Each of us sometimes worries about such questions that are difficult to find answers. These include understanding the meaning of one's existence, the structure of the world, and much more. We believe that everyone once thought about the development of life on Earth. The eras that we know are very different from each other. In this article, we will analyze in detail, and how exactly its evolution took place.

catarchean

Katarchaeus - when the earth was lifeless. There were volcanic eruptions everywhere, ultraviolet radiation and no oxygen. The evolution of life on Earth began its countdown precisely from this period. Due to the interaction of chemicals that have enveloped the earth, properties characteristic of life on Earth begin to form. However, there is another opinion. Some historians believe that the Earth has never been empty. In their opinion, the planet exists as long as life on it.

The katarchean era lasted from 5 to 3 billion years ago. Studies have shown that during this period the planet did not have a core and the earth's crust. An interesting fact is that at that time the day lasted only 6 hours.

archaeus

The next era after the Catarchean is the Archean (3.5-2.6 billion years BC). It is divided into four periods:

• neoarchean;
• mesoarchean;
• paleoarchaean;
• eoarchean.

It was during the Archean that the first simple microorganisms arose. Few people know, but the deposits of sulfur and iron that we mine today appeared during this period. Archaeologists have found the remains of filamentous algae, the age of which allows them to be attributed to the Archean period. At this time, the evolution of life on Earth continued. heterotrophic organisms appear. Soil is formed.

Proterozoic

The Proterozoic is one of the longest periods of the Earth's development. It is divided into the following steps:

• mesoproterozoic;
• neoproterozoic.

This period is characterized by the appearance of the ozone layer. Also, it was at this time, according to historians, that the volume of the world ocean was fully formed. The Paleoproterozoic era included the Siderian period. It was in it that the formation of anaerobic algae occurred.

Scientists note that it was in the Proterozoic that global glaciation occurred. It lasted for 300 million years. A similar situation is characterized by the ice age, which was much later. During the Proterozoic, sponges and fungi appeared among them. It was during this period that deposits of ore and gold were formed. The Neoproterozoic era is characterized by the formation of new continents. Scientists note that all the flora and fauna that existed during this period is not the ancestor of modern animals and plants.

Paleozoic

Scientists have been studying the geological eras of the Earth and the development of the organic world for a long time. In their opinion, the Paleozoic is one of the most significant periods for our modern life. It lasted about 200 million years and is divided into 6 time periods. It was during this era of the development of the Earth that land plants began to form. It is worth noting that during the Paleozoic period, animals came to land.

The Paleozoic era was studied by many famous scientists. Among them are A. Sedgwick and E. D. Phillips. It was they who divided the era into certain periods.

Paleozoic climate

Many scientists have done research to find out the Era, as we said earlier, could last long enough. It is for this reason that during one chronology on a certain part of the Earth at different times there can be an absolutely opposite climate. So it was in the Paleozoic. At the beginning of the era, the climate was milder and warmer. There was no zoning as such. The percentage of oxygen constantly increased. The water temperature was between 20 degrees Celsius. Over time, zonation began to appear. The climate became hotter and more humid.

By the end of the Paleozoic, as a result of the formation of vegetation, active photosynthesis began. A more pronounced zoning appeared. Climatic zones formed. This stage has become one of the most important for the development of life on Earth. The Paleozoic era gave impetus to the enrichment of the planet with flora and fauna.

Flora and fauna of the Paleozoic era

At the beginning of the Paleosian period, life was concentrated in water bodies. In the middle of the era, when the amount of oxygen reached a high level, land development began. Its very first inhabitants were plants, which first performed their vital activity in shallow water, and then moved to the shore. The first representatives of the flora that mastered the land are psilophytes. It is worth noting that they did not have roots. The process of formation of gymnosperms is also referred to the Paleozoic era. Tree-like plants also appeared. In connection with the appearance of flora on earth, animals gradually began to appear. Scientists suggest that herbivorous forms were the first to arise. The process of development of life on Earth lasted for quite a long time. Era and living organisms are constantly changing. The first representatives of the fauna are invertebrates and spiders. Over time, insects with wings, ticks, mollusks, dinosaurs, reptiles appeared. In the late period of the Paleozoic, significant climatic changes occurred. This led to the extinction of some animal species. According to preliminary estimates, about 96% of the inhabitants of the water and 70% of the land died.

Minerals of the Paleozoic era

It is with the Paleozoic period that the formation of many minerals is associated. Rock salt deposits began to form. It is also worth emphasizing that some oil basins originate precisely from the beginning of the formation of coal strata, which account for 30% of the total. Also, the formation of mercury is associated with the Paleozoic period.

Mesozoic

The next after the Paleozoic was the Mesozoic. It lasted about 186 million years. The geological history of the Earth began much earlier. However, it was the Mesozoic that became the era of activity, both climatic and evolutionary. The main boundaries of the continents were formed. Mountain building has begun. There was a division of Eurasia and America. It is believed that it was in the climate that was the warmest. However, at the end of the era, the ice age began, which significantly changed the flora and fauna of the earth. Natural selection has taken place.

Flora and fauna in the Mesozoic era

The Mesozoic era is characterized by the extinction of ferns. Gymnosperms and conifers predominate. Angiosperms are formed. It was in the Mesozoic period that the fauna flourished. The most developed are reptiles. In this period, there were a large number of their subspecies. Flying reptiles appear. Their growth continues. By the end, some representatives weigh about 50 kilograms.

In the Mesozoic, the development of flowering plants gradually begins. By the end of the period, a cold snap sets in. The number of subspecies of near-aquatic plants is decreasing. Gradually, invertebrates also die out. It is for this reason that birds and mammals appear.

According to scientists, birds originated from dinosaurs. They associate the emergence of mammals with one of the subclasses of reptiles.

Cenozoic

Cenozoic is exactly the era in which we live today. It began about 66 million years ago. At the beginning of the era, the division of the continents was still taking place. Each of them was dominated by its own flora, fauna and climate.

Cenozoic is distinguished by a large number of insects, flying and marine animals. Mammals and angiosperms predominate. It was at this time that all living organisms evolve strongly and are distinguished by a large number of subspecies. Grains appear. The most important transformation is the emergence of Homo sapiens.

Human evolution. Initial stages of development

The exact age of the planet cannot be determined. Scientists have been arguing about this topic for a long time. Some believe that the age of the Earth is 6,000 thousand years, others that it is more than 6 million. Guess we'll never know the truth. The most important achievement of the Cenozoic era is the appearance of Homo sapiens. Let's take a closer look at exactly how this happened.

There are a large number of opinions regarding the formation of mankind. Scientists have repeatedly compared a wide variety of sets of DNA. They came to the conclusion that monkeys have the most similar organism to humans. It is impossible to prove this theory to the end. Some scientists argue that the human and pig bodies are also quite similar.

Human evolution is visible to the naked eye. At first, biological factors were important for the population, and today social factors are important. Neanderthal, Cro-Magnon, Australopithecus and others - all of which our ancestors went through.

Parapithecus is the first stage in the development of modern man. At this stage, our ancestors existed - monkeys, namely chimpanzees, gorillas and orangutans.

Australopithecus was the next stage of development. The first found remains were in Africa. According to preliminary data, their age is about 3 million years. Scientists examined the find and came to the conclusion that australopithecines are quite similar to modern humans. The growth of representatives was quite small, about 130 centimeters. The mass of Australopithecus was 25-40 kilograms. The guns, most likely, they did not use, since they were never found.

A skilled man was similar to Australopithecus, but, unlike them, he used a primitive tool. His hands and knuckles were more developed. It is believed that a skilled person is our direct ancestor.

Pithecanthropus

The next stage of evolution was Pithecanthropus - Homo erectus. Its first remains were found on the island of Java. According to scientists, pithecanthropes lived on the Earth about a million years ago. Later, the remains of Homo erectus were found in all corners of the planet. Based on this, we can conclude that Pithecanthropes inhabited all continents. The body of a erect human was not much different from the modern one. However, there were minor differences. Pithecanthropus had a low forehead and well-defined brow ridges. Scientists have found that an upright person led an active lifestyle. Pithecanthropes hunted and made simple tools. They lived in groups. So it was easier for Pithecanthropes to hunt and defend themselves from the enemy. Finds in China allow us to conclude that they also knew how to use fire. Pithecanthropes developed abstract thinking and speech.

Neanderthal

Neanderthals lived about 350 thousand years ago. Found about 100 remains of their life. The Neanderthal skull was domed. Their height was about 170 centimeters. They had a fairly large physique, well-developed muscles and good physical strength. They had to live in the Ice Age. It is thanks to this that Neanderthals learned to sew clothes from leather and constantly keep fire. There is an opinion that Neanderthals lived only on the territory of Eurasia. It is also worth noting that they carefully processed the stone for the future tool. The Neanderthals often used wood. From it they created a tool of labor and elements for dwellings. However, it is worth noting that they were quite primitive.

Cro-Magnon

Cro-Magnons were tall, which was about 180 centimeters. They had all the signs of modern man. Over the past 40 thousand years, their appearance has not changed at all. After analyzing the remains of a person, scientists concluded that the average age of the Cro-Magnons was about 30-50 years. It is worth noting that they created more complex types of weapons. Among them are knives and harpoons. The Cro-Magnons fished, and therefore, in addition to the standard set of weapons, they also created new ones for comfortable fishing. Among them are needles and much more. From this we can conclude that the Cro-Magnons had a well-developed brain and logic.

A reasonable man built his dwelling out of stone or dug it out of the ground. The nomadic population created temporary huts for greater convenience. It is also worth noting that the Cro-Magnons tamed the wolf, turning it over time into a watchdog.

Cro-Magnons and art

Few people know that it was the Cro-Magnons who formed the concept that we now know as the concept of creativity. On the walls of a large number of caves, rock paintings made by the Cro-Magnons were found. It is worth emphasizing that the Cro-Magnons always left their drawings in hard-to-reach places. Perhaps they performed some kind of magical role.

The Cro-Magnon people had a variety of drawing techniques. Some clearly traced the images, while others scratched them. Cro-Magnons used colored paints. Predominantly red, yellow, brown and black. Over time, they even began to carve human figures. You can easily find all the exhibits found in almost any archaeological museum. Scientists note that the Cro-Magnons were quite developed and educated. They liked to wear jewelry made from the bones of the animals they had killed.

There is quite an interesting opinion. Previously, it was believed that the Cro-Magnons ousted the Neanderthals in an unequal struggle. Scientists today think otherwise. They believe that for a certain amount of time, Neanderthals and Cro-Magnons lived side by side, but the weaker ones died from a sharp cold snap.

Summing up

The geological history of the Earth began many millions of years ago. Each era has contributed to our modern life. We often do not think about how our planet has evolved. Studying the information about how our Earth was formed, it is impossible to stop. The history of the evolution of the planet can bewitch everyone. We strongly recommend that we take care of our Earth, if only so that after millions of years there will be someone to study the history of our existence.

At first there was nothing. In the boundless outer space, there was only a giant cloud of dust and gases. It can be assumed that from time to time spaceships with representatives of the universal mind rushed through this substance at great speed. The humanoids boredly looked out of the windows and did not even remotely guess that in a few billion years intelligence and life would arise in these places.

The gas and dust cloud eventually transformed into the solar system. And after the luminary appeared, the planets appeared. One of them was our native Earth. It happened 4.5 billion years ago. It is from those distant times that the age of the blue planet is counted, thanks to which we exist in this world.

Stages of the Earth's development

The entire history of the Earth is divided into two huge time periods. The first stage is characterized by the absence of complex living organisms. There were only single-celled bacteria that settled on our planet about 3.5 billion years ago. The second stage began about 540 million years ago. This is the time when living multicellular organisms settled on the Earth. This refers to both plants and animals. Moreover, both seas and land became their habitat. The second period continues to this day, and its crown is man.

Such huge time steps are called eons. Each eon has its own eonoteme. The latter represents a certain stage in the geological development of the planet, which is fundamentally different from other stages in the lithosphere, hydrosphere, atmosphere, and biosphere. That is, each eonoteme is strictly specific and not similar to others.

There are 4 aeons in total. Each of them, in turn, is divided into eras of the Earth, and those are divided into periods. This shows that there is a rigid gradation of large time intervals, and the geological development of the planet is taken as the basis.

catarchean

The most ancient eon is called Katarchaeus. It began 4.6 billion years ago and ended 4 billion years ago. Thus, its duration was 600 million years. Time is very ancient, so it was not divided into eras or periods. At the time of the Katarchean, there was neither the earth's crust nor the core. The planet was a cold cosmic body. The temperature in its bowels corresponded to the melting point of the substance. From above, the surface was covered with regolith, like the lunar surface in our time. The relief was almost flat due to constant powerful earthquakes. Naturally, there was no atmosphere and oxygen.

archaeus

The second aeon is called Archaea. It began 4 billion years ago and ended 2.5 billion years ago. Thus, it lasted 1.5 billion years. It is divided into 4 eras: Eoarchean, Paleoarchean, Mesoarchean and Neoarchean.

Eoarchean(4-3.6 billion years) lasted 400 million years. This is the period of formation of the earth's crust. A huge number of meteorites fell on the planet. This is the so-called Late Heavy Bombardment. It was at that time that the formation of the hydrosphere began. Water appeared on Earth. In large quantities, comets could bring it. But the oceans were still far away. There were separate reservoirs, and the temperature in them reached 90 ° Celsius. The atmosphere was characterized by a high content of carbon dioxide and a low content of nitrogen. There was no oxygen. At the end of the era, the first supercontinent of Vaalbar began to form.

paleoarchaean(3.6-3.2 billion years) lasted 400 million years. In this era, the formation of the solid core of the Earth was completed. There was a strong magnetic field. His tension was half the current. Consequently, the surface of the planet received protection from the solar wind. This period also includes primitive life forms in the form of bacteria. Their remains, which are 3.46 billion years old, have been found in Australia. Accordingly, the oxygen content in the atmosphere began to increase, due to the activity of living organisms. The formation of Vaalbar continued.

Mesoarchean(3.2-2.8 billion years) lasted 400 million years. Most notable was the existence of cyanobacteria. They are capable of photosynthesis and release oxygen. The formation of a supercontinent has been completed. By the end of the era, it had split. There was also a fall of a huge asteroid. A crater from it still exists on the territory of Greenland.

neoarchean(2.8-2.5 billion years) lasted 300 million years. This is the time of formation of the real earth's crust - tectogenesis. Bacteria continued to grow. Traces of their life are found in stromatolites, whose age is estimated at 2.7 billion years. These lime deposits were formed by huge colonies of bacteria. They are found in Australia and South Africa. Photosynthesis continued to improve.

With the end of the Archean, the eras of the Earth were continued in the Proterozoic eon. This is a period of 2.5 billion years - 540 million years ago. It is the longest of all eons on the planet.

Proterozoic

The Proterozoic is divided into 3 eras. The first is called Paleoproterozoic(2.5-1.6 billion years). It lasted 900 million years. This huge time interval is divided into 4 periods: siderium (2.5-2.3 billion years), riasium (2.3-2.05 billion years), orosirium (2.05-1.8 billion years) , statery (1.8-1.6 billion years).

siderius remarkable in the first place oxygen catastrophe. It happened 2.4 billion years ago. It is characterized by a radical change in the Earth's atmosphere. It contained a large amount of free oxygen. Prior to this, the atmosphere was dominated by carbon dioxide, hydrogen sulfide, methane and ammonia. But as a result of photosynthesis and the extinction of volcanic activity at the bottom of the oceans, oxygen filled the entire atmosphere.

Oxygen photosynthesis is characteristic of cyanobacteria that bred on Earth 2.7 billion years ago. Prior to this, archaebacteria dominated. They do not produce oxygen during photosynthesis. In addition, at first oxygen was spent on the oxidation of rocks. In large quantities, it accumulated only in biocenoses or bacterial mats.

In the end, the moment came when the surface of the planet was oxidized. And the cyanobacteria continued to release oxygen. And it began to accumulate in the atmosphere. The process has accelerated due to the fact that the oceans also stopped absorbing this gas.

As a result, anaerobic organisms died, and they were replaced by aerobic ones, that is, those in which energy synthesis was carried out through free molecular oxygen. The planet was enveloped in the ozone layer and the greenhouse effect decreased. Accordingly, the boundaries of the biosphere expanded, and sedimentary and metamorphic rocks turned out to be completely oxidized.

All these metamorphoses led to Huron glaciation, which lasted 300 million years. It began in the siderium, and ended at the end of the riasian 2 billion years ago. The next Orosirium period notable for intensive mountain building processes. At this time, 2 huge asteroids fell on the planet. The crater from one is called Vredefort and is located in South Africa. Its diameter reaches 300 km. Second crater Sudbury is located in Canada. Its diameter is 250 km.

Last statheric period notable for the formation of the supercontinent Columbia. It included almost all the continental blocks of the planet. There was a supercontinent 1.8-1.5 billion years ago. At the same time, cells were formed that contained nuclei. That is eukaryotic cells. This was a very important stage in evolution.

The second era of the Proterozoic is called mesoproterozoic(1.6-1 billion years). Its duration was 600 million years. It is divided into 3 periods: potassium (1.6-1.4 billion years), exatium (1.4-1.2 billion years), stenium (1.2-1 billion years).

At the time of the kalimium, the supercontinent Columbia collapsed. And during the time of exatia, red multicellular algae appeared. This is indicated by a fossil find on the Canadian island of Somerset. Its age is 1.2 billion years. A new supercontinent, Rodinia, formed in the walls. It arose 1.1 billion years ago, and broke up 750 million years ago. Thus, by the end of the Mesoproterozoic, there was 1 supercontinent and 1 ocean on Earth, which was called Mirovia.

The last era of the Proterozoic is called neoproterozoic(1 billion-540 million years). It includes 3 periods: Tonian (1 billion-850 million years), Cryogeny (850-635 million years), Ediacaran (635-540 million years).

During the time of Toni, the disintegration of the supercontinent Rodinia began. This process ended in cryogeny, and the Pannotia supercontinent began to form from 8 separate pieces of land formed. Cryogeny is also characterized by complete glaciation of the planet (Snowball Earth). The ice reached the equator, and after they receded, the process of evolution of multicellular organisms sharply accelerated. The last period of the Neoproterozoic Ediacaran is notable for the appearance of soft-bodied creatures. These multicellular animals are called vendobionts. They were branching tubular structures. This ecosystem is considered the oldest.

Life on Earth originated in the ocean

Phanerozoic

Approximately 540 million years ago, the time of the 4th and last eon, the Phanerozoic, began. There are 3 very important eras of the Earth here. The first is called Paleozoic(540-252 million years). It lasted 288 million years. It is divided into 6 periods: Cambrian (540-480 million years), Ordovician (485-443 million years), Silurian (443-419 million years), Devonian (419-350 million years), Carboniferous (359-299 Ma) and Permian (299-252 Ma).

Cambrian considered the lifetime of trilobites. These are marine animals that look like crustaceans. Together with them, jellyfish, sponges and worms lived in the seas. This abundance of living beings is called Cambrian explosion. That is, there was nothing like this before, and suddenly it suddenly appeared. Most likely, it was in the Cambrian that mineral skeletons began to emerge. Previously, the living world had soft bodies. They, of course, did not survive. Therefore, complex multicellular organisms of more ancient eras cannot be detected.

The Paleozoic is notable for the rapid spread of organisms with hard skeletons. From vertebrates, fish, reptiles and amphibians appeared. In the plant world, algae predominated at first. During Silurian plants began to colonize the land. At the beginning Devonian swampy shores are overgrown with primitive representatives of the flora. These were psilophytes and pteridophytes. Plants reproduced by spores carried by the wind. Plant shoots developed on tuberous or creeping rhizomes.

Plants began to develop land in the Silurian period

There were scorpions, spiders. The real giant was the Meganevra dragonfly. Its wingspan reached 75 cm. Acanthodes are considered the oldest bony fish. They lived during the Silurian period. Their bodies were covered with dense diamond-shaped scales. IN carbon, which is also called the Carboniferous period, the most diverse vegetation flourished on the shores of the lagoons and in countless swamps. It was its remains that served as the basis for the formation of coal.

This time is also characterized by the beginning of the formation of the supercontinent Pangea. It was fully formed in the Permian period. And it broke up 200 million years ago into 2 continents. These are the northern continent of Laurasia and the southern continent of Gondwana. Subsequently, Laurasia split, and Eurasia and North America were formed. And South America, Africa, Australia and Antarctica arose from Gondwana.

On the Permian there were frequent climate changes. Dry times gave way to wet ones. At this time, lush vegetation appeared on the banks. Typical plants were cordaites, calamites, tree and seed ferns. Mesosaurus lizards appeared in the water. Their length reached 70 cm. But by the end of the Permian period, early reptiles died out and gave way to more developed vertebrates. Thus, in the Paleozoic, life reliably and densely settled on the blue planet.

Of particular interest to scientists are the following eras of the Earth. 252 million years ago mesozoic. It lasted 186 million years and ended 66 million years ago. It consisted of 3 periods: Triassic (252-201 million years), Jurassic (201-145 million years), Cretaceous (145-66 million years).

The border between the Permian and the Triassic period is characterized by the mass extinction of animals. 96% of marine species and 70% of terrestrial vertebrates died. A very strong blow was dealt to the biosphere, and it took a very long time to recover. And it all ended with the appearance of dinosaurs, pterosaurs and ichthyosaurs. These sea and land animals were of enormous size.

But the main tectonic event of those years - the collapse of Pangea. A single supercontinent, as already mentioned, was divided into 2 continents, and then broke up into those continents that we know now. The Indian subcontinent also broke away. Subsequently, it connected with the Asian plate, but the collision was so violent that the Himalayas were created.

Such nature was in the early Cretaceous period

The Mesozoic is notable for being considered the warmest period of the Phanerozoic eon.. This is the time of global warming. It began in the Triassic and ended at the end of the Cretaceous. For 180 million years, even in the Arctic there were no stable pack glaciers. Heat spread evenly throughout the planet. At the equator, the average annual temperature corresponded to 25-30 ° Celsius. The polar regions were characterized by a moderately cool climate. In the first half of the Mesozoic, the climate was dry, while the second half was characterized by humid. It was at this time that the equatorial climatic zone was formed.

In the animal world, mammals arose from a subclass of reptiles. This was due to the improvement of the nervous system and brain. The limbs moved from the sides under the body, the reproductive organs became more perfect. They ensured the development of the embryo in the mother's body, followed by feeding it with milk. A woolen cover appeared, blood circulation and metabolism improved. The first mammals appeared in the Triassic, but they could not compete with dinosaurs. Therefore, for more than 100 million years, they occupied a dominant position in the ecosystem.

The last era is Cenozoic(beginning 66 million years ago). This is the current geological period. That is, we all live in the Cenozoic. It is divided into 3 periods: the Paleogene (66-23 million years), the Neogene (23-2.6 million years) and the modern anthropogen or Quaternary period, which began 2.6 million years ago.

There are 2 major events in the Cenozoic. The mass extinction of dinosaurs 65 million years ago and the general cooling on the planet. The death of animals is associated with the fall of a huge asteroid with a high content of iridium. The diameter of the cosmic body reached 10 km. This resulted in the formation of a crater. Chicxulub with a diameter of 180 km. It is located on the Yucatan Peninsula in Central America.

Earth's surface 65 million years ago

After the fall, there was an explosion of great force. Dust rose into the atmosphere and covered the planet from the sun's rays. The average temperature dropped by 15°. Dust hung in the air for a whole year, which led to a sharp cooling. And since the Earth was inhabited by large heat-loving animals, they died out. Only small representatives of the fauna remained. It was they who became the ancestors of the modern animal world. This theory is based on iridium. The age of its layer in geological deposits corresponds exactly to 65 million years.

During the Cenozoic, the continents diverged. Each of them formed its own unique flora and fauna. The diversity of marine, flying and land animals has increased significantly in comparison with the Paleozoic. They have become much more advanced, and mammals have taken the dominant position on the planet. In the plant world, higher angiosperms appeared. This is the presence of a flower and an ovule. There were also cereal crops.

The most important thing in the last era is anthropogen or Quaternary, which began 2.6 million years ago. It consists of 2 epochs: the Pleistocene (2.6 million years - 11.7 thousand years) and the Holocene (11.7 thousand years - our time). During the Pleistocene era mammoths, cave lions and bears, marsupial lions, saber-toothed cats and many other animal species that became extinct at the end of the era lived on Earth. 300 thousand years ago, a man appeared on the blue planet. It is believed that the first Cro-Magnons chose for themselves the eastern regions of Africa. At the same time, Neanderthals lived on the Iberian Peninsula.

Notable for the Pleistocene and Ice Ages. For a whole 2 million years, very cold and warm periods of time alternated on Earth. Over the past 800 thousand years, there have been 8 ice ages with an average duration of 40 thousand years. In cold times, glaciers advanced on the continents, and receded in interglacials. At the same time, the level of the World Ocean was rising. About 12 thousand years ago, already in the Holocene, another ice age ended. The climate became warm and humid. Thanks to this, humanity has settled all over the planet.

The Holocene is an interglacial. It has been going on for 12 thousand years. Human civilization has been developing for the last 7 thousand years. The world has changed in many ways. Significant transformations, thanks to the activities of people, have undergone flora and fauna. Today, many animal species are on the verge of extinction. Man has long considered himself the ruler of the world, but the eras of the Earth have not disappeared. Time continues its steady course, and the blue planet conscientiously revolves around the Sun. In a word, life goes on, but what will happen next - the future will show.

The article was written by Vitaly Shipunov

The emergence of the Earth and the early stages of its formation

One of the important tasks of modern natural science in the field of Earth sciences is the restoration of the history of its development. According to modern cosmogonic concepts, the Earth was formed from the gas and dust matter scattered in the protosolar system. One of the most probable variants of the origin of the Earth is as follows. Initially, the Sun and a flattened rotating circumsolar nebula were formed from an interstellar gas and dust cloud under the influence of, for example, the explosion of a nearby supernova. Next, the evolution of the Sun and the circumsolar nebula took place with the transmission of the moment of momentum from the Sun to the planets by electromagnetic or turbulent-convective methods. Subsequently, the "dusty plasma" condensed into rings around the Sun, and the material of the rings formed the so-called planetesimals, which condensed to planets. After that, a similar process was repeated around the planets, which led to the formation of satellites. This process is believed to have taken about 100 million years.

It is assumed that further, as a result of the differentiation of the Earth's substance under the influence of its gravitational field and radioactive heating, different in chemical composition, state of aggregation and physical properties of the shell - the Earth's geosphere - arose and developed. The heavier material formed a core, probably composed of iron mixed with nickel and sulfur. Somewhat lighter elements remained in the mantle. According to one of the hypotheses, the mantle is composed of simple oxides of aluminum, iron, titanium, silicon, etc. The composition of the earth's crust has already been discussed in sufficient detail in § 8.2. It is composed of lighter silicates. Even lighter gases and moisture formed the primary atmosphere.

As already mentioned, it is assumed that the Earth was born from a cluster of cold solid particles that fell out of a gas and dust nebula and stuck together under the influence of mutual attraction. As the planet grew, it warmed up due to the collision of these particles, which reached several hundred kilometers, like modern asteroids, and the release of heat not only by naturally radioactive elements now known to us in the crust, but also by more than 10 radioactive isotopes Al, Be, which have since died out. Cl, etc. As a result, complete (in the core) or partial (in the mantle) melting of the substance could occur. In the initial period of its existence, up to about 3.8 billion years, the Earth and other planets of the terrestrial group, as well as the Moon, were subjected to increased bombardment by small and large meteorites. The result of this bombardment and an earlier collision of planetesimals could be the release of volatiles and the beginning of the formation of a secondary atmosphere, since the primary, consisting of gases captured during the formation of the Earth, most likely quickly dissipated into outer space. A little later, the hydrosphere began to form. The atmosphere and hydrosphere formed in this way were replenished in the process of degassing of the mantle during volcanic activity.

The fall of large meteorites created vast and deep craters, similar to those currently observed on the Moon, Mars, Mercury, where their traces have not been erased by subsequent changes. Cratering could provoke magma outpourings with the formation of basalt fields similar to those covering the lunar "seas". Thus, the primary crust of the Earth was probably formed, which, however, has not been preserved on its modern surface, with the exception of relatively small fragments in the “younger” crust of the continental type.

This crust, containing in its composition already granites and gneisses, however, with a lower content of silica and potassium than in "normal" granites, appeared at the turn of about 3.8 billion years and is known to us from outcrops within the crystalline shields of almost all continents. The method of formation of the oldest continental crust is still largely unclear. This crust, metamorphosed everywhere under conditions of high temperatures and pressures, contains rocks whose textural features indicate accumulation in the aquatic environment, i.e. in this distant epoch the hydrosphere already existed. The appearance of the first crust, similar to the modern one, required the supply of large amounts of silica, aluminum, and alkalis from the mantle, while now mantle magmatism creates a very limited volume of rocks enriched in these elements. It is believed that 3.5 billion years ago, gray-gneiss crust, named after the predominant type of its constituent rocks, was widespread on the area of ​​modern continents. In our country, for example, it is known on the Kola Peninsula and in Siberia, in particular in the basin of the river. Aldan.

Principles of periodization of the geological history of the Earth

Further events in geologic time are often determined according to relative geochronology, categories "old", "younger". For example, some era is older than some other. Separate segments of geological history are called (in decreasing order of their duration) zones, eras, periods, epochs, centuries. Their identification is based on the fact that geological events are imprinted in rocks, and sedimentary and volcanogenic rocks are located in layers in the earth's crust. In 1669, N. Stenoy established the law of stratification sequence, according to which the underlying layers of sedimentary rocks are older than the overlying ones, i.e. formed before them. Thanks to this, it became possible to determine the relative sequence of the formation of layers, and hence the geological events associated with them.

The main method in relative geochronology is the biostratigraphic, or paleontological, method of establishing the relative age and sequence of the occurrence of rocks. This method was proposed by W. Smith at the beginning of the 19th century, and then developed by J. Cuvier and A. Brongniard. The fact is that in most sedimentary rocks one can find the remains of animal or plant organisms. J.B. Lamarck and C. Darwin established that animals and plant organisms in the course of geological history gradually improved in the struggle for existence, adapting to changing living conditions. Some animal and plant organisms died out at certain stages of the development of the Earth, they were replaced by others, more perfect ones. Thus, according to the remains of earlier living more primitive ancestors found in some layer, one can judge the relatively older age of this layer.

Another method of geochronological separation of rocks, especially important for the separation of igneous formations of the ocean floor, is based on the property of the magnetic susceptibility of rocks and minerals formed in the Earth's magnetic field. With a change in the orientation of the rock relative to the magnetic field or the field itself, part of the "inherent" magnetization is retained, and the change in polarity is imprinted in a change in the orientation of the remanent magnetization of the rocks. Currently, a scale for the change of such epochs has been established.

Absolute geochronology - the doctrine of the measurement of geological time, expressed in ordinary absolute astronomical units(years), - determines the time of occurrence, completion and duration of all geological events, primarily the time of formation or transformation (metamorphism) of rocks and minerals, since the age of geological events is determined by their age. The main method here is the analysis of the ratio of radioactive substances and their decay products in rocks formed in different eras.

The oldest rocks are currently established in West Greenland (3.8 billion years). The oldest age (4.1 - 4.2 Ga) was obtained from zircons from Western Australia, but the zircon here occurs in a redeposited state in Mesozoic sandstones. Taking into account the concept of the simultaneity of the formation of all the planets of the solar system and the moon and the age of the most ancient meteorites (4.5-4.6 billion years) and ancient lunar rocks (4.0-4.5 billion years), the age of the Earth is assumed to be 4.6 billion years.

In 1881, at the II International Geological Congress in Bologna (Italy), the main divisions of the combined stratigraphic (for separating layered sedimentary rocks) and geochronological scales were approved. According to this scale, the history of the Earth was divided into four eras in accordance with the stages of development of the organic world: 1) Archean, or Archeozoic - the era of ancient life; 2) Paleozoic - the era of ancient life; 3) Mesozoic - the era of middle life; 4) Cenozoic - the era of new life. In 1887, the Proterozoic, the era of primary life, was singled out from the Archean era. Later the scale was improved. One of the variants of the modern geochronological scale is presented in Table. 8.1. The Archean era is divided into two parts: early (older than 3500 Ma) and late Archean; Proterozoic - also into two: early and late Proterozoic; in the latter, the Riphean (the name comes from the ancient name of the Ural Mountains) and Vendian periods are distinguished. The Phanerozoic zone is subdivided into the Paleozoic, Mesozoic and Cenozoic eras and consists of 12 periods.

Table 8.1. Geological scale

The main stages of the evolution of the earth's crust

Let us briefly consider the main stages in the evolution of the earth's crust as an inert substrate, on which the diversity of the surrounding nature has developed.

INapxee The still rather thin and plastic crust, under the influence of extension, experienced numerous discontinuities, through which basaltic magma again rushed to the surface, filling troughs hundreds of kilometers long and many tens of kilometers wide, known as greenstone belts (they owe this name to the prevailing greenschist low-temperature metamorphism of basalt breeds). Along with basalts, among the lavas of the lower, most thick part of the section of these belts, there are high-magnesian lavas, indicating a very high degree of partial melting of the mantle substance, which indicates a high heat flow, much higher than the modern one. The development of greenstone belts consisted in a change in the type of volcanism towards an increase in the content of silicon dioxide (SiO 2 ) in it, in compressional deformations and metamorphism of sedimentary-volcanogenic fulfillment, and, finally, in the accumulation of clastic sediments, indicating the formation of a mountainous relief.

After the change of several generations of greenstone belts, the Archean stage of the evolution of the earth's crust ended 3.0 -2.5 billion years ago with the massive formation of normal granites with a predominance of K 2 O over Na 2 O. Granitization, as well as regional metamorphism, which in some places reached the highest stage, led to the formation of a mature continental crust over most of the area of ​​modern continents. However, this crust turned out to be insufficiently stable: at the beginning of the Proterozoic era, it experienced crushing. At this time, a planetary network of faults and cracks arose, filled with dikes (plate-like geological bodies). One of them, the Great Dike in Zimbabwe, is over 500 km long and up to 10 km wide. In addition, rifting appeared for the first time, giving rise to zones of subsidence, powerful sedimentation and volcanism. Their evolution led to the creation at the end early Proterozoic(2.0-1.7 billion years ago) of folded systems that re-soldered the fragments of the Archean continental crust, which was facilitated by a new era of powerful granite formation.

As a result, by the end of the Early Proterozoic (by the turn of 1.7 billion years ago), a mature continental crust already existed on 60–80% of the area of ​​its modern distribution. Moreover, some scientists believe that at this turn the entire continental crust was a single massif - the supercontinent Megagea (large land), which on the other side of the globe was opposed by the ocean - the predecessor of the modern Pacific Ocean - Megathalassa (large sea). This ocean was less deep than modern oceans, because the growth of the volume of the hydrosphere due to degassing of the mantle in the process of volcanic activity continues throughout the subsequent history of the Earth, although more slowly. It is possible that the prototype of Megathalassa appeared even earlier, at the end of the Archean.

In the Catarchean and the beginning of the Archean, the first traces of life appeared - bacteria and algae, and in the late Archean, algal calcareous structures - stromatolites - spread. In the Late Archean, a radical change in the composition of the atmosphere began, and in the Early Proterozoic, a radical change in the composition of the atmosphere began: under the influence of plant life, free oxygen appeared in it, while the Catharchean and Early Archean atmosphere consisted of water vapor, CO 2 , CO, CH 4 , N, NH 3 and H 2 S with an admixture of HC1, HF and inert gases.

In the Late Proterozoic(1.7-0.6 billion years ago) Megagea began to gradually split, and this process sharply intensified at the end of the Proterozoic. Its traces are extended continental rift systems buried at the base of the sedimentary cover of ancient platforms. Its most important result was the formation of vast intercontinental mobile belts - the North Atlantic, Mediterranean, Ural-Okhotsk, which divided the continents of North America, Eastern Europe, East Asia and the largest fragment of Megagea - the southern supercontinent Gondwana. The central parts of these belts developed on the oceanic crust newly formed during rifting, i.e. the belts were ocean basins. Their depth gradually increased as the hydrosphere grew. At the same time, mobile belts developed along the periphery of the Pacific Ocean, the depth of which also increased. Climatic conditions became more contrasting, as evidenced by the appearance, especially at the end of the Proterozoic, of glacial deposits (tillites, ancient moraines, and water-glacial sediments).

Paleozoic stage The evolution of the earth's crust was characterized by the intensive development of mobile belts - intercontinental and marginal continental (the latter on the periphery of the Pacific Ocean). These belts were divided into marginal seas and island arcs, their sedimentary-volcanogenic strata experienced complex fold-thrust, and then normal-shear deformations, granites were introduced into them and on this basis folded mountain systems were formed. This process proceeded unevenly. It distinguishes a number of intense tectonic epochs and granitic magmatism: Baikal - at the very end of the Proterozoic, Salair (from the Salair ridge in Central Siberia) - at the end of the Cambrian, Takov (from the Takov mountains in the east of the USA) - at the end of the Ordovician, Caledonian ( from the ancient Roman name of Scotland) - at the end of the Silurian, Acadian (Acadia - the ancient name of the northeastern states of the USA) - in the middle of the Devonian, Sudeten - at the end of the Early Carboniferous, Saal (from the Saale River in Germany) - in the middle of the early Permian. The first three tectonic epochs of the Paleozoic are often combined into the Caledonian era of tectogenesis, the last three into the Hercynian or Varisian. In each of the listed tectonic epochs, certain parts of the mobile belts turned into folded mountain structures, and after destruction (denudation) they were part of the foundation of young platforms. But some of them partially experienced activation in subsequent epochs of mountain building.

By the end of the Paleozoic, the intercontinental mobile belts were completely closed and filled with folded systems. As a result of the withering away of the North Atlantic belt, the North American continent closed with the East European, and the latter (after the completion of the development of the Ural-Okhotsk belt) - with the Siberian, Siberian - with the Chinese-Korean. As a result, the supercontinent Laurasia was formed, and the dying off of the western part of the Mediterranean belt led to its unification with the southern supercontinent - Gondwana - into one continental block - Pangea. The eastern part of the Mediterranean belt at the end of the Paleozoic - the beginning of the Mesozoic turned into a huge bay of the Pacific Ocean, along the periphery of which folded mountain structures also rose.

Against the background of these changes in the structure and relief of the Earth, the development of life continued. The first animals appeared as early as the late Proterozoic, and at the very dawn of the Phanerozoic, almost all types of invertebrates existed, but they still lacked the shells or shells that have been known since the Cambrian. In the Silurian (or already in the Ordovician), vegetation began to land on land, and at the end of the Devonian there were forests that became most widespread in the Carboniferous period. Fish appeared in the Silurian, amphibians in the Carboniferous.

Mesozoic and Cenozoic eras - the last major stage in the development of the structure of the earth's crust, which is marked by the formation of modern oceans and the isolation of modern continents. At the beginning of the stage, in the Triassic, Pangea still existed, but already in the early Jurassic, it again split into Laurasia and Gondwana due to the emergence of the latitudinal Tethys ocean, stretching from Central America to Indochina and Indonesia, and in the west and east it merged with the Pacific Ocean (Fig. 8.6); this ocean also included the Central Atlantic. From here, at the end of the Jurassic, the process of moving apart the continents spread to the north, creating the North Atlantic during the Cretaceous period and the early Paleogene, and starting from the Paleogene, the Eurasian basin of the Arctic Ocean (the Amerasian basin arose earlier as part of the Pacific Ocean). As a result, North America separated from Eurasia. In the Late Jurassic, the formation of the Indian Ocean began, and from the beginning of the Cretaceous, the South Atlantic began to open up from the south. This meant the beginning of the disintegration of Gondwana, which existed as a whole throughout the Paleozoic. At the end of the Cretaceous, the North Atlantic joined the South, separating Africa from South America. At the same time, Australia separated from Antarctica, and at the end of the Paleogene, the latter separated from South America.

Thus, by the end of the Paleogene, all modern oceans took shape, all modern continents became isolated, and the appearance of the Earth acquired a form that was basically close to the present. However, there were no modern mountain systems yet.

From the Late Paleogene (40 million years ago), intensive mountain building began, culminating in the last 5 million years. This stage of the formation of young fold-cover mountain structures, the formation of revived arch-block mountains is distinguished as neotectonic. In fact, the neotectonic stage is a sub-stage of the Mesozoic-Cenozoic stage of the Earth's development, since it was at this stage that the main features of the modern Earth relief took shape, starting with the distribution of oceans and continents.

At this stage, the formation of the main features of modern fauna and flora was completed. The Mesozoic era was the era of reptiles, mammals began to predominate in the Cenozoic, and man appeared in the late Pliocene. At the end of the Early Cretaceous, angiosperms appeared and the land acquired grass cover. At the end of the Neogene and Anthropogene, the high latitudes of both hemispheres were covered by a powerful continental glaciation, the relics of which are the ice caps of Antarctica and Greenland. This was the third major glaciation in the Phanerozoic: the first took place in the late Ordovician, the second - at the end of the Carboniferous - the beginning of the Permian; both were common within Gondwana.

QUESTIONS FOR SELF-CHECKING

What are spheroid, ellipsoid and geoid? What are the parameters of the ellipsoid adopted in our country? Why is it needed?

What is the internal structure of the Earth? On the basis of what is the conclusion about its structure made?

What are the main physical parameters of the Earth and how do they change with depth?

What is the chemical and mineralogical composition of the Earth? On what basis is a conclusion made about the chemical composition of the entire Earth and the earth's crust?

What are the main types of the earth's crust are currently distinguished?

What is the hydrosphere? What is the water cycle in nature? What are the main processes occurring in the hydrosphere and its elements?

What is atmosphere? What is its structure? What processes take place within it? What is weather and climate?

Define endogenous processes. What endogenous processes do you know? Briefly describe them.

What is the essence of lithospheric plate tectonics? What are its main provisions?

10. Define exogenous processes. What is the main essence of these processes? What endogenous processes do you know? Briefly describe them.

11. How do endogenous and exogenous processes interact? What are the results of the interaction of these processes? What is the essence of the theories of V. Davis and V. Penk?

What are the current ideas about the origin of the Earth? How was its early formation as a planet?

On the basis of what is the periodization of the geological history of the Earth?

14. How did the earth's crust develop in the geological past of the Earth? What are the main stages in the development of the earth's crust?

LITERATURE

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Gavrilov V.P. Journey into the past of the Earth. M., 1987.

Geological dictionary. T. 1, 2. M., 1978.

GorodnitskyA. M., Zonenshain L.P., Mirlin E.G. Reconstruction of the position of the continents in the Phanerozoic. M., 1978.

7. Davydov L.K., Dmitrieva A.A., Konkina N.G. General hydrology. L., 1973.

Dynamic Geomorphology / Ed. G.S. Anan'eva, Yu.G. Simonova, A.I. Spiridonov. M., 1992.

Davis W.M. Geomorphological essays. M., 1962.

10. Earth. Introduction to general geology. M., 1974.

11. Climatology / Ed. O.A. Drozdova, N.V. Kobysheva. L., 1989.

Koronovsky N.V., Yakusheva A.F. Fundamentals of Geology. M., 1991.

Leontiev O.K., Rychagov G.I. General geomorphology. M., 1988.

Lvovich M.I. Water and life. M., 1986.

Makkaveev N.I., Chalov R.C. channel processes. M., 1986.

Mikhailov V.N., Dobrovolsky A.D. General hydrology. M., 1991.

Monin A.S. Introduction to the theory of climate. L., 1982.

Monin A.S. History of the Earth. M., 1977.

Neklyukova N.P., Dushina I.V., Rakovskaya E.M. and etc. Geography. M., 2001.

Nemkov G.I. and etc. Historical geology. M., 1974.

Restless landscape. M., 1981.

General and field geology / Ed. A.N. Pavlova. L., 1991.

Penk W. Morphological analysis. M., 1961.

Perelman A.I. Geochemistry. M., 1989.

Poltaraus B.V., Kisloe A.V. Climatology. M., 1986.

26. Problems of Theoretical Geomorphology / Ed. L.G. Nikiforova, Yu.G. Simonov. M., 1999.

Saukov A.A. Geochemistry. M., 1977.

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Ushakov S.A., Yasamanov H.A. Continental drift and the Earth's climate. M., 1984.

Khain V.E., Lomte M.G. Geotectonics with the basics of geodynamics. M., 1995.

Khain V.E., Ryabukhin A.G. History and methodology of geological sciences. M., 1997.

Khromov S.P., Petrosyants M.A. Meteorology and climatology. M., 1994.

Schukin I.S. General geomorphology. T.I. M., 1960.

Ecological functions of the lithosphere / Ed. V.T. Trofimov. M., 2000.

Yakusheva A.F., Khain V.E., Slavin V.I. General geology. M., 1988.

Archean era. The beginning of this ancient era is considered not the moment of the formation of the Earth, but the time after the formation of the solid earth's crust, when mountains and rocks already existed and the processes of erosion and sedimentation came into play. The duration of this era is approximately 2 billion years, i.e., it corresponds to all other eras taken together. The Archean era seems to have been characterized by catastrophic and widespread volcanic activity, as well as deep uplifts culminating in the formation of mountains. The high temperature, pressure and mass movements that accompanied these movements apparently destroyed most of the fossils, but some data about the life of those times still survived. In the Archeozoic rocks, graphite or pure carbon is found everywhere in scattered form, which probably represent altered remains of animals and plants. If we accept that the amount of graphite in these rocks reflects the amount of living matter (and this, apparently, is true), then in the Archaean this living matter probably existed very much, since there is more carbon in the rocks of this age than in coal seams of the Appalachian Basin.

Proterozoic era. The second era, lasting about 1 billion years, was characterized by the deposition of a large amount of precipitation and at least one significant glaciation, during which ice sheets extended to latitudes less than 20 ° from the equator. A very small number of fossils were found in the Proterozoic rocks, which, however, testify not only to the existence of life in this era, but also to the fact that evolutionary development advanced far ahead by the end of the Proterozoic. Spicules of sponges, remains of jellyfish, fungi, algae, brachiopods, arthropods, etc. have been found in Proterozoic deposits.

Palaeozoic. Between the deposits of the Upper Proterozoic and the initial layers of the third, Paleozoic era, there is a significant break caused by mountain building movements. For 370 million years of the Paleozoic era, representatives of all types and classes of animals appeared, with the exception of birds and mammals. Since different species of animals existed only for certain periods of time, their fossils allow geologists to compare deposits of the same age found in different places.

• Cambrian period [show] .

  Cambrian period- the most ancient department of the Paleozoic era; It is represented by rocks abounding in fossils, so that the appearance of the Earth at this time can be reconstructed with sufficient accuracy. The forms that lived during this period were so diverse and complex that they must have descended from ancestors that existed at least in the Proterozoic, and possibly in the Archaean.

  All modern types of animals, with the exception of chordates, already existed and all plants and animals lived in the sea (the continents, apparently, were lifeless deserts until the late Ordovician or Silurian, when plants moved to land). There were primitive, shrimp-like crustaceans and forms resembling arachnids; some of their descendants have survived, almost unchanged, to the present day (horse crabs). The seabed was covered with solitary sponges, corals, stalked echinoderms, gastropods and bivalves, primitive cephalopods, brachiopods and trilobites.

  Brachiopods - sessile animals with a bivalve shell and feeding on plankton, flourished in the Cambrian and in all other systems of the Paleozoic.

  Trilobites are primitive arthropods with an elongated flat body, covered on the dorsal side with a hard shell. Two grooves stretch along the shell, dividing the body into three parts, or lobes. Each body segment, with the exception of the very last, bears a pair of biramous limbs; one of them served for walking or swimming and it had a gill. Most trilobites were 5-7.5 cm long, but some reached 60 cm.

  In the Cambrian, both unicellular and multicellular algae existed. One of the best preserved collections of Cambrian fossils was collected in the mountains of British Columbia. It includes worms, crustaceans, and a transitional form between worms and arthropods, similar to the living peripatus.

  After the Cambrian, evolution was mainly characterized not by the emergence of completely new types of structure, but by the branching of existing lines of development and the replacement of the original primitive forms by more highly organized ones. It is probable that pre-existing forms have reached such a degree of adaptability to the environment that they have acquired a significant preponderance over any new, unadapted types.

• Ordovician period [show] .

  During the Cambrian period, the continents began to gradually sink into the water, and in the Ordovician period this sinking reached its maximum, so that a significant part of the current land was covered with shallow seas. Huge cephalopods lived in these seas - animals similar to squid and nautilus - with a straight shell from 4.5 to 6 m long and 30 cm in diameter.

  The Ordovician seas must have been very warm, as warm-water corals spread as far as Lake Ontario and Greenland at this time.

  The first remains of vertebrates were found in the Ordovician deposits. These small animals, called corymbs, were bottom forms, devoid of jaws and paired fins (Fig. 1.). Their carapace consisted of heavy bony plates on the head and thick scales on the body and tail. Otherwise, they were similar to modern lampreys. They apparently lived in fresh water, and their shell served to protect against giant predatory water scorpions called eurypterids, which also lived in fresh water.

• Silurian [show] .

  The Silurian period saw two events of great biological significance: the development of land plants and the appearance of air-breathing animals.

  The first land plants seem to have been more like ferns than mosses; ferns were the dominant plants also in the subsequent Devonian and lower Carboniferous.

  The first air-breathing land animals were arachnids, somewhat reminiscent of modern scorpions.

  The continents that had been low during the Cambrian and Ordovician times rose, especially in Scotland and northeastern North America, and the climate became much cooler.

• Devonian [show] .

  

  

  

  During the Devonian, the first armored fishes gave rise to many different fishes, so that this period is often called the "time of the fishes."

  Jaws and paired fins first developed in armored sharks (Placodermi), which were small, shelled freshwater forms. These animals were characterized by a variable number of paired fins. Some had two pairs of fins, corresponding to the fore and hind limbs of higher animals, while others had up to five pairs of additional fins between these two pairs.

  During the Devonian, real sharks appeared in fresh waters, which showed a tendency to migrate to the ocean and to lose their bulky bone carapace.

  The ancestors of bony fishes also originated in Devonian freshwater streams; by the middle of this period, they had a division into three main types: lungfish, lobe-finned and ray-finned. All these fish had lungs and a shell of bony scales. Only a very few lungfish have survived to this day, and the ray-finned, having gone through a period of slow evolution throughout the remainder of the Paleozoic era and the beginning of the Mesozoic, later, in the Mesozoic, experienced significant divergence and gave rise to modern bony fish (Teleostei).

  The lobe-finned fish, which were the ancestors of terrestrial vertebrates, almost died out by the end of the Paleozoic and, as previously believed, disappeared completely at the end of the Mesozoic. However, in 1939 and 1952 off the east coast of South Africa, live representatives of the lobe-finned about 1.5 m long were caught.

  The upper part of the Devonian was marked by the appearance of the first terrestrial vertebrates - amphibians called stegocephali (meaning "covered heads"). These animals, whose skulls were covered with a bony shell, are in many respects similar to lobe-finned fish, differing from them mainly in the presence of limbs, and not fins.

  The Devonian is the first period that is characterized by true forests. During this period, ferns, club mosses, ferns and primitive gymnosperms flourished - the so-called "seed ferns". It is believed that insects and centipedes arose in the Late Devonian.

• Carboniferous period [show] .

  At this time, large swampy forests were widespread, the remains of which gave rise to the main coal deposits of the world. The continents were covered with low-lying swamps overgrown with ferns, common ferns, seed ferns and broad-leaved evergreens.

  

  

  The first reptiles, called whole-skull and similar to the amphibians that preceded them, appeared in the second half of the Carboniferous period, flourished in the Permian - the last period of the Paleozoic - and died out at the beginning of the Mesozoic era. It is not clear what the most primitive of the reptiles known to us Seymouria (named after the city in Texas near which its fossils were found) was - an amphibian, ready to turn into a reptile, or a reptile that had just stepped over the border separating it from amphibians .

  One of the main differences between amphibians and reptiles is the structure of the eggs they lay. Amphibians lay their eggs, covered with a gelatinous membrane, in the water, and reptiles lay their eggs, covered with a strong shell, on the ground. Since the eggs of Seymouria have not been preserved, we may never be able to decide which class this animal should be placed in.

  Seymouria was a large slow lizard-like form. Its short, stump-like legs extended horizontally away from the body, like a salamander's, instead of squeezing closer and going straight down to form column-like supports for the body.

  During the Carboniferous period, two important groups of winged insects appeared - the ancestors of cockroaches, which reached 10 cm in length, and the ancestors of dragonflies, some of which had a wingspan of 75 cm.

• Permian period [show] .

  

  

  The last period of the Paleozoic was characterized by major changes in climate and topography. Continents have risen all over the globe, so that the shallow seas that covered the region from Nebraska to Texas have dried up, leaving behind a salty desert. At the end of the Permian, widespread folding, known as the Hercynian orogeny, took place, during which a large mountain range from Nova Scotia to Alabama was uplifted. This range was originally higher than the modern Rocky Mountains. At the same time, other mountain ranges were forming in Europe.

  Enormous ice sheets extending from the Antarctic covered most of the southern hemisphere, extending into Africa and Brazil almost to the equator.

  North America was one of the few areas that did not undergo glaciation at this time, but even here the climate became much colder and drier than it had been during most of the Paleozoic era. Many Paleozoic organisms, apparently, could not adapt to climate change and died out during the Hercynian orogeny. Due to the cooling of water and the reduction of space suitable for life, as a result of the drying up of shallow seas, even many marine forms have become extinct.

  From the primitive whole-cranial during the Late Carboniferous and Early Permian, that group of reptiles developed from which mammals are believed to have descended in a straight line. These were pelycosaurs - predatory reptiles with a more slender and lizard-like body than those of whole-skull.

  In the late Permian, another group of reptiles, the therapsids, probably developed from pelycosaurs, possessing several other mammalian features. One of the representatives of this group - Cynognathus (reptile with a "dog's jaw") was a slender, light animal about 1.5 m long, with a skull intermediate in character between that of a reptile and a mammal. Its teeth, instead of being conical and identical, as is characteristic of reptiles, differentiated into incisors, canines and molars. Since we have no information about the soft parts of the animal, whether it was covered with scales or hair, whether it was warm-blooded or cold-blooded, and whether it suckled its young, we call it reptile. However, if we had more complete data, it might have to be considered a very early mammal. Therapsids, widespread in the late Permian, were replaced by many other reptiles at the beginning of the Mesozoic.

Mesozoic era (time of reptiles). The Mesozoic era, which began about 230 million years ago and lasted about 167 million years, is divided into three periods:

1. Triassic
2. Jurassic
3. chalky

During the Triassic and Jurassic periods, most of the continental regions were raised above sea level. In the Triassic, the climate was dry, but warmer than in the Permian, and in the Jurassic, it was warmer and more humid than in the Triassic. The trees of the famous Stone Forest in Arizona have been around since the Triassic period.

During the Cretaceous period, the Gulf of Mexico, expanding, flooded Texas and New Mexico, and in general the sea gradually moved towards the continents. In addition, vast swamps have developed in the area stretching from Colorado to British Columbia. At the end of the Cretaceous, the interior of the North American continent experienced further subsidence, so that the waters of the Gulf of Mexico basin joined with the waters of the Arctic basin and divided this continent into two parts. The Cretaceous ended with a great uplift called the Alpine orogeny, during which the Rocky Mountains, the Alps, the Himalayas, and the Andes arose, and which gave rise to volcanic activity in western North America.

The evolution of reptiles . The emergence, differentiation and finally extinction of a great number of reptiles belonging to the six main branches are the most characteristic feature of the Mesozoic era. [show] .

The most primitive branch includes, in addition to the ancient whole-skull, turtles that arose in Perm. Turtles have developed the most complex (among land animals) shell; it consists of plates of epidermal origin, fused with the underlying ribs and breastbone. With this protective device, both sea turtles and tortoises survived from pre-dinosaur times with only a few structural changes. The legs of the turtles, which extend from the body in a horizontal direction, which makes it difficult and slow to move, and their skulls, which do not have holes behind the eye sockets, were inherited unchanged from the ancient whole-cranial ones.

The second group of reptiles, coming with relatively few changes from the ancestral whole-skull, are lizards, the most numerous among living reptiles, as well as snakes. Lizards have for the most part retained a primitive type of movement with horizontally diverging legs, although many of them can run quickly. In most cases, they are small, but the Indian monitor lizard reaches 3.6 m in length, and some fossil forms are 7.5 m long. Cretaceous mosasaurs were sea lizards that reached 12 m in length; they had a long tail used for swimming.

During the Cretaceous period, snakes evolved from lizard ancestors. The essential difference between snakes and lizards is not the loss of legs (some lizards also lack legs), but certain changes in the structure of the skull and jaws that allow snakes to open their mouths wide enough to swallow animals larger than themselves.

The representative of the ancient branch, somehow managed to survive to this day in New Zealand, is the tuatara (Shpenodon punctatum). It shares several features with its cotylosaur ancestors; one such feature is the presence of a third eye at the top of the skull.

The main group of Mesozoic reptiles were the archosaurs, the only living representatives of which are alligators and crocodiles. At some early point in their evolution, archosaurs, then 1.5 meters long, adapted to walking on two legs. Their front legs shortened, while their hind legs lengthened, strengthened and greatly changed their shape. These animals rested and walked on all four legs, but in critical circumstances they reared up and ran on two hind legs, using their rather long tail as a balance.

Many different specialized forms evolved from early archosaurs, some of which continued to walk on two legs while others returned to walking on all fours. These descendants include phytosaurs - aquatic, alligator-like reptiles common in the Triassic; crocodiles, which formed in the Jurassic and replaced phytosaurs as aquatic forms; and finally, pterosaurs, or flying reptiles, which included animals the size of robins, as well as the largest animal ever flying, Pteranodon, with a wingspan of 8 m

There were two types of flying reptiles; some had a long tail, equipped with a tail blade at the end, others had a short tail. Representatives of both types, apparently, fed on fish and probably flew long distances over water in search of food. Their legs were not adapted for standing, and therefore it is assumed that they, like bats, rested in a suspended state, clinging to some kind of support.

Of all the branches of reptiles, dinosaurs are the most famous, which means "terrible lizards" in translation. They were divided into two main types: ornithischians and lizards.

Saurischia (lizards) first appeared in the Triassic and continued to exist until the Cretaceous. The early lizards were fast, predatory, rooster-sized, bipedal forms that probably preyed on lizards and primitive mammals that had already appeared. During the Jurassic and Cretaceous, this group showed an increasing trend in size, culminating in the giant Cretaceous predator Tyrannosaurus Rex. Other Saurischia, which appeared in the late Triassic, switched to plant foods, again began to walk on four legs, and during the Jurassic and Cretaceous gave rise to a number of giant forms that led an amphibious lifestyle. These largest four-legged animals that have ever lived include brontosaurs up to 20 m long, diplodocus, which reached a length of over 25 m, and brachiosaurus, the largest of all, whose weight is estimated at 50 tons.

Another group of dinosaurs, the Ornitischia (Ornithischians), were herbivores, probably from the very beginning of their evolution. Although some of them walked on their hind legs, most moved on all four legs. Instead of missing front teeth, they developed a strong horny sheath, similar to a bird's beak, which in some forms was wide and flat, like ducks (hence the name "duck-billed" dinosaurs). This type is characterized by webbed feet. Other species developed large armored plates that protected them from predatory lizards. The ankylosaurus, which is called the "reptile tank", had a wide flat body covered with bone plates and large spikes protruding from the sides.

Finally, some Cretaceous ornithischians developed bony plates around their heads and necks. One of them, Triceratops, had two horns above the eyes and a third above the nasal region - all up to almost 1 m long.

Two other groups of Mesozoic reptiles that differ both from each other and from dinosaurs are marine plesiosaurs and ichthyosaurs. The first were characterized by an extremely long neck, which was more than half the length of the animal. Their body was wide, flat, resembling the body of a turtle, and their tail was short. Plesiosaurs swam with flipper-like limbs. Often they reached 13-14 m in length.

Ichthyosaurs (lizard fish) were similar in appearance to fish or whales, with a short neck, a large dorsal fin, and a shark-type tail. They swam with swift tail movements, using their limbs only as controls. It is believed that ichthyosaur cubs were born alive, hatching from an egg in the mother's body, since adults were too specialized and could not go on land to lay eggs, and reptile eggs drown in water. The finding of juvenile skeletons inside the abdominal cavity of adult fossils supports this theory.

At the end of the Cretaceous, many reptiles died out. They obviously could not adapt to the significant changes in environmental conditions caused by the Alpine orogeny. As the climate became colder and drier, many plants that served as food for herbivorous reptiles disappeared. Some herbivorous reptiles were too bulky to move on land when the swamps dried up. The smaller, warm-blooded mammals that had already appeared had an advantage in the competition for food, and many of them even fed on reptile eggs. The extinction of many reptiles was probably the result of the combined action of a number of factors or any one factor.

Other directions of evolution in the Mesozoic . Although reptiles were the dominant animals in the Mesozoic, many other important organisms also developed at this time. [show] .

In the Mesozoic, the number and diversity of gastropods and bivalves increased. Sea urchins have reached the highest point of their development.

In the Triassic, mammals arose, and in the Jurassic, bony fish and birds arose.

Most modern orders of insects appeared in the early Mesozoic.

During the early Triassic, seed ferns, cycads, and conifers were the most common plants, but by the Cretaceous, many other forms resembling modern species appeared - fig trees, magnolias, palm trees, maples and oaks.

From the Jurassic time, magnificent imprints of the most ancient species of birds have been preserved, on which even the outlines of feathers are visible. This creature, called Archeopteryx, was about the size of a crow and had rather weak wings, jaws armed with teeth, and a long reptilian tail covered with feathers.

Fossils of two other birds, Hesperornis and Ichthyornis, have been found in the Cretaceous deposits. The first is an aquatic diving bird that has lost the ability to fly, and the second is a strong flying bird with reptilian teeth, about the size of a dove.

Modern toothless birds formed at the beginning of the next era.

Cenozoic era (time of mammals). The Cenozoic era can justifiably be called the time of birds, the time of insects, or the time of flowering plants, since the development of all these organisms is no less characteristic of it than the development of mammals. It covers the period from the Alpine orogeny (about 63 million years ago) to the present day and is divided into two periods - the Tertiary, which lasted about 62 million years, and the Quaternary, which includes the last 1-1.5 million years.

• Tertiary period. This period is subdivided into five epochs: Paleocene, Eocene, Oligocene, Miocene and Pliocene. The rocky mountains formed at the beginning of the Tertiary period were already strongly eroded by the Oligocene, as a result of which the North American continent acquired a gently undulating relief.

  In the Miocene, another series of uplifts created the Sierra Nevada mountains and new ranges in the Rocky Mountains, which led to the formation of deserts in the west. The climate in the Oligocene was milder than at present, so that palm trees spread as far north as Wyoming.

  The uplift, which began in the Miocene, continued into the Pliocene and, combined with the glaciations of the Pleistocene time, led to the extinction of many pre-existing mammals and other animals. The final uplift of the Colorado Plateau, which created the Grand Canyon, almost ended in a short time of the Pleistocene and modern epochs.

  The oldest fossils of true mammals date back to the Late Triassic, and in the Jurassic, there were already four orders of mammals, all of which were the size of a rat or a small dog.

  The earliest mammals (monotrems) were oviparous animals, and their only representatives that have survived to this day are the platypus and the needle-covered echidna living in Australia. Both of these forms have a coat, and they feed their young with milk, but they also lay eggs, like turtles. The ancestral egg-laying mammals, of course, must have been different from the specialized platypus and echidna, but the fossil record of these ancient forms is incomplete. Living monotremes could only last so long because they lived in Australia, where until recently there were no placental mammals, so they had no one to compete with.

  In the Jurassic and Cretaceous, most mammals were already highly organized enough to produce live young, although in the most primitive of them - the marsupials - the young are born underdeveloped and must remain for several months in the pouch on the mother's abdomen, where the nipples are located. Australian marsupials, like monotremes, did not meet competition from more adapted placental mammals, while on other continents this competition led to the extinction of marsupials and monotremes; therefore, in Australia, marsupials, as a result of divergent development, gave rise to many different forms, outwardly resembling some placentals. There are marsupial mice, shrews, cats, moles, bears, and one kind of wolf, as well as a number of forms that have no placental parallels, such as kangaroos, wombats, and wallabies.

  During the Pleistocene, giant kangaroos and rhinoceros-sized wombats lived in Australia. Opossums are more similar to primitive ancestral marsupials than any of these more specialized forms; they are the only marsupials found outside of Australia and South America.

  Modern highly organized placental mammals, which include humans, characterized by the birth of live young capable of independent existence, descended from insectivorous arboreal ancestors. Fossils of this ancestral form, found in the Cretaceous deposits, show that it was a very small animal, like the living shrew. Some of these ancestral mammals retained an arboreal way of life and, through a series of intermediate forms, gave rise to primates - monkeys and humans. Others lived on the ground or underground, and during the Paleocene all other mammals living today are descended from them.

  Primitive Paleocene mammals had conical reptilian teeth, five-fingered limbs, and a small brain. Also, they were plantigrade, not digitigrade.

  During the Tertiary period, the evolution of herbaceous plants, which served as food, and forests, which sheltered animals, was the most important factor influencing the change in the structure of the body of mammals. Along with a tendency to increase in size, the development of all mammals showed a bias towards an increase in the relative size of the brain and changes in teeth and legs. When new, more adapted forms appeared, primitive mammals died out.

  Although fossil remains of both marsupials and placentals were found in the Cretaceous deposits, the discovery of highly developed mammals in the Early Tertiary deposits was rather unexpected. Whether they really arose at this time or whether they existed earlier in the highlands and simply did not survive as fossils is not known.

  In the Paleocene and Eocene, the first predators, called creodonts, originated from primitive insectivorous placentals. In the Eocene and Oligocene, they were replaced by more modern forms, which over time gave rise to living predators, such as cats, dogs, bears, weasels, as well as pinniped marine predators - seals and walruses.

  

  One of the best-known fossil predators is the saber-toothed tiger, which became extinct only recently, in the Pleistocene. It had extremely long and sharp upper fangs, and the lower jaw could swing down and to the side so that the fangs pierced the prey like sabers.

  Large herbivorous mammals, in most cases with hooves, are sometimes combined into one group called ungulates. However, they are not a single natural group, but consist of several independent branches, so that a cow and a horse, despite the fact that they both have hooves, are no more related to each other than each of them is to a tiger. The molars of ungulates are flattened and enlarged, which facilitates the grinding of leaves and grass. Their legs became long and adapted to the fast running necessary to escape from predators.

  The oldest ungulates, called Condylarthra, appeared in the Paleocene. They had a long body and a long tail, flat grinding molars, and short legs ending in five toes with a hoof on each. A group analogous to primitive predators - creodonts, were primitive ungulates called wintatheria. In the Paleocene and Eocene, some of them reached the size of an elephant, while others had three large horns extending from the top of the head.

  The paleontological record of several evolutionary lines of ungulates - horses, camels and elephants - is so complete that it is possible to trace the entire development of these animals from small primitive five-fingered forms. The main direction of evolution in ungulates was towards an increase in the overall size of the body and a decrease in the number of fingers. Ungulates early fell into two groups, one of which is characterized by an even number of fingers and includes cows, sheep, camels, deer, giraffe, pigs and hippos. Another group is characterized by an odd number of fingers and includes horses, zebras, tapirs and rhinos.

  The development of elephants and their recently extinct relatives - mammoths and mastodons - can be traced back centuries to the Eocene ancestor, which was the size of a pig and did not have a trunk. This primitive form, called Moeritherium, was close to the trunk, from which branched, in addition, such dissimilar forms as hyraxes (a small marmot-like animal found in Africa and Asia) and a sea cow.

  Whales and dolphins are descended from Eocene cetacean forms called zeiglodonts, and these latter in turn are believed to have descended from creodonts.

  The evolution of bats can be traced back to winged animals that lived in the Eocene and were descendants of primitive insectivores.

  The evolution of some other mammals - rodents, rabbits and edentulous (anteaters, sloths and armadillos) - is less well known.

• Quaternary period (human time). The Quaternary period, which covers the last 1-1.5 million years, is usually divided into two epochs - Pleistocene and modern. The latter began approximately 11,000 years ago, from the moment the last glacier retreated. The Pleistocene is characterized by four ice ages, separated by intervals when the glaciers retreated. At the time of maximum distribution, ice sheets occupied almost 10 million square meters in North America. km, extending south to the Ohio and Missouri rivers. The Great Lakes, which have been plowed by moving glaciers, have drastically changed their outlines many times and from time to time connected with the Mississippi. It has been estimated that in the past, when the Mississippi collected water from the lakes, to Duluth in the west and to Buffalo in the east, its discharge was more than 60 times its present day. During the Pleistocene glaciations, such an amount of water was removed from the sea and turned into ice that the sea level dropped by 60-90 m. England and the European mainland.

  Plants and animals of the Pleistocene era were similar to those of our time. It is sometimes difficult to distinguish Pleistocene deposits from Pliocene deposits as well, since the organisms they contain are similar both to each other and to modern forms. During the Pleistocene, after the appearance of primitive man, many mammals became extinct, including the saber-toothed tiger, the mammoth, and the giant ground sloth. The Pleistocene also saw the extinction of many plant species, especially forest species, and the appearance of numerous herbaceous forms.

  The fossil record leaves no doubt that living species evolved from pre-existing other species. This chronicle is not equally clear for all lines of evolution. Plant tissues are in most cases too soft to give good fossils, and the intermediate forms that serve as links between different types of animals were obviously forms without a skeleton, and no traces of them remain. For many evolutionary lines, in particular for vertebrates, successive stages of development are well known. Other lines have gaps that future paleontologists will have to fill.

The course and direction of the process of the emergence of species in accordance with the main provisions of the theory of evolution of Charles Darwin are supported by data from various branches of biology, including data from the field of paleontology, which serve as material evidence, since they are based on the study of fossil remains of once living organisms. As a result of the progressive development of life, some groups of organisms were replaced by others, while the third changed little, and the fourth died out. Based on the finds of fossil forms in the deposits of earth layers, it is possible to trace the true history of living nature. Thus, the paleontological series of the horse (V. O. Koralevsky), the elephant, some birds, mollusks, and others were created - from the most primitive initial forms to their modern representatives. The use of the radioisotope method makes it possible to determine with great accuracy the age of rocks in the places of occurrence of paleontological remains and the age of fossil organisms.

Based on paleontological data, the entire history of life on Earth is divided into eras and periods.

Table 1. Geochronological scale

1. Archean era- the oldest stage in the history of the Earth, when life arose in the waters of the primary seas, which was originally presented precellular its forms and the first cellular organisms. Wasp analysis of this age shows that bacteria and blue-greens lived in the aquatic environment.

2 . Proterozoic era. On the verge of the Archean and Proterozoic eras, the structure and function of organisms became more complex: multicellularity arose, a sexual process that increased the genetic heterogeneity of organisms and provided extensive material for selection; photosynthetic plants became more diverse. The multicellularity of organisms was accompanied by an increase in the specialization of cells, their association into tissues and functional systems.

It is quite difficult to trace in detail the evolution of animals and plants in the Proterozoic era due to the recrystallization of sedimentary rocks and the destruction of organic remains. In the sediments of this era, only imprints of bacteria, algae, lower types of invertebrates and lower chordates. A major step in evolution was the emergence of organisms with bilateral symmetry of the body, differentiated into the anterior and posterior sections, left and right sides, and the isolation of the dorsal and ventral surfaces. The dorsal surface of the animals served as protection, and the mouth and food capture organs were located on the abdominal surface.

3. Paleozoic era. The animal and plant world has reached a great diversity, terrestrial life began to develop.

There are six periods in the Paleozoic: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian. In the Cambrian period, life was concentrated in water (it covered a significant part of our planet) and was represented by more advanced multicellular algae, having a dissected thallus, thanks to which they more actively synthesized organic substances and were the original branch for terrestrial leafy plants. Invertebrates are widespread in the seas, including brachiopods, and from arthropods - trilobites. An independent type of two-layer animals of that period were archaeocyates, which formed reefs in ancient seas. They died out without leaving any descendants. Only lived on land bacteria And mushrooms.

In the Ordovician period, the climate was warm even in the Arctic. In fresh and brackish waters of this period, planktonic seaweed, various corals from the type of coelenterates, there were representatives of almost all types invertebrates including trilobites, mollusks, echinoderms. Bacteria were widely represented. The first representatives of jawless vertebrates appear - shield.

At the end of the Silurian period, in connection with mountain-building processes and a reduction in the area of ​​the seas, part of the algae found themselves in new environmental conditions - in shallow water bodies and on land. Many of them died. However, as a result of multidirectional variability and selection, individual representatives acquired traits that contributed to survival in new conditions. The first terrestrial spore plants appeared - psilophytes. They had a cylindrical stem about 25 cm high, instead of leaves - scales. Their most important adaptations are the appearance of integumentary and mechanical tissues, root-like outgrowths - rhizoids, as well as the elementary conducting system.

In the Devonian, the number of psilophytes declined sharply, they were replaced by their transformed descendants, higher plants - lycopsid, mossy And ferns, which develop real vegetative organs (root, stem, leaf). The emergence of vegetative organs increased the efficiency of the function of individual parts of plants and their vitality as a harmoniously integrated system. The emergence of plants on land preceded the emergence of animals. On Earth, plants accumulated biomass, and in the atmosphere - a supply of oxygen. The first inhabitants of land from invertebrates were spiders, scorpions, centipedes. There were many fish in the Devonian seas, among them - jawed armored, having an internal cartilaginous skeleton and an external strong shell, movable jaws, paired fins. Freshwater bodies inhabited lobe-finned fish that had gill and primitive pulmonary respiration. With the help of fleshy fins, they moved along the bottom of the reservoir, and when they dried up, crawled into other reservoirs. A group of lobe-finned fish was the ancestors of ancient amphibians - stegocephalians. Stegocephals lived in swampy areas, went out onto land, but bred only in water.

In the Carboniferous period, giant ferns spread, which, in a warm, humid climate, settled everywhere. During this period they flourished ancient amphibians.

During the Permian period, the climate became drier and colder, which led to the extinction of many amphibians. By the end of the period, the number of amphibian species began to decline sharply, and only small amphibians (newts, frogs, toads) have survived to this day. Tree-like spore-like ferns have been replaced by seed ferns, giving rise to gymnosperms. The latter had a developed tap root system and seeds, and their fertilization took place in the absence of water. Extinct amphibians were replaced by a more progressive group of animals descended from stegocephals - reptiles. They had dry skin, denser cellular lungs, internal fertilization, egg nutrient storage, protective egg shells.

4. Mesozoic era includes three periods: Triassic, Jurassic, Cretaceous.

Widespread in the Triassic gymnosperms, especially conifers, which have taken a dominant position. At the same time, they spread widely reptiles: ichthyosaurs lived in the seas, plesiosaurs in the air - flying pangolins, reptiles were also diversely represented on earth. Giant reptiles (brontosaurs, diplodocus, etc.) soon became extinct. At the very beginning of the Triassic, a group of small animals with a more perfect structure of the skeleton and teeth separated from the reptiles. These animals acquired the ability to live birth, a constant body temperature, they had a four-chambered heart and a number of other progressive features of organization. These were the first primitive mammals.
In the sediments of the Jurassic period of the Mesozoic o6, the remains of the first bird were also found - Archeopteryx. It combined in its structure the signs of birds and reptiles.

In the Cretaceous period of the Mesozoic, a branch of plants separated from gymnosperms, which had an organ of seed reproduction - a flower. After fertilization, the ovary of the flower turns into a fruit, so the developing seeds inside the fruit are protected by pulp and shells from adverse environmental conditions. The variety of flowers of various adaptations for pollination and distribution of fruits and seeds made it possible angiosperms (flowering) plants to spread widely in nature and take a dominant position. In parallel with them, a group of arthropods developed - insects which, being pollinators of flowering plants, contributed greatly to their progressive evolution. In the same period, there appeared real birds And placental mammals. Signs of a high degree of organization in them - a constant body temperature | complete separation of arterial and venous blood flow, increased metabolism, perfect thermoregulation, and in mammals, in addition, live birth, feeding of young with milk, development of the cerebral cortex - allowed these groups to also occupy a dominant position on Earth.

5. Cenozoic era It is divided into three periods: Paleogene, Neogene and Quaternary.

In the Paleogene, Neogene and the beginning of the Quaternary period, flowering plants, thanks to the acquisition of numerous private adaptations, occupied most of the land and represented the subtropical and tropical flora. Due to the cooling caused by the advance of the glacier, the subtropical flora retreated to the south. In the composition of the terrestrial vegetation of temperate latitudes, deciduous trees, adapted to the seasonal rhythm of temperatures, as well as shrubs and herbaceous plants. The flowering of herbaceous plants falls on the Quaternary period. Warm-blooded animals are widely distributed:
birds and mammals. Cave bears, lions, mammoths, woolly rhinoceroses lived during the ice age, which gradually died out after the retreat of the glaciers and the warming of the climate, and the animal world acquired a modern look.

The main event of this era is the formation of man. By the end of the Neogene, small tailed mammals lived in the forests - lemurs And tarsiers. From them came the ancient forms of monkeys - parapithecus, who led an arboreal lifestyle and fed on plants and insects. Their distant descendants are now living gibbons, orangutans and extinct small tree monkeys - dryopithecus. Dryopithecus gave rise to three lines of development that led to chimpanzee, gorilla, as well as extinct Australopithecus. Descended from Australopithecus at the end of the Neogene reasonable person.