The history of the evolution of life on earth. Human evolution

Bones of dinosaurs and amazing extinct animals have been found in different eras of human history. In the absence of science, legends about giants or dragons were formed from the bones found. Only the main stages of the development of life on Earth could be studied from paleontological finds. modern people with the development of science.

Earth Education

Our planet was formed about 4.5 billion years ago from stardust and particulate matter. As gravity increased, the Earth began to attract debris and rocks from space, which fell to the surface, gradually warming the planet. Over time, the top layer became denser and began to cool. The hot mantle maintains heat until now, preventing the Earth from turning into a block of ice.

For a long time the planet was in a lifeless state. The atmosphere was filled with various gases and did not contain oxygen. Thanks to the release large quantity steam from the bowels of the Earth and gravity began to form dense clouds. Intense rains contributed to the emergence of the World Ocean, in which life originated.

Rice. 1. Formation of the Earth.

Oxygen appeared in the atmosphere with the appearance of the first photosynthetic plants.

Stages of development

Life on Earth is associated with geological eons and eras. An aeon is a large segment geological history, uniting several eras. In turn, eras are divided into periods. Each era is characterized by individual development of the animal and plant world, which often depended on climate, condition earth's crust, underground activities.

Rice. 2. Eras of the geological history of the Earth.

A more detailed description of the eons is presented in the table of the main stages of the development of life on Earth.

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There are a huge number of theories about the origin of life on Earth, including the hypothesis about the origin of life from an ice cube, and the theory of the extraterrestrial origin of life, and even the origin of life in places of volcanic activity.

Some of them have scientific confirmation, others have not yet been thoroughly studied. One way or another, of all the existing theories, most of the scientific world supports the theory of Charles Darwin, who suggested that life on Earth originated in a body of water.

According to Darwin's theory, the Earth began to evolve about 4.5 billion years ago, when the first chemical reactions erupted lava, rich in high-energy substances and metals, with water (at that time still sterile), due to which the formation of new molecules began. Thus, for many decades, the ocean acted as a “chemical kitchen” where the main dish was prepared - life.

So far, none of the scientists can answer the question of what the first living organism was - the ancient ancestor of the three main branches of the tree of life: I - eukaryotes (animals, plants, fungi), II - prokaryotes (bacteria), III - archaebacteria (organized like prokaryotes, but with a different lipid structure).

The entire evolution of life on Earth took place in several stages - eras, divided into periods. Thus, in the Archean era (3.5-2.6 billion years ago) - the most ancient era - the first biological breakthrough occurred - the transition from prokaryotes - non-nuclear organisms to nuclear ones.

Gradually absorbing prokaryotic cells and reacting with them, eukaryotes complicated their structure and transformed into complex eukaryotic cells. So aerobic bacteria became mitochondria, and photosynthetic bacteria became chloroplasts. This period marked the beginning of the formation of heterotrophs in water and on land. Soil appeared, and oxygen and carbon dioxide began to accumulate in the atmosphere.

The Proterozoic era (2.6 billion - 570 million years ago) is the next huge stage that reflects the evolution of life on Earth. During this period, sexual reproduction began, which, in turn, led to the emergence of new species of plants and animals. It was during this period that multicellularity emerged, resulting in the appearance of simple coelenterates, worms, sponges and other primitive organisms.

The emergence of multicellular organisms is considered the second biological breakthrough. Throughout the Proterozoic, due to the activity of oceanic plankton, active oxygen accumulated in the atmosphere, resulting in a decrease in the amount of carbon. Thus, the Archean and Proterozoic era (Cryptozoic era) were a period of hidden life on Earth.

The period of the end of the Proterozoic - beginning of the Paleozoic era (600 million years ago) became the third biological breakthrough. At this time, the laying of the skeleton occurred in living organisms. Throughout the Paleozoic era (570-230 million years ago), intensive development of flora and fauna occurred. Fish appeared, animals gradually came out of the water onto land.

As a result of the shrinking of the seas and the rise of the land, the climate changed, and the first forests of horsetails, mosses and giant ferns appeared on the surface of the Earth. This change in the plant world led to the emergence of new species of animals - reptiles, from which mammals and humans later appeared. By the way, people received five fingers on each limb from the first reptile diplovertebron.

The geological era (230-67 million years ago) is divided into periods: Triassic, Jurassic, Cretaceous and is called the era of reptiles, since their mass distribution occurred during this era. At the beginning of the Mesozoic, there was a sharp climate change - drought, because of this, many animals moved to the ocean.

Their limbs atrophied and the first dolphin-like animals appeared - ichthyosaurs and plesiosaurs. In the Triassic, carnivorous and herbivorous dinosaurs appeared. From dinosaurs, the first birds appeared - Archeopteryx (Jurassic period). But real birds, albeit with teeth, appeared already in the Cretaceous period.

During the same period, volcanic activity increased greatly, making the climate more humid. This led to the emergence of new species of dinosaurs: hadrosaurs, ceratopsians, therapods, including tyrannosaurs.

Higher mammals also appeared: marsupials and placentals. Clams, elasmosaurs, and crocodile-like pliosaurs bred in the water. Marine “residents” began to accumulate calcium carbonate, due to which the chalk, limestone and marl deposited on the bottom actively neutralized carbon dioxide in the atmosphere.

At the end of the Mesozoic period there was a mass extinction of flora and fauna. Dinosaurs, pterosaurs and 80% of the entire marine “population” completely disappeared. The cause of this catastrophe is considered to be the fall of an asteroid or comet nucleus, but all these are assumptions... At this stage, the evolution of life on Earth did not stop, but began new era- Cenozoic.

The Cenozoic era, in which we still live (67 million years ago until today), became the era of flowering plants, insects, birds and mammals. It is divided into two periods: tertiary and quaternary.

In the Tertiary period (67 -3 million years ago), tropical and subtropical forests appeared in the plant world, and the first primates appeared in the animal world, which became the ancestors of apes. In the middle of the Tertiary period, all types of animals and plants already existed on the surface of the Earth, and a gradual steppeification of the land began, which led to a reduction in forest areas.

At the same time, some anthropoid monkeys went deep into the forests, while others, on the contrary, descended to the earth and began to actively conquer it. It is this species of monkeys that is the ancestors of people who appeared at the end of the Tertiary period.

In the chervertic period (3 million years ago - our time), the extinction of many animals occurred, in which the hunting instinct developed by ancient people played a large role. Today's way of life (agriculture and cattle breeding) is a consequence of the “Neolithic Revolution”, which occurred about 10 thousand years ago. It was then that people abandoned gathering and hunting.

As we see, the evolution of life on Earth is a very long and rather complex process. But it is to this process that we owe our life and existence.

Approximately 286 million years ago, the warm and wet Carboniferous Period was followed by the Permian. It lasted 41 million years. During this time, the climate on Earth changed, and in a number of areas (Australia, Northern Asia) it became cold. North America and Western Europe became arid and hot places. Conditions changed, plants and animals evolved, adapting to environment. During the Permian period, many new species of reptiles appeared. They developed quickly.

SKULLS AND BONES

In the Permian period, the development of many new reptiles can be traced. How can you find out which group of animals the found bones belong to? One of the main indicators is the skull. The skulls of prehistoric and modern reptiles can be divided into four main groups. These groups are distinguished from each other by the presence or absence of certain depressions or openings in the skull, called apses. They are located behind the eye socket.

The first group is anapsids. Their skulls do not have depressions behind the eyes. These are the very first reptiles, including Hylonomus, today's sea and land turtles. This group also includes fish and amphibians.

The second group is synapsids. On both sides of the skull they have a hole, very low located. Such skulls are found in reptiles similar to mammals, and then in true mammals.

The third group is diapsids. They have two openings on each side of the skull, at the top and bottom. This is what the skulls of the vast majority of extinct and living reptiles look like, including dinosaurs, flying pterosaurs, living lizards, snakes, crocodiles and birds.

The fourth group is the euryapsids or parapsids. Their skulls have one hole on each side, located very high. Some reptiles of the Age of Dinosaurs belonged to this group.

REPTILES WITH CRESTS

A very interesting species of reptile of the Permian period is pelycosaurs. They are also called comb-backed reptiles because they had skin on their backs.
spikes that look like sails.

One of the largest and most ferocious pelycosaurs was Dimetrodon. There are many fossilized remains left of him. It was the first large carnivore over 3 meters long. Dimetrodon lived approximately 260 million years ago on the territory of modern America. Edaphosaurus was similar in shape and size to Dimetrodon, but was herbivorous.

Why do pelycosaurs have such amazing sails on their backs? Scientists believe that with the help of these membranes the animal supported constant temperature bodies.

Most reptiles are cold-blooded. On a cold night, the huge pelycosaurus Dimetrodon became very cold and could not move quickly. In the morning he exposed the membrane to the sun's rays, it quickly warmed up and warmed the whole body. Then Dimetrodon could go hunting for animals that were still clumsy after the cold night. During the day, when the sun burned mercilessly, Dimetrodon stood in the shade and straightened the membrane so that it gave off heat and its body did not overheat. Many dinosaurs had the same membranes.

And yet, this hypothesis about maintaining body temperature with the help of a membrane in no way explains why other pelycosaurs managed and survived without it.

CHANGING EARTH

Ever since the Earth came into being, it has been constantly changing. Over time, huge land masses changed their position on the globe. This phenomenon is called continental drift and continues today.

All this happens due to the fact that the outer rocky shell of the Earth - its crust - does not consist of one piece. It is made up of several giant pieces called tectonic plates. They fit together like a puzzle ball. Their thickness is from 10 to 60 km. The enormous heat and pressure in the Earth's interior causes these plates to move. They swim past each other, find each other, and collide.

At the junction of plates, friction causes shaking of the earth's crust and earthquakes. The collision of plates crushes their edges and forms mountain ranges. In thin places, red-hot lava from the depths of the Earth bursts out through volcanic vents.

Molten rock pours out through cracks on the ocean floor. It cools and solidifies, building up tectonic plates. The plates move apart, and the ocean becomes larger.

SUPERCONTINENT

It's not just tectonic plates that have moved apart over the course of history: sea levels have risen and fallen. The banks changed shape and shifted. This means that in prehistoric times the world was changing all the time.

The position of land masses on the map of the world at that time was sharply different from the modern one. Continental drift, earthquakes, volcanoes, and the formation of mountain ranges greatly influenced the Earth's climate. And climate, in turn, influenced the evolution of plants and animals.

In the early Permian period, all land masses came together and formed one supercontinent - Pangea. In the heart of the continent of Pangea, the climate was dry and hot.

The merging of continents meant that plants and animals could spread across the entire landmass because there were no barriers to them in the form of oceans and seas. But in some places, active volcanoes and mountains became such barriers. This influenced the development of life on Earth.

Amphibians of the PERMian PERIOD

In the Permian period, not only reptiles developed rapidly. Worms, insects, fish and amphibians kept up with them, changing and becoming more and more complex. Plants behaved in the same way: algae appeared in the ocean, aquatic plants appeared in lakes, mosses, ferns and similar plants inhabited the land.

Apart from reptiles, the only large animals on land were amphibians. They became larger and better adapted to hunting other animals. This was Eryops, a massive, wide-bodied and squat animal about 160 cm long. Its fossilized remains (of the Early Permian period, which was 270-260 million years ago) were found in Texas, USA.

Eryops belonged to the group of labyrinthodont amphibians. This is the main species of prehistoric amphibians. They are called so because their teeth have a winding structure, similar to a labyrinth.

IN AMBUSH

Eryops resembles the current crocodile, although its legs are weaker and smaller. He swam on the surface of the water or lay in the mud at the bottom of the lake, as a crocodile does. As soon as the victim gaped, the Eryops flew up, throwing up clouds of silt, and grabbed its prey.

Fossilized Eryops droppings - coprolites - were found near its remains. In it, scientists found the remains of prehistoric fish, for example, the shark of the Permian period - oracanthus. Apparently, Eryops ate fish. He could even get out onto land and walk awkwardly along it. He could not catch up with his victims, but he was quite capable of attacking from an ambush.

LET'S GROW A BIG HEAD!

Ichthyostega also belonged to the group of labyrinthodonts, as did another strange amphibian of the Permian period - diplocaulus. His remains were also found in Texas. The flat body, approximately 1 m long, was equipped with a long tail and small limbs. The strangest thing about diplocaulus is the head.

When scientists discovered his remains, they decided that these were the bones of several different animals. Taking this into account, they were named differently. The strange creatures resembled each other in body shape, but the large specimens had huge, wide bone plates on both sides of their heads, so that the top of their head resembled an arrowhead. The small creatures had much smaller growths on the sides and rounder heads.

RIDDLE SOLVED

As more and more remains were found and piled up, it became clear that they all belonged to diplocaulus. Small individuals with small heads are cubs, and large-headed ones are adults. As it grew, the head of the diplocaulus grew disproportionately quickly, especially the bony lateral processes.

These "horns" could play the same role as the side wings of submarines, helping to support horizontal position body while swimming. Some scientists believe that the outgrowths played the role of a shovel when diplocaulus burrowed into the mud in search of food.

While the Permian period continued, the climate on land became more and more diverse. Some places continued to be hot and humid all year round, while others experienced hot summers and cold winters (almost no precipitation). Amphibians, reptiles and other creatures that ventured to inhabit the earth had to choose: adapt or go extinct.

Many fossils from the Permian period are called the Kleefork Formation, after the Kleefork locality in Texas, USA. These are unusual fossils because they are the remains of animals that did not live in water or in swampy areas. These creatures lived in dry, mountainous places. Such animals include the amphibian cacops and the reptiles casea and varanops. Both reptiles are pelycosaurs, relatives of Dimetrodon.

All three creatures had a long, crocodile-like body and tail. They were smaller in size than their relatives from swamps and lowlands, but their limbs were stronger. They could even raise their torso above the ground and actually walk, unlike Eryops.

WE ADJUSTED AS MUCH AS WE COULD

Creatures like Cacops, Caseea and Varanops show how animals evolved and spread throughout the Earth, even in dry and inhospitable places. Being an amphibian, Cacops needed lakes or swamps to lay its eggs. But puddles and swamps formed only during the rainy season, and then dried up. The offspring had to have time to hatch and grow up. The rest of the time, Kakops learned to do without water; he only went down to the stream to drink.

Some amphibians still live well in dry deserts and savannas. These creatures include the Natterjack toad and the spadefoot toad. Their skin is dry and hard, like sandpaper. It is not at all like the soft, moist skin of amphibians, which spend most of their time in water. The remains of the cacops made it possible to establish that it, too, had tough skin stretched over bony protective protrusions.

GO TO THE MAMMALS!

During the Permian period, many new species of reptiles appeared. One of the species gave rise to dinosaurs and birds. As another species of reptile evolved, the bones of the skull and ears changed and they developed warm-blooded bodies. They became covered with fur, and the animals began to feed their young with milk. These were reptiles similar to mammals.

These were pelycosaurs, for example, Dimetrodon. They gradually became extinct during the middle Permian period, approximately 260 million years ago. New, more developed species of reptiles appeared - therapsids. Their remains are often found in rocks from the middle and late Permian period, especially in South Africa and Russia. Some of the therapsids changed so much that it is difficult to say when they stopped being reptiles and became mammals.

HELMET-HEADED REPTILES

One of the subgroups of therapsids is known as dinocephalians, that is, “terrible-headed”. They were named so because of their thick cranial bones. Some of them were herbivores, others were carnivores.

Moskops is a tall herbivorous reptile with huge, powerful hind legs. The bones of the Moskops skull are so thick that its brain was protected, as it were, by a strong helmet. Perhaps these animals butted heads in the same way that rams and goats do today. Everything is done in a dispute for primacy in the herd, for the right to mate with females and leave offspring. The Moskops must have lived in a herd and also fought to find out who would become the leader.

Another dinocephalus of that era is Estemmenosuchus. His remains are so well preserved that all the details of the structure can be discerned. The skin of this creature has lost the typical scales of reptiles and acquired thin glands that produce sweat and odors in mammals. However, there is no Estemmenosuchus on the skin hairline, characteristic of mammals.

THERAPSID HUNTERS

Therapsid reptiles, similar in appearance to mammals, constitute one of the species - theriodonts. They most closely resembled modern mammals. They were carnivores, and some differed from mammals only in minor details. They lived 250-200 million years ago and then died out when dinosaurs reigned over all land, becoming the largest predators.

Gorgonopsids are also theriodonts. These are large carnivorous reptiles, similar to their pelicodont predecessors, Dimetrodon. A gorgonopsid that lived in Russia in the middle Permian period is Eotitanosuchus. Its length is 2.5 meters, its mouth is strewn with huge sharp teeth, similar to curved sabers. Eotitanosuchus could kill a dinocephalus and obtain enough food for itself for several weeks.

GLOBAL WARMING AND MASS EXTINCTION

Fossilized plants and animals preserved from the Permian period show how the Earth's climate changed during those times. As the supercontinent Pangea moved north, different climate zones emerged around the world. In colder, drier regions appeared a new group plants - coniferous trees. They replaced giant horsetails and tree ferns. Coniferous trees - pines and spruces - survived better in cool, dry climates.

Towards the end of the Permian period the world changed again. Mountain ranges rose, and the movement of continents led to the fact that the huge shallow seas filled with life dried up. The climate became warm and dry. When viewed from the perspective of the vast history of the Earth, these changes occurred very quickly and had an impact big influence to the animal world.

THE GREAT DESTRUCTION OF LIFE

The Permian period witnessed the largest mass extinction event that has ever occurred on Earth. Mass death dinosaurs by the end of the Cretaceous period (65 million years ago) - the most famous case extinction, but other forms of life also died out during the Permian period. Entire classes of plants and animals disappeared.

More than half of the inhabitants of the seas became extinct, including trilobites, huge sea scorpions and animals with the rudiments of lungs, from which amphibians then developed.

The fauna of the land also suffered. Many amphibians and various reptiles, for example, armadillo pareiasaurs, disappeared. At the same time, almost all therapsid reptiles became extinct, including gorgonopsids and dinocephalians.

The Permian period ended approximately 245 million years ago. Its decline meant the end of the first great era of life on Earth. This was the Paleozoic era or "era of ancient life." The next was the Mesozoic era, that is, the “middle life”. It was opened by the Triassic period, in which the first dinosaurs appeared.

The evolution of life on Earth began with the appearance of the first living creature - about 3.7 billion years ago (and according to some sources - 4.1 billion years ago) and continues to this day. The similarities between all organisms indicate the presence of a common ancestor from which all other living things descended.

The entire history of the development of the Earth is divided into eras - long periods of time (from 70 million years to 2 billion years), each of which received its own name.

Archean is the oldest era in the history of the development of the Earth, when life did not yet exist.

Proterozoic - the era of the emergence of primary life (the simplest organisms).

Paleozoic is an era of ancient life in the geological history of the Earth, characterized by the formation of all types of plants and animals.

Mesozoic era average life in the geological history of the Earth, characterized by the development of reptiles, birds and the first mammals.

Cenozoic - the era of new life in the geological history of the Earth, the era of the formation of all modern forms plants and animals. It continues to this day.

Archean era (Archaean) from 3500 to 2500 ± 100 million years ago, duration about 900 million years

Active volcanic activity, anaerobic conditions in a shallow ancient sea, gradual accumulation of oxygen as a result of the activity of photosynthetic prokaryotes. The era of prokaryotes: bacteria and cyanobacteria. Cyanobacteria indicate photosynthesis and the presence of the active pigment chlorophyll. At the border of the Archean and Proterozoic, the first eukaryotes appeared - unicellular algae (green, yellow-green, golden, etc.) and protozoa. Among them are flagellated eukaryotes (Euglenaceae, Volvoxaceae), sarcodes (amoebas, foraminifera, radiolarians), etc. At the border between the Archean and Proterozoic eras, the sexual process and multicellularity appeared.

Proterozoic era (Proterozoic) from 2600 ± 100 to 650-680 ± 20 million years ago, duration about 2000 million years

Paleozoic era (Paleozoic) from 570 ± 20 million years ago to 230 ± 10 million years ago, duration 340 ± 10 million years

The era of active mountain building, which took place in many places on Earth. It is characterized by fairly large finds of fossil organisms. They indicate that during this period aquatic environment Representatives of almost all main types and classes of invertebrate animals lived in salt and fresh water bodies. Later, vertebrates appeared, in addition to birds and mammals. Sharks and descendants of bony fish lived in fresh waters - lungfish and lobe-finned fish, from the latter

In the middle of the era, plants, animals and fungi came to land. The rapid development of higher plants began. Bryophytes appeared. The first forests of giant fern-like plants formed, but at the end of the Paleozoic they died out, forming coal deposits. Air-breathing animals appeared. Reptiles, both herbivores and predators, spread throughout the Earth, and insects appeared.

Mesozoic era (Mesozoic) from 230 ± 10 to 66 ± 3 million years ago, duration about 165 million years

A time of intense mountain building on the periphery of the Pacific, Atlantic and Indian oceans. Often called the Age of Reptiles. They are presented in various forms: floating, flying, land, aquatic and semi-aquatic. Having reached great prosperity, reptiles almost all died out at the end of the Mesozoic. They dominated the seas bony fish and cephalopods. From the beginning of the Mesozoic, the first mammals appeared - oviparous ones, and then marsupials, and from the middle - the first birds. Gymnosperms, especially conifers, became widespread. Angiosperms appear, but are represented only by woody forms. At the end of the Mesozoic, many groups of animals and plants, both terrestrial and aquatic, became extinct.

Cenozoic era (Cenozoic) from 66 ± 3 million years ago to the present

The rise of angiosperms, insects, birds, mammals and the emergence of humans. Already in the middle of the Cenozoic, there were almost all the main groups of representatives of all kingdoms of living nature. Angiosperms developed life forms such as grasses and shrubs. Steppes and meadows appeared. All main types of natural biogeocenoses have been formed. With the advent of man and the development of society, cultural flora and fauna are created, agrocenoses, villages and cities are formed. Nature began to be actively used by man to satisfy his needs. Different Impact man on nature has made significant changes in it. There have been great changes in the species composition of the organic world, in the environment and nature in general.

Lower Tertiary period (Paleogene) - sixth, last period Paleozoic

Beginning 66 ± 3 million years ago

End 25 ± 2 million years ago

Duration about 40 million years

There have been repeated changes in the level of the World Ocean. A warm, uniform climate is established, and mountain formation takes place. Paleogene is the era of the formation of a number of groups of the organic world characteristic of the Cenozoic. From mammals, many orders of mammals appear: rodents, ungulates, bats, proboscideans, secondary aquatic animals - cetaceans and sirenians, true predators. The diversity of birds increased sharply, and most of them still exist today. A number of groups are getting a modern look. Corals, mollusks, and bony fish live in the seas; insects and reptiles (lizards, crocodiles, turtles) live on land. Many classes of invertebrates are characterized by relative poverty in taxonomic composition - the result of significant extinctions at the end of the Mesozoic. In foraminifera, bivalves, sea ​​urchins The composition of families and genera is greatly updated. The plant world is dominated by angiosperms, and elements of modern flora appear. In the middle of the period, heat-loving tropical and subtropical plants move far to the north: laurel trees, palm trees, tropical ferns, etc. At the end of the period, the first apes appear. Due to cooling, the area of ​​distribution of evergreen plants and their communities is decreasing; deciduous plants predominate over a large area.

Upper Tertiary period (Neogene)

Beginning 25 ± 2 million years ago

End about 2 million years ago

Duration about 23 - 25 million years

Cold temperatures led to the appearance of the Antarctic ice sheet. There was an extinction of some ancient groups, especially those associated with wet forests and swampy areas, which is explained by a drier climate and the emergence of forest-steppes and steppes.

Bovids appear, there is a rapid evolution of equines and proboscideans, bears, hyenas, and anteaters are known, pinnipeds and new groups of cetaceans appeared. By the end of the period, real horses, elephants, bulls, and rams appeared.

With the beginning of glaciation on the continents of the Northern Hemisphere and the expansion of glaciation in the Southern Hemisphere, vegetation became more cold-resistant, and the area of ​​steppe associations increased.

The flourishing of ancient apes, among which Dryopithecus, which is the possible ancestor of humans and modern apes, is of particular importance. By the end of the Neogene, Australopithecines arose.

Quaternary period (anthropogenic)

Beginning 1.8 million years ago

Until now

Duration about 1.8 million years

The cooling that began at the end of the Neogene continues; most of the time the climate was colder than today. The last great glaciations in the Northern Hemisphere occur, alternating with interglacial periods. At maximum glaciation, the surface of glaciers in the Southern Hemisphere was 3 times greater than modern ones, and in the Northern Hemisphere - 13 times. During periods of glaciation, the level of the world's oceans decreased, and during interglacial periods it increased by 85 - 120 m. The flora in its systematic composition is close to the modern one, but the location of zonal vegetation was significantly different from the present, especially during the glaciation period. Significant changes in the fauna occurred, mainly at the generic and species level. The mammoth, hairy rhinoceros, reindeer, cave bear and other Arctic forms appeared. Gradually, the modern outlines of the land are finally formed. By the end of the period, modern geographical zones and the appearance of the animal and plant world. The evolution of the genus Homo is taking place. Simultaneously with the formation physical type man, the material culture of the Stone Age developed, ranging from the most primitive to a highly developed culture with its beautiful examples visual arts. Human activity is becoming one of the factors influencing the distribution and extinction of animals and plants. Terrestrial vertebrates originated.

Currently, the plant kingdom is represented by more than 500,000 species, and the animal kingdom is represented by more than 1.2 million species.

During the evolution of the Earth, geological and biological evolution was replaced by a period of social evolution, which brought the largest changes in the Earth's biosphere, in the entire appearance of our planet.

The Holocene (began 11.7 thousand years ago and continues to this day) is a typical interglacial era with a relatively stable climate. The beginning of the Holocene is characterized by the extinction of a large number of animal species, and the middle is characterized by the formation of human civilization and the beginning of its technical development. Changes in the composition of the fauna during this era were relatively small, but animals such as the mammoth or megatherium finally became extinct, and over the last few hundred years some animal species (for example, the dodo, apyornis, Steller's cow) ceased to exist. About 70 years ago, the climate became somewhat warmer (sometimes this is associated with human industrial activity, which supposedly caused the so-called global warming), the North American and Eurasian continental glaciers melted, the Arctic ice sheet disintegrated, many mountain ice sheets ceased to exist, leaving only shrunk shields near the polar caps (Greenland, Antarctica). The development of genetics and genetic engineering began in the 20th century.

The origin of life on Earth is one of the most difficult and at the same time relevant and interest Ask in modern natural science.

The Earth was probably formed 4.5-5 billion years ago from a giant cloud of cosmic dust. the particles of which were compressed into a hot ball. Water vapor was released from it into the atmosphere, and water fell from the atmosphere onto the slowly cooling Earth for millions of years in the form of rain. A prehistoric Ocean formed in the depressions of the earth's surface. The original life arose in it approximately 3.8 billion years ago.

The emergence of life on Earth

How did the planet itself originate and how did the seas appear on it? There is one widely accepted theory about this. According to it, the Earth was formed from clouds of cosmic dust containing all known in nature chemical elements, which were compressed into a ball. Hot water vapor escaped from the surface of this red-hot ball, enveloping it in a continuous cloud cover. The water vapor in the clouds slowly cooled and turned into water, which fell in the form of abundant continuous rains on the still hot, burning Earth. On its surface it again turned into water vapor and returned to the atmosphere. Over millions of years, the Earth gradually lost so much heat that its liquid surface began to harden as it cooled. This is how the earth's crust was formed.

Millions of years passed, and the temperature of the Earth's surface dropped even more. Stormwater stopped evaporating and began to flow into huge puddles. Thus began the influence of water on the earth's surface. And then, due to the drop in temperature, a real flood occurred. The water, which had previously evaporated into the atmosphere and turned into its component, continuously fell to the Earth, with thunder and lightning, powerful showers fell from the clouds.

Little by little, water accumulated in the deepest depressions of the earth's surface, which no longer had time to completely evaporate. There was so much of it that gradually a prehistoric Ocean formed on the planet. Lightning streaked the sky. But no one saw this. There was no life on Earth yet. The continuous rain began to erode the mountains. Water flowed from them in noisy streams and stormy rivers. Over millions of years, water flows have deeply eroded the earth's surface and valleys have appeared in some places. The water content in the atmosphere decreased, and more and more accumulated on the surface of the planet.

The continuous cloud cover became thinner, until one fine day the first ray of the sun touched the Earth. The continuous rain has stopped. Most sushi was covered by the prehistoric Ocean. Water washed away from its upper layers great amount soluble minerals and salts that entered the sea. The water from it continuously evaporated, forming clouds, and the salts settled, and over time, gradual salinization occurred sea ​​water. Apparently, under some conditions that existed in ancient times, substances were formed from which special crystalline forms arose. They grew, like all crystals, and gave rise to new crystals, which added more and more substances to themselves.

Sunlight and possibly very strong electrical discharges served as a source of energy in this process. Perhaps the first inhabitants of the Earth - prokaryotes, organisms without a formed nucleus, similar to modern bacteria - arose from such elements. They were anaerobes, that is, they did not use free oxygen for breathing, which did not yet exist in the atmosphere. The source of food for them was organic compounds that arose on the still lifeless Earth as a result of exposure to ultraviolet radiation The sun, thunderstorms and heat generated by volcanic eruptions.

Life then existed in a thin bacterial film at the bottom of reservoirs and in damp places. This era of the development of life is called Archean. From bacteria, and perhaps in a completely independent way, tiny single-celled organisms arose - the most ancient protozoa.

What did the primitive Earth look like?

Let's fast forward to 4 billion years ago. The atmosphere does not contain free oxygen; it is found only in oxides. Almost no sounds except the whistle of the wind, the hiss of water erupting with lava and the impacts of meteorites on the surface of the Earth. No plants, no animals, no bacteria. Maybe this is what the Earth looked like when life appeared on it? Although this problem has long been of concern to many researchers, their opinions on this matter vary greatly. Rocks could indicate conditions on Earth at that time, but they were destroyed long ago as a result of geological processes and movements of the earth's crust.

Theories of the origin of life on Earth

In this article we will briefly talk about several hypotheses for the origin of life, reflecting modern scientific ideas. According to Stanley Miller, a well-known expert in the field of the origin of life, we can talk about the origin of life and the beginning of its evolution from the moment when organic molecules self-organized into structures that were able to reproduce themselves. But this raises other questions: how did these molecules arise; why they could reproduce themselves and assemble into those structures that gave rise to living organisms; what conditions are needed for this?

There are several theories about the origin of life on Earth. For example, one of the long-standing hypotheses says that it was brought to Earth from space, but there is no conclusive evidence of this. In addition, the life that we know is surprisingly adapted to exist precisely in terrestrial conditions, so if it arose outside the Earth, it would have been on the planet earth type. Most modern scientists believe that life originated on Earth, in its seas.

Biogenesis theory

In the development of doctrines about the origin of life, the theory of biogenesis - the origin of living things only from living things - occupies a significant place. But many consider it untenable, since it fundamentally contrasts the living with the inanimate and affirms the idea of ​​​​the eternity of life, rejected by science. Abiogenesis - the idea of ​​the origin of living things from non-living things - the original hypothesis modern theory origin of life. In 1924, the famous biochemist A.I. Oparin suggested that with powerful electrical discharges in the earth’s atmosphere, which 4-4.5 billion years ago consisted of ammonia, methane, carbon dioxide and water vapor, the simplest organic compounds could arise, necessary for the emergence of life. Academician Oparin's prediction came true. In 1955, American researcher S. Miller, passing electrical charges through a mixture of gases and vapors, obtained the simplest fatty acids, urea, acetic and formic acids and several amino acids. Thus, in the middle of the 20th century, the abiogenic synthesis of protein-like and other organic matter in conditions reproducing the conditions of the primitive Earth.

Panspermia theory

The theory of panspermia is the possibility of transferring organic compounds and spores of microorganisms from one cosmic body to another. But it does not answer the question at all: how did life originate in the Universe? There is a need to substantiate the emergence of life at that point in the Universe, the age of which, according to the theory big bang, is limited to 12-14 billion years. Before this time there were not even elementary particles. And if there are no nuclei and electrons, there is no chemical substances. Then, within a few minutes, protons, neutrons, electrons appeared, and matter entered the path of evolution.

To substantiate this theory, multiple sightings of UFOs, rock paintings of objects resembling rockets and “astronauts,” and reports of alleged encounters with aliens are used. When studying the materials of meteorites and comets, many “precursors of life” were discovered in them - substances such as cyanogens, hydrocyanic acid and organic compounds, which may have played the role of “seeds” that fell on the bare Earth.

The supporters of this hypothesis were the laureates Nobel Prize F. Crick, L. Orgel. F. Crick was based on two indirect evidence: the universality of the genetic code: the need for the normal metabolism of all living beings of molybdenum, which is now extremely rare on the planet.

The origin of life on Earth is impossible without meteorites and comets

A researcher from Texas Tech University, after analyzing a huge amount of collected information, put forward a theory about how life could form on Earth. The scientist is sure that the appearance early forms simplest life on our planet would have been impossible without the participation of comets and meteorites that fell on it. The researcher shared his work at the 125th annual meeting of the Geological Society of America, held on October 31 in Denver, Colorado.

The author of the work, a professor of geoscience at Texas Tech University (TTU) and curator of the university's museum of paleontology, Sankar Chatterjee, said that he came to this conclusion after analyzing information about the early geological history of our planet and comparing this data with various theories of chemical evolution.

The expert believes that this approach makes it possible to explain one of the most hidden and incompletely studied periods in the history of our planet. According to many geologists, the bulk of space “bombardments”, in which comets and meteorites took part, occurred about 4 billion years ago. Chatterjee believes that the most early life on Earth formed in craters left by the fall of meteorites and comets. And most likely this happened during the “Late Heavy Bombardment” period (3.8-4.1 billion years ago), when the collision of small space objects with our planet increased sharply. At that time, there were several thousand cases of comet falls. Interestingly, this theory is indirectly supported by the Nice Model. According to it, the real number of comets and meteorites that should have fallen to the Earth at that time corresponds to the real number of craters on the Moon, which in turn was a kind of shield for our planet and did not allow the endless bombardment to destroy it.

Some scientists suggest that the result of this bombardment is the colonization of life in the Earth's oceans. However, several studies on this topic indicate that our planet has more water reserves than it should. And this excess is attributed to comets that came to us from the Oort Cloud, which is supposedly located one light year away from us.

Chatterjee points out that the craters created by these collisions were filled with melted water from the comets themselves, as well as the necessary chemical building blocks needed to form simple organisms. At the same time, the scientist believes that those places where life did not appear even after such a bombardment simply turned out to be unsuitable for this.

“When the Earth was formed about 4.5 billion years ago, it was completely unsuitable for living organisms to appear on it. It was a real boiling cauldron of volcanoes, poisonous hot gas and meteorites constantly falling on it,” writes the online magazine AstroBiology, citing the scientist.

“And after one billion years, it became a quiet and peaceful planet, rich in huge reserves of water, inhabited by various representatives of microbial life - the ancestors of all living things.”

Life on Earth could have arisen thanks to clay

A group of scientists led by Dan Luo from Cornell University came up with a hypothesis that ordinary clay could serve as a concentrator for ancient biomolecules.

Initially, the researchers were not concerned with the problem of the origin of life - they were looking for a way to increase the efficiency of cell-free protein synthesis systems. Instead of allowing the DNA and its supporting proteins to float freely in the reaction mixture, the scientists tried to force them into hydrogel particles. This hydrogel, like a sponge, absorbed the reaction mixture, sorbed the necessary molecules, and as a result, all the necessary components were locked in a small volume - similar to what happens in a cell.

The study authors then tried to use clay as an inexpensive hydrogel substitute. Clay particles turned out to be similar to hydrogel particles, becoming a kind of microreactors for interacting biomolecules.

Having received such results, scientists could not help but recall the problem of the origin of life. Clay particles, with their ability to sorb biomolecules, could actually serve as the very first bioreactors for the very first biomolecules, before they yet acquired membranes. This hypothesis is also supported by the fact that the leaching of silicates and other minerals from rocks to form clay began, according to geological estimates, just before, according to biologists, the oldest biomolecules began to unite into protocells.

In water, or more precisely in a solution, little could happen, because the processes in a solution are absolutely chaotic, and all compounds are very unstable. Modern science considers clay - more precisely, the surface of particles of clay minerals - as a matrix on which primary polymers could form. But this is also only one of many hypotheses, each of which has its own strong and weak sides. But to simulate the origin of life on a full scale, you really need to be God. Although in the West today articles with the titles “Cell Construction” or “Cell Modeling” are already appearing. For example, one of the last Nobel laureates, James Szostak, is now actively attempting to create effective cell models that multiply on their own, reproducing their own kind.