of seas, the Devonian climate was more continental than in the Silurian. In the Devonian, desert and semi-desert areas appeared. Real fish lived in the seas, replacing the armored jawless fish. Among them were cartilaginous fish (modern representatives are sharks), and fish with a bony skeleton also appeared. In the Devonian, the first forests of giant ferns, horsetails and mosses appeared on land. New groups of animals begin to conquer land.
Representatives of arthropods that came to land give rise to centipedes and the first insects. At the end of the Devonian, the descendants of fish came to land, forming the first class of terrestrial vertebrates - amphibians (amphibians). Carbon. During the Carboniferous period, or Carboniferous, there was a noticeable warming and humidification of the climate. Huge (up to 40 m high) ferns, horsetails and mosses grow in hot, tropical swampy forests.
In addition to these plants, which reproduce by spores, gymnosperms, which arose at the end of the Devonian, begin to spread in the Carboniferous. Their seed was covered with a shell that protected it from drying out. In humid and warm swampy forests, the oldest amphibians - stegocephals - reached exceptional prosperity and diversity.
The first orders of winged insects appear - cockroaches, whose body length reaches 10 cm, and dragonflies, some species of which had a wingspan of up to 75 cm. Perm.
Further uplift of the land led to the development of an arid climate and cooling in the Permian.
Wet and lush forests remain only around the equator; Ferns are gradually dying out. They are replaced by gymnosperms.
The dry climate contributed to the disappearance of amphibians - stegocephalians. But the oldest reptiles, which arose at the end of the Carboniferous, reach significant diversity.
The Mesozoic is rightly called the era of reptiles. Their heyday, widest divergence and extinction occur precisely in this era. Triassic. In the Triassic, the areas of inland water bodies were greatly reduced, and desert landscapes developed. In arid climates, many land organisms whose individual stages of life are associated with water die out.
Most amphibians die out, tree ferns, horsetails and mosses almost completely disappear.
Instead, terrestrial forms begin to predominate, in the life cycle of which there are no stages associated with water. Among plants in the Triassic, gymnosperms reached strong development, and among animals, reptiles. Already in the Triassic, the first representatives of warm-blooded animals appeared - small primitive mammals and birds. Yura. In the Jurassic, there is some expansion of the areas of warm-water seas. In the seas, cephalopods - ammonites and belemnites - are very numerous.
Marine reptiles are very diverse.
In addition to ichthyosaurs, plesiosaurs appear in the Jurassic seas - animals with a wide body, long flippers and a serpentine neck.
Marine reptiles seemed to divide food resources among themselves: plesiosaurs hunted in the shallow waters of the coastal zone, and ichthyosaurs hunted in the open sea. In the Jurassic, reptiles began to master the air environment.
The diversity of flying insects created conditions for the development of insectivorous flying dinosaurs.
Large lizards began to feed on small flying lizards.
Flying lizards survived until the end of the Cretaceous. Chalk.
The Cretaceous period (or chalk) is named due to the formation of chalk in the marine sediments of that time. It arose from the remains of the shells of protozoan animals - foraminifera. During this period, angiosperms appear and spread extremely quickly, and gymnosperms are replaced.
The widespread distribution of insects and the appearance of the first angiosperms led over time to a connection between them. Angiosperms developed a flower - a reproductive organ that attracts insects by color, smell and nectar reserves.
Insects, feeding on nectar, became carriers of pollen.
The transfer of pollen by insects, compared to wind pollination, leads to less waste of gametes. At the end of the Cretaceous, the climate changed towards sharp continentality and general cooling. Ammonites and belemnites die out in the seas, and after them the sea lizards that fed on them - plesiosaurs and ichthyosaurs. On land, moisture-loving vegetation that served as food for herbivorous dinosaurs began to decline, which led to their disappearance; Carnivorous dinosaurs also became extinct. Of the reptiles, large forms have been preserved only in the equatorial regions - crocodiles, turtles and tuataria.
Most of the surviving reptiles (lizards, snakes) were small in size. In conditions of a sharply continental climate and general cooling, exceptional advantages were given to warm-blooded animals - birds and mammals, whose heyday dates back to the next era - the Cenozoic.
Cenozoic.
The Cenozoic era is the flowering of flowering plants, insects, birds and mammals. It began about 66 million years ago and continues to the present day.
Paleogene.
During the first period of the Cenozoic, mammals replaced reptiles, occupying their ecological niches on the ground, and birds began to dominate the air. During this period, most modern groups of mammals were formed - insectivores, carnivores, pinnipeds, cetaceans, and ungulates.
The first primitive primates appeared, lemurs and then real monkeys.
Neogene. During the Neogene, the climate became colder and drier.
Tropical and savanna forests, which once grew in the temperate zone from modern Hungary to Mongolia, are being replaced by steppes. This led to the widespread distribution of cereal plants, which became a source of food for herbivorous mammals. During this period, all modern orders of mammals were formed, and the first apes appeared.
Anthropocene.
The last period of the Cenozoic - the Anthropocene - is the geological period in which we live. Its name is due to the fact that it was during this period that man appeared. In the Anthropocene there are two centuries (not centuries, but centuries in the geological sense) - the Pleistocene and the Holocene. During the Pleistocene, very strong climate changes were observed - four giant glaciations occurred, followed by the retreat of glaciers.
Negative temperatures in the glaciation zone led to the fact that water vapor condensed in the form of snow, and the melting of ice and snow annually produced less water than snowfall.
The accumulation of gigantic ice reserves on land has led to a significant drop in the level of the World Ocean (by 60-90 m). In the Old World (with the exception of Madagascar), humans settled at least 500 thousand years ago, and possibly much earlier. Before the last glaciation (about 35-40 thousand years ago), ancient hunters from Asia crossed a land bridge in the area of the modern Bering Strait to North America, which they settled as far as Tierra del Fuego. By the beginning of the Holocene, when global warming and melting of glaciers began, many large mammals became extinct - mammoths, woolly rhinoceroses, and cave bears. Apparently, this extinction was caused not only by climate change, but also by active human activity. About 10 thousand years ago, in the warm temperate regions of the Earth (Mediterranean, Middle East, India, China, Mexico, Peru, etc.) the “Neolithic Revolution” began, associated with the transition of man from gathering and hunting to agriculture and cattle breeding.
The domestication of animals and the introduction of plants into culture began.
Rapid human activity: plowing of lands, uprooting and burning of forests, grazing pastures and trampling of grass stands by domestic animals - led to the extinction or reduction of the habitats of many steppe animals (tur, tarpan, etc.), to the expansion of desert areas (Sahara, Karakum, Taklamakan ), the appearance of shifting sands. All this determined the species composition of the organic world that currently exists, influenced the modern geographical distribution of organisms, and created their modern communities.
The history of the development of life is studied using data geology And paleontology, since the structure of the earth's crust preserves many fossil remains produced by living organisms. In place of the former seas, sedimentary rocks formed containing huge layers of chalk, sandstones and other minerals, representing bottom sediments of calcareous shells and silicon skeletons of ancient organisms. There are also reliable methods for determining the age of earth rocks containing organic matter. Usually the radioisotope method is used, based on measuring the content of radioactive isotopes in the composition of uranium, carbon, etc., which naturally changes over time.
Let us immediately note that the development of life forms on Earth went in parallel with the geological restructuring of the structure and topography of the earth’s crust, with changes in the boundaries of the continents and the world ocean, the composition of the atmosphere, the temperature of the earth’s surface and other geological factors. These changes determined to a decisive extent the direction and dynamics of biological evolution.
The first traces of life on Earth date back to approximately 3.6–3.8 billion years ago. Thus, life arose soon after the formation of the earth's crust. In accordance with the most significant events of geobiological evolution in the history of the Earth, large time intervals are distinguished - eras, within them - periods, within periods - epochs, etc. For greater clarity, let us depict the calendar of life in the form of a conditional annual cycle, in which one month corresponds to 300 million years of real time (Fig. 6.2). Then the entire period of development of life on Earth will be exactly one conventional year of our calendar - from “January 1” (3600 million years ago), when the first protocells were formed, to “December 31” (zero years), when you and I live . As you can see, geological time is usually counted in reverse order.
(1) Archaea
Archean era(era of ancient life) - from 3600 to 2600 million years ago, the length of 1 billion years - approximately a quarter of the entire history of life (on our conventional calendar these are “January”, “February”, “March” and several days of “April”).
Primitive life existed in the waters of the world's oceans in the form of primitive protocells. There was no oxygen in the Earth’s atmosphere yet, but there were free organic substances in the water, so the first bacteria-like organisms fed heterotrophically: they absorbed ready-made organic matter and obtained energy through fermentation. In hot springs, rich in hydrogen sulfide and other gases, at temperatures up to 120°C, autotrophic chemosynthetic bacteria or their new forms, archaea, could live. As the primary reserves of organic matter were depleted, autotrophic photosynthetic cells emerged. In coastal zones, bacteria reached land and soil formation began.
With the appearance of free oxygen in water and the atmosphere (from photosynthetic bacteria) and the accumulation of carbon dioxide, opportunities are created for the development of more productive bacteria, and after them the first eukaryotic cells with a real nucleus and organelles. From them subsequently developed various protists (single-celled protozoan organisms) and then plants, fungi, and animals.
Thus, in the Archean era, pro- and eukaryotic cells with different types of nutrition and energy supply arose in the world’s oceans. The prerequisites have emerged for the transition to multicellular organisms.
(2) Proterozoic
Proterozoic era(Era of Early Life), from 2600 to 570 million years ago, is the longest era, covering about 2 billion years, that is, more than half of the entire history of life.
Rice. 6.2. Eras and periods of development of life on Earth
Intense mountain building processes have changed the relationship between ocean and land. There is an assumption that at the beginning of the Proterozoic the Earth underwent the first glaciation, caused by a change in the composition of the atmosphere and its transparency to solar heat. Many pioneer groups of organisms, having done their job, died out and were replaced by new ones. But in general, biological transformations took place very slowly and gradually.
The first half of the Proterozoic took place with the full flourishing and dominance of prokaryotes - bacteria and archaea. At this time, iron bacteria of the world's oceans, settling generation after generation to the bottom, form huge deposits of sedimentary iron ores. The largest of them are known near Kursk and Krivoy Rog. Eukaryotes were represented mainly by algae. Multicellular organisms were few in number and very primitive.
About 1000 million years ago, as a result of the photosynthetic activity of algae, the rate of oxygen accumulation rapidly increased. This is also facilitated by the completion of the oxidation of iron in the earth's crust, which until now has absorbed the bulk of the oxygen. As a result, the rapid development of protozoa and multicellular animals begins. The last quarter of the Proterozoic is known as the “age of jellyfish,” since these and similar coelenterates constituted the dominant and most progressive form of life at that time.
About 700 million years ago, our planet and its inhabitants experienced the second ice age, after which the progressive development of life became increasingly dynamic. During the so-called Vendian period, several new groups of multicellular animals were formed, but life was still concentrated in the seas.
At the end of the Proterozoic, triatomic oxygen O 3 accumulates in the atmosphere. This is ozone, which absorbs ultraviolet rays from sunlight. The ozone screen reduced the level of mutagenicity of solar radiation. Further new formations were numerous and varied, but they were less and less radical in nature - within the already formed biological kingdoms (bacteria, archaea, protists, plants, fungi, animals) and main types.
So, during the Proterozoic era, the dominance of prokaryotes was replaced by the dominance of eukaryotes, a radical transition from unicellularity to multicellularity occurred, and the main types of the animal kingdom were formed. But these complex life forms existed exclusively in the seas.
The earth's land at this time represented one large continent; geologists gave it the name Paleopangea. In the future, global crustal plate tectonics and the corresponding continental drift will play a large role in the evolution of terrestrial life forms. While, in the Proterozoic, the rocky surface of the coastal areas was slowly covered with soil, bacteria, lower algae, and simple unicellular animals settled in the damp lowlands, which continued to exist perfectly in their ecological niches. The land was still waiting for its conquerors. And on our historical calendar it was already the beginning of “November”. Before the “New Year”, until our days, there were less than “two months” left, only 570 million years.
(3) Paleozoic
Palaeozoic(era of ancient life) – from 570 to 230 million years ago, total length 340 million years.
Another period of intense mountain building led to a change in the topography of the earth's surface. Paleopangea was divided into the giant continent of the Southern Hemisphere, Gondwana, and several small continents of the Northern Hemisphere. Former areas of land were under water. Some groups went extinct, but others adapted and developed new habitats.
The general course of evolution, starting from the Paleozoic, is reflected in Fig. 6.3. Please note that most directions of the evolution of organisms that originated at the end of the Proterozoic continue to coexist with newly emerging young groups, although many are reducing their volume. Nature parts with those who do not correspond to changing conditions, but retains successful options as much as possible, selects and develops of them are the most adapted and, in addition, creates new forms, among them chordates. Higher plants appear - land conquerors. Their body is divided into a root and a stem, which allows them to be well anchored in the soil and extract moisture and minerals from it.
Rice. 6.3. Evolutionary development of the living world from the end of the Proterozoic to the present time
The area of the seas increases and decreases. At the end of the Ordovician, as a result of a decrease in the level of the world's seas and a general cooling, a rapid and massive extinction of many groups of organisms occurred, both in the seas and on land. In the Silurian, the continents of the Northern Hemisphere unite to form the supercontinent Laurasia, which is shared with the southern continent of Gondwana. The climate becomes drier, milder and warmer. Armored “fish” appear in the seas, and the first articulated animals come to land. With the new rise of land and the reduction of seas in the Devonian, the climate becomes more contrasting. Mosses, ferns, and mushrooms appear on the ground, and the first forests are formed, consisting of giant ferns, horsetails and mosses. Among animals, the first amphibians, or amphibians, appear. In the Carboniferous, swampy forests of huge (up to 40 m) tree ferns are widespread. It was these forests that left us coal deposits (“coal forests”). At the end of the Carboniferous, the land rose and cooled, the first reptiles appeared, finally freed from water dependence. In the Permian period, another uplift of land led to the unification of Gondwana with Laurasia. A single continent, Pangea, was formed again. As a result of the next cold snap, the polar regions of the Earth are subject to glaciation. Tree-like horsetails, mosses, ferns, and many ancient groups of invertebrate and vertebrate animals are dying out. In total, by the end of the Permian period, up to 95% of marine species and about 70% of terrestrial species became extinct. But reptiles (reptiles) and new insects are progressing quickly: their eggs are protected from drying out by dense shells, their skin is covered with scales or chitin.
The overall result of the Paleozoic was the settlement of land by plants, fungi and animals.. At the same time, both of them, and the third, in the process of their evolution become more complex anatomically, acquiring new structural and functional adaptations for reproduction, breathing, and nutrition, which contribute to the development of a new habitat.
The Paleozoic period ends when our calendar says “December 7th”. Nature is “in a hurry”, the pace of evolution in groups is high, the time frame for transformations is compressing, but the first reptiles are just appearing on the scene, and the time of birds and mammals is still far ahead.
(4) Mesozoic
Mesozoic era(era of middle life) - from 230 to 67 million years ago, a total length of 163 million years.
The uplift of land that began in the previous period continues. At first there was a single continent called Pangea. Its total area is significantly larger than the current land area. The central part of the continent is covered with deserts and mountains; the Urals, Altai and other mountain ranges have already been formed. The climate is becoming increasingly arid. Only river valleys and coastal lowlands are inhabited by monotonous vegetation of primitive ferns, cycads and gymnosperms.
During the Triassic, Pangea gradually splits into northern and southern continents. Among the animals on land, herbivores and predatory reptiles, including dinosaurs, begin their “triumphant march.” Among them there are also modern species: turtles and crocodiles. Amphibians and various cephalopods still live in the seas, and bony fish of a completely modern appearance appear. This abundance of food attracts predatory reptiles to the sea, and their specialized branch, the ichthyosaurs, separates. Small groups separated from some early reptiles, giving rise to birds and mammals. They already have an important feature - warm-bloodedness, which will give great advantages in the further struggle for existence. But their time is still ahead, and in the meantime dinosaurs continue to conquer the earth’s spaces.
In the Jurassic period, the first flowering plants appeared, and among the animals giant reptiles dominated, mastering all habitats. In warm seas, in addition to marine reptiles, bony fish and various cephalopods, similar to modern squids and octopuses, thrive. The split and drift of the continents continues with a general direction towards their modern state. This creates conditions for isolation and relatively independent development of fauna and flora on different continents and island systems.
In the Cretaceous period, in addition to oviparous and marsupial mammals, placental mammals appeared, bearing their young for a long time in the mother's womb in contact with blood through the placenta. Insects begin to use flowers as a source of food, while simultaneously contributing to their pollination. This cooperation has benefited both insects and flowering plants. The end of the Cretaceous period was marked by a drop in sea level, a new general cooling and mass extinction of many groups of animals, including dinosaurs. It is believed that 10–15% of the previous species diversity remains on land.
There are different versions of these dramatic events at the end of the Mesozoic. The most popular scenario is a global catastrophe caused by the fall of a giant meteorite or asteroid to Earth and leading to the rapid destruction of the biosphere balance (shock wave, atmospheric dust, powerful tsunami waves, etc.). However, everything could have been much more prosaic. The gradual restructuring of continents and climate change could lead to the destruction of established food chains built on a limited range of producers. First, some invertebrate animals, including large cephalopods, died out in the colder seas. Naturally, this led to the extinction of sea lizards, for which cephalopods were the main food. On land, there was a reduction in the growing area and biomass of soft, succulent vegetation, which led to the extinction of giant herbivores, followed by predatory dinosaurs. The food supply for large insects also decreased, and behind them flying lizards began to disappear. As a result, over several million years, the main groups of dinosaurs became extinct. We must also keep in mind the fact that reptiles were cold-blooded animals and turned out to be not adapted to existence in a new, much more severe climate. Under these conditions, small reptiles - lizards, snakes - survived and developed further; and relatively large ones, such as crocodiles, turtles, and tuateria, survived only in the tropics, where the necessary food supply and mild climate remained.
Thus, the Mesozoic era is rightfully called the era of reptiles. Over 160 million years, they experienced their heyday, widespread divergence across all habitats, and died out in the fight against the inevitable elements. Against the backdrop of these events, warm-blooded organisms - mammals and birds - received enormous advantages, moving on to explore the liberated ecological niches. But this was already a new era. There were “7 days” left until the “New Year”.
(5) Cenozoic
Cenozoic era(era of new life) – from 67 million years ago to the present. This is the era of flowering plants, insects, birds and mammals. In this era, man also appeared.
At the beginning of the Cenozoic, the location of the continents is already close to the modern one, but there are wide bridges between Asia and North America, the latter is connected through Greenland to Europe, and Europe is separated from Asia by a strait. South America was isolated for several tens of millions of years. India is also isolated, although it is gradually moving north towards the Asian continent. Australia, which at the beginning of the Cenozoic was connected with Antarctica and South America, about 55 million years ago completely separated and gradually moved north. On isolated continents, special directions and rates of evolution of flora and fauna are created. For example, in Australia, the absence of predators allowed ancient marsupials and egg-laying mammals, long extinct on other continents, to survive. Geological changes contributed to the emergence of increasing biodiversity, as they created greater variations in the living conditions of plants and animals.
About 50 million years ago, in North America and Europe, a detachment of primates appeared in the class of mammals, which later gave rise to monkeys and humans. The first people appeared about 3 million years ago ("7 hours" before the "New Year"), apparently in the eastern Mediterranean. At the same time, the climate became increasingly cooler, and the next (fourth, counting from the early Proterozoic) ice age began. In the northern hemisphere, four periodic glaciations (like ice age phases alternating with temporary warmings) have occurred over the last million years. During this time, mammoths, many large animals, and ungulates became extinct. People who were actively involved in hunting and farming played a big role in this. The modern human species was formed only about 100 thousand years ago (after “23 hours 45 minutes on December 31” of our conventional year of life; we exist this year for only its last quarter of an hour!).
In conclusion, we emphasize once again that driving forces biological evolution must be seen in two interconnected planes - geological and actually biological. Each successive large-scale restructuring of the earth's surface entailed inevitable transformations in the living world. Each new cold spell led to the mass extinction of poorly adapted species. Continental drift determined the difference in the rates and directions of evolution in large isolates. On the other hand, the progressive development and reproduction of bacteria, plants, fungi and animals also affected geological evolution itself. As a result of the destruction of the mineral basis of the Earth and its enrichment with metabolic products of microorganisms, the soil arose and was constantly rebuilt. The accumulation of oxygen at the end of the Proterozoic led to the formation of the ozone shield. Many waste products remained forever in the bowels of the earth, transforming them irreversibly. These include organogenic iron ores, deposits of sulfur, chalk, coal, and much more. Living things, generated from inanimate matter, evolve along with it, in a single biogeochemical flow of matter and energy. As for the internal essence and direct factors of biological evolution, we will consider them in a special section (see 6.5).
The diversity of the organic world in the present is great, but it will seem literally limitless if you imagine how it happened development of life on Earth for hundreds of millions of years.
Any blade of grass that we pass by indifferently had a very long series of generations of its ancestors, and the further back into the centuries, the less similar these ancestors were to modern forms.Each organism is formed not only under the influence of the present, but also of the entire past, right up to the time of the beginning of life hidden in the darkness.K. A. Timiryazev The picture of the development of the organic world is often visually depicted in the form branchy tree. The trunk of a tree is the primary green organisms, large branches are the groups of still simple plants that arose from them, smaller branches are the changed descendants of these groups, the ends of the branches are modern forms. Family tree. Some branches of this tree have dried up - these are extinct groups that disappeared due to some conditions that turned out to be unfavorable for them; other branches, on the contrary, grew luxuriantly, forming many branches - these are groups of plants that developed in conditions favorable to their life and gave many new forms. Such a visual representation of the history of the development of organisms, showing not only the origin of a particular group of organisms, but also the relationship of different groups, is called family tree. This evolution can be represented even more clearly in the form river movement, divided into numerous channels, sometimes fast and swift, sometimes slow, narrowing and disappearing. Just as in the channels and branches of a real river the amount of water carried away and the speed of its movement constantly change, so the forms of plants of the great river of life also changed: some quickly, others remaining almost unchanged for a long time. Wanting to emphasize this continuous movement of life as its main property, K.A. Timiryazev named biology is the science of the dynamics of the organic world.
Changes on earth
A lot of changes happened on Earth for its centuries-old history:- The contours and relief of land, the area and depth of the world's oceans changed.
- New mountain ranges arose, were destroyed, and mountainous areas turned into plains.
- The direction and nature of winds and sea currents changed.
- The composition of the atmosphere and water of the oceans and seas has also changed over time.
- The amount of light and heat coming to the earth from the sun varied at different times.
- Scientists believe that even the position of the earth's axis in relation to the plane of the earth's movement around the sun did not remain unchanged.
Traces of a past life
The most valuable data on these changes are obtained from the remains of life preserved in the bowels of the earth. These traces of a past life studies science paleontology. It greatly helps geology to figure out what changes took place in. The remains of animals and plants are called paleontological documents, that is, very reliable materials from which one can confidently judge what events took place on Earth in the past. Paleontological documents discovered in the bowels of the earth have long attracted the attention of scientists. For example, M.V. Lomonosov wrote about this in his work “On the Layers of the Earth”:The earth's surface now has a completely different appearance than it did in ancient times. In cold climates, traces of Indian herbs are shown in stone mountains with clear outlines indicating their nature.Thus, based on the fact that traces of southern plants are found in cold countries, Lomonosov made an absolutely correct assumption: obviously, in the distant past, living conditions in the north were completely different than now.
Valuable excavations
Unfortunately, detailed valuable excavations found relatively rarely. After all, there have rarely been such particularly favorable conditions on Earth under which the tender parts of a plant could leave some kind of lasting trace. It sometimes happened that a leaf, falling on soft mud, became covered with it. Subsequently, the silt became compacted, turned into solid rock, and the researcher, splitting such layered rock into plates, suddenly discovered a distinct trace of a leaf or other part of an ancient plant.Amber
Pieces are found on the southern and southeastern coasts amber, and they contain very well-preserved imprints of small arthropods (insects, spiders) and parts of plants (buds, leaves, flowers, seeds, etc.). Amber is the hardened resin of some ancient coniferous trees. When it flowed from their damaged trunks and branches, small animals and parts of plants fell into it.
Amber is the hardened resin of some ancient coniferous trees. Much time passed, the resin turned into amber, and now we sometimes find amazingly clear and precise traces of ancient life in it. Pieces of petrified wood
Found in the ground and pieces of petrified wood, consisting entirely of mineral matter. They preserved the structure of the wood so accurately that a researcher examining thin slices of the fossil under a microscope seems to see the wood of a living tree. Such a fossil is formed under special conditions when the organic matter of the tree is very slowly replaced by mineral substances dissolved in water. As a result, the tree, while maintaining its shape and structure, is completely mineralized.
Mineralized wood. In most cases, very large and painstaking work is required to restore the remaining half-erased traces plant past. Nevertheless, persistent research thought penetrated into the depths of the past and, using these traces, quite fully restored how the plant world changed over millions of centuries. According to these data, the development of life, like the development of everything that exists, was not smooth - there was an alternation of long, relatively calm periods and shorter, but stormy periods. The duration of violent geological revolutions is often determined by millions of years. Nevertheless, such revolutionary periods in the development of life passed much faster than calm, evolutionary periods. Scientists who have studied the development of life on Earth have long noted this unevenness of development based on the qualitatively different layers of sediments and remains of life found in the earth. This is where the division of life history into separate stages arose. The longest periods of time are called eras. Their duration is usually hundreds of millions of years. 
