Hello! In this article I want to tell you about the geochronological column. This is a column of periods of the Earth's development. And also in more detail about each era, thanks to which you can paint a picture of the formation of the Earth throughout its history. What types of life appeared first, how they changed, and how much it took.

The geological history of the Earth is divided into large intervals - eras, eras are divided into periods, periods are divided into epochs. This division was associated with events that took place on. Change abiotic environment influenced evolution organic world on Earth.

Geological eras of the Earth, or geochronological scale:

And now about everything in more detail:

Designations:
Eras;
Periods;
Epochs.

1. Catarchaean era (from the creation of the Earth, about 5 billion years ago, to the origin of life);

2. Archean era , the most ancient era (3.5 billion - 1.9 billion years ago);

3. Proterozoic era (1.9 billion – 570 million years ago);

The Archean and Proterozoic are still combined into the Precambrian. The Precambrian covers the largest portion of geological time. Areas of land and sea were formed, and active volcanic activity occurred. Shields of all continents were formed from Precambrian rocks. Traces of life are usually rare.

4. Palaeozoic (570 million - 225 million years ago) with such periods :

Cambrian period(from the Latin name for Wales)(570 million – 480 million years ago);

The transition to the Cambrian was marked by the unexpected appearance of a huge number of fossils. This is a sign of the beginning of the Paleozoic era. Marine flora and fauna flourished in numerous shallow seas. Trilobites were especially widespread.

Ordovician period(from the British Ordovician tribe)(480 million – 420 million years ago);

Much of the Earth was soft, and most of the surface was still covered by seas. The accumulation of sedimentary rocks continued, and mountain building occurred. There were reef-formers. There is an abundance of corals, sponges and mollusks.

Silurian (from the British Silure tribe)(420 million – 400 million years ago);

Dramatic events in the history of the Earth began with the development of jawless fish-like fish (the first vertebrates), which appeared in the Ordovician. Another significant event was the appearance of the first land animals in the Late Silurian.

Devonian (from Devonshire in England)(400 million – 320 million years ago);

In the Early Devonian, mountain-building movements reached their peak, but basically it was a period of spasmodic development. The first seed plants settled on land. A large variety and number of fish-like species were noted, and the first terrestrial animals developed. animals- amphibians.

Carboniferous or Carboniferous period (from the abundance of coal in the seams) (320 million – 270 million years ago);

Mountain building, folding, and erosion continued. IN North America and swampy forests and river deltas were flooded, and large coal deposits were formed. The southern continents were covered by glaciation. Insects spread rapidly, and the first reptiles appeared.

Permian period (from the Russian city of Perm)(270 million – 225 million years ago);

On a large part of Pangea - the supercontinent that united everything - conditions prevailed. Reptiles spread widely and modern insects evolved. New terrestrial flora developed, including conifers. Several marine species have disappeared.

5. Mesozoic era (225 million - 70 million years ago) with such periods:

Triassic (from the tripartite division of the period proposed in Germany)(225 million – 185 million years ago);

With the onset of the Mesozoic era, Pangea began to disintegrate. On land, the dominance of conifers was established. Diversity among reptiles was noted, with the first dinosaurs and giant marine reptiles appearing. Primitive mammals evolved.

Jurassic period(from mountains in Europe)(185 million – 140 million years ago);

Significant volcanic activity was associated with the formation of the Atlantic Ocean. Dinosaurs dominated on land, flying reptiles and primitive birds conquered the air ocean. There are traces of the first flowering plants.

Cretaceous period (from the word "chalk")(140 million – 70 million years ago);

During the maximum expansion of the seas, chalk was deposited, especially in Britain. The dominance of dinosaurs continued until the extinction of them and other species at the end of the period.

6. Cenozoic era (70 million years ago - up to our time) with such periods And epochs:

Paleogene period (70 million – 25 million years ago);

— Paleocene epoch ("the oldest part of the new epoch")(70 million – 54 million years ago);
— Eocene Epoch ("dawn of a new era")(54 million – 38 million years ago);
— Oligocene Epoch ("not very new")(38 million – 25 million years ago);

Neogene period (25 million - 1 million years ago);

— Miocene Epoch ("relatively new")(25 million – 8 million years ago);
— Pliocene Epoch ("very recent")(8 million – 1 million years ago);

The Paleocene and Neogene periods are still combined into the Tertiary period. With the onset of the Cenozoic era (new life), mammals began to spread spasmodically. Many large species evolved, although many became extinct. The number of flowering plants has increased sharply plants. As the climate cooled, herbaceous plants appeared. There was a significant uplift of the land.

Quaternary period (1 million – our time);

— Pleistocene epoch (“most recent”)(1 million – 20 thousand years ago);

— Holocene era(“a completely new era”) (20 thousand years ago – our time).

This is the last geological period that includes the present time. Four major glaciations alternated with warming periods. The number of mammals has increased; they have adapted to . The formation of man - the future ruler of the Earth - took place.

There are also other ways of dividing eras, epochs, periods, eons are added to them, and some epochs are still divided, like on this table, for example.

But this table is more complex, the confusing dating of some eras is purely chronological, not based on stratigraphy. Stratigraphy is the science of determining the relative geological age of sedimentary rocks, the division of rock strata, and the correlation of various geological formations.

This division, of course, is relative, since there was no sharp distinction from today to tomorrow in these divisions.

But still, at the turn of neighboring eras and periods, significant geological transformations predominantly took place: processes of mountain formation, redistribution of seas, climate change etc.

Each subsection was, of course, characterized by its unique flora and fauna.

, And You can read it in the same section.

Thus, these are the main eras of the Earth on which all scientists rely 🙂

We present to your attention an article about the classical understanding of the development of our planet Earth, written in a non-boring way, understandable and not too long..... If any of the older people have forgotten, it will be interesting to read, well, for those who are younger, and even for an abstract, it’s generally excellent material .

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

The gas and dust cloud transformed over time into solar system. And after the star appeared, the planets appeared. One of them was our native Earth. This 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.

The entire history of the Earth is divided into two huge stages.

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 approximately 540 million years ago. This is the time when living multicellular organisms spread across 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 stages are called eons. Each eon has its own eonothema. The latter represents a certain stage of the geological development of the planet, which is radically 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 eons in total. Each of them, in turn, is divided into eras of the Earth’s development, and those are divided into periods. From this it is clear that there is a strict gradation of large time intervals, and the geological development of the planet is taken as the basis.

Katarhey

The oldest eon is called Katarchean. 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. During the times of the Catarchaeus there was neither earth's crust, no core. The planet was a cold cosmic body. The temperature in its depths corresponded to the melting point of the substance. On top, 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 or oxygen.

Archaea

The second eon is called Archean. 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:

Eoarchaean
paleoarchean
mesoarchaean
neoarchaean

Eoarchaean(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. Comets could have brought it in large quantities. 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 this era of Earth's development, the first supercontinent of Vaalbara began to form.

Paleoarchaean(3.6–3.2 billion years) lasted 400 million years. During this era, the formation of the solid core of the Earth was completed. A strong magnetic field appeared. His tension was half the current one. Consequently, the surface of the planet received protection from the solar wind. This period also saw primitive forms of life in the form of bacteria. Their remains, which are 3.46 billion years old, were discovered 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. The most remarkable thing about it was the existence of cyanobacteria. They are capable of photosynthesis and release oxygen. The formation of the supercontinent has completed. By the end of the era it had split. There was also a huge asteroid impact. Its crater still exists in Greenland.

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

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

Proterozoic

The Proterozoic is divided into 3 eras. The first one is called Paleoproterozoic(2.5–1.6 billion years). It lasted 900 million years. This huge time interval is divided into 4 periods:

siderian (2.5–2.3 billion years)
Rhyasian (2.3–2.05 billion years)
orosirium (2.05–1.8 billion years)
statherians (1.8–1.6 billion years)

Siderius notable in the first place oxygen catastrophe. It happened 2.4 billion years ago. Characterized by a dramatic change in the Earth's atmosphere. Free oxygen appeared in it in huge quantities. Before 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, which proliferated on Earth 2.7 billion years ago. Before this, archaebacteria dominated. They did not produce oxygen during photosynthesis. In addition, oxygen was initially consumed in the oxidation of rocks. It accumulated in large quantities only in biocenoses or bacterial mats.

Eventually, a moment came when the surface of the planet became oxidized. And the cyanobacteria continued to release oxygen. And it began to accumulate in the atmosphere. The process 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 shrouded 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 Huronian glaciation, which lasted 300 million years. It began in Sideria, and ended at the end of Riasia 2 billion years ago. The next period of orosiria notable for its intense 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 located in Canada. Its diameter is 250 km.

Last staterian period notable for the formation of the supercontinent Columbia. It includes 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 of 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)
sthenia (1.2–1 billion years).

During such an era of the Earth's development as potassium, the supercontinent Columbia broke up. And during the Exatian era, 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 Stenium. It arose 1.1 billion years ago and disintegrated 750 million years ago. Thus, by the end of the Mesoproterozoic there was 1 supercontinent and 1 ocean on Earth, called Mirovia.

The last era of the Proterozoic is called Neoproterozoic(1 billion–540 million years). It includes 3 periods:

Thonium (1 billion–850 million years)
Cryogenian (850–635 million years)
Ediacaran (635–540 million years)

During the Thonian era, the supercontinent Rodinia began to disintegrate. This process ended in cryogeny, and the supercontinent Pannotia began to form from the 8 separate pieces of land that formed. Cryogeny is also characterized by complete glaciation of the planet (Snowball Earth). The ice reached the equator, and after it retreated, the process of evolution of multicellular organisms sharply accelerated. Last period 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 began - the Phanerozoic. There are 3 very important eras of the Earth. The first one is called Paleozoic(540–252 million years). It lasted 288 million years. 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 million years)
Permian (299–252 million years)

Cambrian considered to be the lifespan of trilobites. These are marine animals similar to crustaceans. Along with them, jellyfish, sponges and worms lived in the seas. Such an 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. Naturally, they were not preserved. Therefore, complex multicellular organisms of more ancient eras cannot be detected.

The Paleozoic is notable for the rapid expansion of organisms with hard skeletons. From vertebrates, fish, reptiles and amphibians appeared. The plant world was initially dominated by algae. During Silurian plants began to colonize the land. At the beginning Devonian The swampy shores are overgrown with primitive 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 colonize land during the Silurian period

Scorpions and spiders appeared. The dragonfly Meganeura was a real giant. 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, a wide variety of vegetation rapidly developed on the shores of 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 during 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 from Gondwana arose South America, Africa, Australia and Antarctica.

On Permian there were frequent climate changes. Dry times alternated with wet ones. At this time, lush vegetation appeared on the banks. Typical plants were cordaites, calamites, tree and seed ferns. Mesosaur 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 firmly and densely settled on the blue planet.

The following eras of the Earth's development are of particular interest to scientists. 252 million years ago came Mesozoic. It lasted 186 million years and ended 66 million years ago. Consisted of 3 periods:

Triassic (252–201 million years)
Jurassic (201–145 million years)
Cretaceous (145–66 million years)

The boundary between the Permian and Triassic periods is characterized by mass extinction of animals. 96% of marine species and 70% of terrestrial vertebrates died. The biosphere was dealt a very strong blow, 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 was the collapse of Pangea. The single supercontinent, as already mentioned, was divided into 2 continents, and then broke up into the continents that we know now. The Indian subcontinent also broke away. Subsequently, it connected with the Asian plate, but the collision was so severe that the Himalayas emerged.

This is what nature was like in the early Cretaceous period

The Mesozoic is notable for being considered the warmest period of the Phanerozoic eon.. It's time 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 across the planet. At the equator, the average annual temperature was 25-30° Celsius. The circumpolar 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 climate. It was at this time that the equatorial climate zone was formed.

In the animal world, mammals arose from the subclass of reptiles. This was due to the improvement of the nervous system and brain. The limbs moved from the sides under the body, and the reproductive organs became more advanced. They ensured the development of the embryo in the mother's body, followed by feeding it with milk. Hair 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 considered 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:

Paleogene (66–23 million years)
Neogene (23–2.6 million years)
modern Anthropocene or Quaternary period, which began 2.6 million years ago.

There are 2 main events observed in the Cenozoic. The mass extinction of dinosaurs 65 million years ago and the general cooling of the planet. The death of the 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. As a result, a crater was formed Chicxulub with a diameter of 180 km. It is located on the Yucatan Peninsula in Central America.

Surface of the Earth 65 million years ago

After the fall, there was an explosion of enormous force. Dust rose into the atmosphere and blocked 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 became extinct. 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 terrestrial animals has increased significantly compared to the Paleozoic. They became much more advanced, and mammals took a dominant position on the planet. Higher angiosperms appeared in the plant world. This is the presence of a flower and an ovule. Cereal crops also appeared.

The most important thing in the last era is anthropogen or quaternary period, which began 2.6 million years ago. It consists of 2 eras: 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 species of animals that became extinct at the end of the era lived on Earth. 300 thousand years ago, man appeared on the blue planet. It is believed that the first Cro-Magnons chose for themselves eastern regions Africa. At the same time, Neanderthals lived on the Iberian Peninsula.

Notable for the Pleistocene and Ice Ages. For as long as 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. During cold times, glaciers advanced on the continents, and retreated during interglacial periods. At the same time, the level of the World Ocean rose. About 12 thousand years ago, already in the Holocene, the next ice age ended. The climate became warm and humid. Thanks to this, humanity spread throughout the planet.

The Holocene is an interglacial. It has been going on for 12 thousand years. Over the past 7 thousand years, human civilization has developed. The world has changed in many ways. Flora and fauna have undergone significant transformations thanks to human activity. Nowadays, many animal species are on the verge of extinction. Man has long considered himself the ruler of the world, but the era of the Earth has not gone away. Time continues its steady course, and the blue planet conscientiously revolves around the Sun. In a word, life goes on, but the future will show what will happen next.

The Cretaceous period is a geological period, the last period of the Mesozoic era. Began 145 million years ago and ended 65 million years ago. The Cretaceous period lasted about 80 million years. In the Cretaceous period, the first angiosperms - flowering plants - appeared. This resulted in an increase in the diversity of insects that became flower pollinators. The evolution of the plant world gave impetus to the rapid development of the animal world, including dinosaurs. The diversity of dinosaur species reached its peak during the Cretaceous period. Cretaceous tectonics: Continental movement continued during the Cretaceous period. Laurasia and Gondwana were falling apart. Africa, India and Australia also began to diverge in different directions, and giant islands eventually formed south of the equator. South America and Africa were moving away from each other, and Atlantic Ocean became wider and wider. There were no obvious catastrophes during the Cretaceous period, so the process of evolution proceeded naturally. The earth took on shapes very close to those known to us. Cretaceous climate: The climate has changed compared to the Jurassic period. Due to the changing position of the continents, the change of seasons became more and more noticeable. Snow began to fall at the poles, although there were no such ice caps on Earth as there are now. The climate varied on different continents. This caused differences in the development of flora and fauna in different parts of the world. Flora of the Cretaceous Period: The flora of the Cretaceous period was rich and varied. In addition to the plant species carried over from the Jurassic period, a new, revolutionary branch of flowering plants appears. Flowering plants Having concluded an “alliance” with insects, they had advantages over their predecessors. Thanks to this partnership, flowering plants spread much faster. Gradually populating the land, new groups of plants began to form vast forests. There, a wide variety of leaves and other edible vegetation were available to land animals. Thanks to the appearance of flowering plants during the Cretaceous period, the amount of plant biomass increased. The reverse process took place at sea. This was again facilitated by the development of flowering plants. Dense roots prevented soil erosion and therefore less minerals entered the sea. The amount of phytoplankton has decreased. Cretaceous fauna: Insects: The growth of flowering plants during the Cretaceous period contributed to an increase in the species of nectar-feeding and pollen-dispersing insects. It was during the Cretaceous period. Insects have appeared whose life is completely dependent on flowering plants. These are bees and butterflies. Insects collected pollen and transported it to its destination. The brightly colored petals and attractive aroma of flowers became a bait for insects. In turn, the sweet, sugary nectar, and the pollen itself, supplied the insects with all the nutrients they needed. The Cretaceous period marked the beginning of an era of close interaction between plants and insects.

Dinosaurs: A variety of dinosaurs reigned among land animals. During the Cretaceous period, the diversity of dinosaur species was especially great. The development of the plant world and the increase in plant biomass gave impetus to the emergence of new species of herbivorous dinosaurs. Of the lizard-hipped dinosaurs, the most famous of which was Tyrannosaurus, Tarbosaurus, Spinosaurus, Deinonychus and others were common. The diversity of ornithischian dinosaurs was particularly high during the Cretaceous period. Widely known in the Jurassic period, stegosaurs will disappear from the face of the planet. Their place will be taken by such famous herbivorous dinosaurs as iguanodons, triceratops, ankylosaurs, pachycephalosaurs and many other species.

All the dinosaurs of the Cretaceous period...

Dinosaurs - the end of an era Flora and fauna are constantly evolving. Some species replace others. Some species are destined to dominate, while others modestly survive on the outskirts of the universe. But periodically, events occur that give evolution a chance to experiment with species and bring new ones into the arena that have shown themselves to be the best. In order to talk about how the time of dinosaurs ended, we will look at the end of the Cretaceous period. At the end of the Cretaceous period, another great extinction occurred. 65 million years ago, evolution received another opportunity for its experiments. For reasons we don't yet know for sure, the dinosaurs plesiosaurs and pterosaurs became extinct. Dinosaurs were just part of another great extinction event. Dinosaurs went extinct at the end of the Cretaceous period, about 65 million years ago. The extinction process was not rapid. It took about 5 million years, since the 70 million year old layers contain many dinosaur remains. By geological standards, this is a short period, but still the extinction was not instantaneous. The extinction of the dinosaurs was only part of the extinction that took place at the end of the Cretaceous period: along with the dinosaurs, marine reptiles (mosasaurs and plesiosaurs) and flying dinosaurs, many mollusks, including ammonites, belemnites and many small algae, became extinct. . However, most plants and animals survived this period. For example, land reptiles such as snakes, turtles, lizards and aquatic reptiles such as crocodiles have not become extinct. The closest relatives of ammonites, the nautiluses, also survived, not to mention birds, the first mammals, corals and land plants. In addition, some dinosaurs (triceratops, theropods, etc.) remained in western North America and India for several million years at the beginning of the Paleogene, after their extinction in other places.

The most popular versions of the extinction of dinosaurs are as follows. Astrophysical: 1. Asteroid fall The most common version at the moment. It is assumed that the impact of this asteroid may be the Chicxulub crater on the Yucatan Peninsula in Mexico. The version is very popular, perhaps because of its entertainment value. 2. A supernova explosion or a nearby gamma-ray burst. 3. Collision of the Earth with a comet. Geophysical and climatic: 1. Changes in average annual and seasonal temperatures, despite the fact that large dinosaurs depend on the external temperature, requiring a stable warm climate. 2. A sharp jump in the Earth's magnetic field. 3. Excess oxygen in the Earth's atmosphere. 4. Sharp cooling of the ocean. 5. Changes in the composition of sea water. 6. Increased volcanic activity. 7. Change in the gravitational attraction of the Earth. Evolutionary-biological: 1. Widespread spread of an infectious disease among one or many species of dinosaurs in a certain area, significantly exceeding the incidence rate usually recorded in this area. In other words, it's an epidemic. 2. Dinosaurs were unable to adapt to the change in vegetation type and were poisoned by alkaloids contained in the emerging flowering plants. 3. Dinosaurs were the first to be exterminated carnivorous mammals, destroying clutches of eggs and young. All of the above hypotheses are popular, mainly among non-specialists. Most likely because of its picturesqueness. Professional paleontologists have a sharply negative attitude towards this kind of hypotheses. None of them can fully explain the entire complex of phenomena associated with the extinction of dinosaurs and other species at the end of the Cretaceous period. As a result of what has been described, the main problems of the listed versions are as follows: - Some hypotheses are unacceptable simply because they do not correspond to the facts or do not have factual evidence. Thus, no traces of rapid changes in the magnetic field were found (drift magnetic poles occurs quite slowly and is precisely tracked by geological traces), fluctuations in ocean temperature or widespread catastrophic volcanism. - All impact hypotheses, including astronomical ones, do not explain the selectivity of extinction and do not correspond to the duration of its period. In addition, the degree of danger of the consequences of the destruction of cosmic bodies for the biosphere is exaggerated: traces of repeated collisions of the Earth with large asteroids have been reliably recorded, but during the periods when they occurred, no significant changes in the biosphere were recorded. There were local disasters at the crash sites, which the rest of the living world practically did not notice. Opinion of paleontologists: When studying the causes of the extinction of dinosaurs, it is necessary to note some important features: - The extinction can only be called “rapid” by geological standards; in reality, it took several million years. - It is not entirely correct to talk about the rapid extinction of dinosaurs. In any group of living beings, an evolutionary process is constantly going on - the formation of new species and the extinction of previously existing ones. These processes occur simultaneously, and if the rates of extinction and formation of new species are equal, the group exists. And there is no reason to talk about extinction. From this point of view, during the period of the “great extinction,” the rate of dinosaur extinction itself, that is, the disappearance of previously existing species, does not exceed the rate of extinction in previous periods. But, at the end of the Cretaceous period, something went wrong and new species of dinosaurs did not replace the extinct species, as a result of which dinosaurs became completely extinct. Modern paleontology is dominated by the biosphere version of the “great extinction,” including the extinction of the dinosaurs. According to it, the main initial factors that predetermined the extinction of dinosaurs were: 1. The appearance of flowering plants; 2. Gradual climate change caused by continental drift. The sequence of events leading to extinction appears to be as follows: - Flowering plants with more developed root system and better using soil fertility, quickly replaced other types of vegetation everywhere. At the same time, insects specialized in feeding on flowering plants appeared, and insects “attached” to previously existing types of vegetation began to die out. - Flowering plants form turf, which is the best natural erosion suppressor. As a result of their spread, the erosion of the land surface and, accordingly, the flow of nutrients into the oceans have decreased. The “depletion” of the ocean in food led to the death of a significant part of the algae, which were the main primary producer of biomass in the ocean. Along the chain, this led to a complete disruption of the entire marine ecosystem and became the cause of mass extinctions at sea. The same extinction also affected large flying dinosaurs, which, according to existing ideas, were closely associated with the sea. After extinction at sea, pterosaurs' food resources became scarce. Some of the large marine reptiles, in addition, could not withstand competition with the modern type of sharks that appeared at this time. - On land, animals actively adapted to feeding on green matter (by the way, herbivorous dinosaurs too). In the small size class, small mammals like rats appeared. Their appearance led to the emergence of corresponding predators, which also became mammals. Small-sized mammalian predators were not dangerous for adult dinosaurs, but they fed on their eggs and young, creating additional difficulties for dinosaurs in reproduction. At the same time, protecting the offspring is practically impossible for a dinosaur due to the too large difference in the sizes of adults and young. As a result of the movement of continents at the end of the Cretaceous period, the Earth acquired almost familiar shapes. The air and sea currents, which led to some cooling over a significant part of the land and increased temperature changes. At the poles, the change of seasons began to be felt. And although the temperature did not drop to -70°C as it does now, it dropped to 0°C, and maybe a little lower. Inertial homeothermy, which provided dinosaurs with an evolutionary advantage in previous periods, no longer had an effect under such conditions. As a result of all these reasons, unfavorable conditions were created for dinosaurs, which led to the cessation of the emergence of new species. The developed species of dinosaurs existed for some time, but gradually died out completely. Apparently, there was no severe direct competition between dinosaurs and mammals; they occupied different size classes, existing in parallel. Only after the disappearance of dinosaurs did mammals take over the vacated ecological niche, and even then not immediately. Interestingly, the appearance of the first dinosaurs - archosaurs, at one time was marked by the massive (but not complete) extinction of therapsids (beast-like reptiles), the highest forms of which were essentially primitive oviparous mammals...

Billions of years ago, our Earth was a bare, lifeless planet. And then life appeared on its surface - those first, most primitive forms of living beings, the development of which led to the endless diversity of the nature around us. How did this development take place? How did animals and plants appear on Earth, how did they change? This book will answer some of these questions. Its author, the outstanding Soviet scientist Academician V.L. Komarov, described in it the history of the Earth's flora - from the simplest unicellular bacteria to modern highly developed flowering plants. This long haul development, the author draws in close connection with general history Earth, with its changes natural conditions, relief, climate. The book is written popularly, is easy to read and will be of great benefit to the widest range of readers who have basic knowledge of the field of biology in the scope of a school course.

(more ancient systems of sedimentary strata are placed below, those closer to modern ones are placed above)

Eras	Periods	Dominant group of plants and animals	Length of periods in millions of years
Cenozoic	Quaternary	Domination modern species and creation of cultivated plants and animals	1
	Tertiary	Dominance and diversity of angiosperms (flowering) plants. The gradual development of modern flora, the establishment of modern plant species. Diversity of mammals, birds, insects	69
Mesozoic	Chalky	The appearance and development of angiosperms (flowering) plants, the establishment of modern plant genera. Extinction of cycads and ginkgos. The appearance of red calcareous algae. Further development reptiles, birds and insects and mammals	40
	Jurassic	Development and wide distribution of gymnosperms - cycads, ginkgos and conifers. The appearance of diatoms. Disappearance of pteridosperms Reptiles. Primary birds. Mammals	40
	Triassic	Development of cycads, ginkgos and conifers. Development of ferns. Extinction of Cordaites. Development of reptiles. The first mammals are marsupials	35
Paleozoic	Permian	Extinction of tree-like moss and horsetails; emergence of modern families of pteridophytes. Appearance of conifers (Bayera and Walchia). Distribution of glossopteria flora. Reptiles	40
	Coal	Development of pteridophytes (tree mosses, horsetails, ferns). Pteridosperms and cordaites. The rise of amphibians. Towards the end of the period - the appearance of insects	50
	Devonian	Psidophytes and primary fern-like plants. The first gymnosperms are pteridosperms (fern-like gymnosperms). The emergence of mushrooms. By the end of the period - the extinction of the psilophyte flora. Various fish. Lungfish	35
	Silurian	The first land plants are psilophytes. A variety of marine invertebrates. Fish	35
	Cambrian	The first signs of stem plants. Predominance of trilobites. Algae and bacteria	80
Proterozoic		Bacteria and algae. Protozoa animals	About 700
Archean		Limestones, m.b. bacterial origin

Until now, only geological and climatic forces were at work in nature. As we have seen, they have always had a strong influence on the vegetation and contributed to its greater and greater diversity. Now a completely new factor has appeared: man.

Originating in the Tertiary period, according to various estimates, 600,000 - 1,000,000 years before our time, in ape-like forms, it met the Ice Age still unarmed. But in many places it was impossible to escape from the glacier; the cold drove man into the caves, which became his first home, and forced him to invent devices for maintaining fire. From this moment, man becomes an industrial being and, increasingly intensifying his activity, begins to influence nature more powerfully than any other living creature. He clears forests, raises virgin soil, breaks through canals, blows up and digs up entire mountains, and generally changes the face of the Earth at his own discretion.

* * *

In relation to vegetation, man destroys forest flora, destroys steppe plants and many others and creates in their place his own special world, a world of cultivated plants, which would never have existed if not for man. The contemporary period of development of earthly vegetation is precisely characterized by the replacement by man of the flora inherited from previous times by cultivated vegetation.

We have seen that the conditions of plant life on Earth first put forward, as the pioneers of the primary settlement of the earth's crust, a group of bacteria known under the general name chemotrophic, i.e., those whose nutrition is limited to a small number of clearly defined, chemical reactions and does not require previously formed organic matter.

The age of bacteria was subsequently replaced by the age of algae, which in the waters of the ancient oceans reached a significant variety of shapes and colors.

The age of algae gave way on the primary continents to the age of psilophytes, which gave rise to vegetation reminiscent in its general appearance and size of modern thickets of large mosses.

The age of psilophytes gave way to the age of fern-like plants, which already formed extensive forests on marshy soils. This vegetation greatly contributed to the fact that both the composition of the air and the accumulation of mass of nutrients made possible the emergence of the first land vertebrates. At the same time, the main masses of coal accumulated.

The age of ferns gave way to the age of cone-bearing plants. For the first time, the surface of the continents acquired a modern appearance in some places and the possibility of the existence of higher animals became even closer.

The age of cone-bearing plants was gradually replaced by the age of flowering plants, when, one after another, all the plants that exist today were formed.

It must be said that the onset of a new century or period never completely destroyed the old plant world. Always a part of the past population of the Earth was preserved and continued to exist along with the new world. Thus, with the appearance of higher vegetation, bacteria not only did not disappear, but also found new sources of existence for themselves in the soil and in the organic matter so generously created by higher plants. Algae, once developed, continue to grow and improve along with higher plants. Moreover, they are not competitors to them, since some inhabit coastal sea areas, while others mainly live on land.

Finally, the coniferous forests of our time continue to exist along with deciduous ones, and their shade provides shelter for fern-like plants, since this legacy of the foggy and humid Carboniferous period is afraid of open habitats where the sun’s rays harm it, and seeks shade.

Thus the history of the earth's crust led to the creation of a rich and varied world of plants, beginning its work from the materials provided by the inorganic world, and ending with the creation of what surrounds us and provides us with everything we need for life.

“Zoology and botany remain still fact-gathering sciences until paleontology - Cuvier - joins in, and soon afterwards the discovery of the cell and the development of organic chemistry. Thanks to this, comparative morphology and comparative physiology became possible, and since then both have become genuine sciences."

F. Engels

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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 began to take effect. The duration of this era is approximately 2 billion years, i.e. it corresponds to all other eras combined. The Archean era appears to have been characterized by catastrophic and widespread volcanic activity, as well as deep uplifts that culminated 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 life of those times still remained. In Archeozoic rocks, graphite or pure carbon is found everywhere in scattered form, which probably represents 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 the case), then in the Archean there was probably a lot of this living matter, since there is more carbon in 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 large amounts of sediment 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 have been found in Proterozoic rocks, which, however, indicate not only the existence of life in this era, but also that evolutionary development had advanced far ahead by the end of the Proterozoic. Sponge spicules, remains of jellyfish, fungi, algae, brachiopods, arthropods, etc. were 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. Over 370 million years of the Paleozoic era, representatives of all types and classes of animals appeared, with the exception of birds and mammals. Because different types animals existed only for certain periods of time, their fossil remains allow geologists to compare sediments of the same age found in different places.

Cambrian period [show] .
Cambrian period- the most ancient department of the Paleozoic era; is represented by rocks replete with fossils, so that the appearance of the Earth at this time can be reconstructed quite accurately. 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 Archean.
All modern types 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 arachnid-like forms; some of their descendants have survived, almost unchanged, to this day (horseshoe crabs). The seabed was covered with solitary sponges, corals, stalked echinoderms, gastropods and bivalves, primitive cephalopods, brachiopods and trilobites.
Brachiopods, sessile animals that have bivalve shells and feed 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 two-branched limbs; one of them was used for walking or swimming and had a gill on it. Most trilobites were 5-7.5 cm in length, 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 characterized mainly 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 with more highly organized ones. Probably, the already existing forms reached such a degree of adaptation to environmental conditions that they acquired a significant advantage over any new, unadapted types.
Ordovician period [show] .
During the Cambrian period, the continents began to gradually submerge in water, and in the Ordovician period this subsidence reached its maximum, so that much of the present landmass was covered by shallow seas. These seas were inhabited by huge cephalopods - 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 were apparently very warm, since corals, which live only in warm waters, spread at this time as far as Lake Ontario and Greenland.
The first remains of vertebrates were found in Ordovician deposits. These small animals, called scutes, were bottom-dwelling forms, lacking jaws and paired fins (Fig. 1.). Their shell 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 as protection from giant predatory aquatic scorpions called eurypterids, which also lived in fresh water.
Silurian [show] .
Two major events occurred in the Silurian period biological significance: Land plants developed and air-breathing animals appeared.
The first land plants were apparently more similar to ferns than to mosses; Ferns were also the dominant plants in the subsequent Devonian and lower Carboniferous periods.
The first air-breathing land animals were arachnids, somewhat reminiscent of modern scorpions.
Continents that had been low-lying in 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 fish gave rise to many different fish, so that this period is often called the “time of the fish.”
Jaws and paired fins first evolved in armored sharks (Placodermi), which were small, shell-covered 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, true sharks appeared in fresh waters, which showed a tendency to move to the ocean and lose their bulky bony shell.
The ancestors of bony fishes also arose in Devonian freshwater streams; by the middle of this period, they developed 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 lungfishes have survived to this day, and the ray-finned fishes, having undergone 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 fishes (Teleostei).
Lobe-finned fish, which were the ancestors of land vertebrates, almost became extinct by the end of the Paleozoic and, as previously believed, completely disappeared at the end of the Mesozoic. However, in 1939 and 1952. off the east coast South Africa Live representatives of lobe-fins, about 1.5 m long, were caught.
The upper Devonian was marked by the appearance of the first land vertebrates - amphibians called stegocephalians (meaning "covered-headed"). 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 rather than fins.
The Devonian is the first period characterized by real forests. During this period, ferns, club mosses, pteridophytes and primitive gymnosperms - the so-called "seed ferns" - flourished. It is believed that insects and millipedes arose in late Devonian times.
Carboniferous period [show] .
At this time, large swamp 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 pteridophytes, common ferns, seed ferns and broad-leaved evergreens.

The first reptiles, called whole-skulled and similar to the amphibians that preceded them, appeared in the second half of the Carboniferous period, reached their peak in the Permian - the last period of the Paleozoic - and died out at the beginning of the Mesozoic era. It is not clear whether the most primitive reptile known to us, Seymouria (named after the city in Texas near which its fossil remains were found), was an amphibian ready to turn into a reptile, or a reptile that had just crossed 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 shell, in water, and reptiles lay their eggs, covered with a durable shell, on the ground. Since the eggs of Seymouria have not been preserved, we may never be able to decide to what class this animal should be placed.
Seymouria was a large, slow-moving, lizard-like form. Its short, stump-like legs extended away from its body in a horizontal direction, like a salamander's, instead of being tightly packed and going straight down, forming 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. The continents have risen on everything globe, so that the shallow seas that covered the area from Nebraska to Texas dried up, leaving behind a saline desert. At the end of the Permian, widespread folding occurred, known as the Hercynian orogeny, during which a large mountain range rose from Nova Scotia to Alabama. This range was originally higher than the modern Rocky Mountains. At the same time, other mountain ranges were forming in Europe.
Huge ice sheets spreading from the Antarctic covered most of southern hemisphere, extending in Africa and Brazil almost to the equator.
North America was one of the few areas not subject to glaciation at this time, but even here the climate became significantly colder and drier than it had been during most of the Paleozoic era. Many Paleozoic organisms apparently could not adapt to climate change and became extinct during the Hercynian orogeny. Due to the cooling of water and the reduction of space suitable for life as a result of the drying out of shallow seas, even many marine forms became extinct.
From primitive whole-skulled animals, during the Late Carboniferous and Early Permian times, that group of reptiles developed, from which mammals are believed to have descended in a direct line. These were pelycosaurs - predatory reptiles with a more slender and lizard-like body than those of whole skulls.
In the Late Permian time, another group of reptiles, the therapsids, developed, probably from pelycosaurs, and had several more characteristics of mammals. One of the representatives of this group, Cynognathus (the “dog-jawed” reptile), 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 uniform, as is typical of reptiles, were 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 a reptile. However, if we had more complete data, it might 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 approximately 230 million years ago and lasted about 167 million years, is divided into three periods:

Triassic
Jurassic
chalky

During the Triassic and Jurassic periods, most of the continental areas 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 Arizona's famous Stone Forest have been around since the Triassic period.

During the Cretaceous period, the Gulf of Mexico expanded and flooded Texas and New Mexico, and in general the sea gradually advanced onto the continents. In addition, extensive swamps have developed in an area stretching from Colorado to British Columbia. At the end of the Cretaceous period, the interior of the North American continent experienced further subsidence, so that the waters of the Gulf of Mexico basin connected with the waters of the Arctic basin and divided this continent into two parts. The Cretaceous period ended with a large uplift called the Alpine orogeny, during which the Rocky Mountains, Alps, Himalayas and Andes were created and which caused active volcanic activity in western North America.

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

The most primitive branch includes, in addition to the ancient whole-skulls, turtles that arose in the Permian. Turtles have developed the most complex shell (among terrestrial animals); it consists of plates of epidermal origin fused with the underlying ribs and sternum. With this protective adaptation, both sea and land turtles have survived from pre-dinosaur times with few structural changes. The legs of turtles, extending from the body in a horizontal direction, which complicates and slows down movement, and their skulls, which do not have holes behind the eye sockets, were inherited from ancient whole-skulls without changes.

The second group of reptiles, which comes with relatively few changes from the ancestral whole-skulled ones, are lizards, the most numerous among living reptiles, as well as snakes. Lizards for the most part have retained a primitive type of movement using horizontally diverging legs, although many of them can run quickly. In most cases they are small, but the Indian monitor reaches 3.6 m in length, and some fossil forms are 7.5 m in length. Mosasaurs of the Cretaceous period 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 significant 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.

A representative of an ancient branch that somehow managed to survive to this day in New Zealand is the hatteria (Shpenodon punctatum). It shares several features with its cotylosaurian ancestors; one such sign is the presence of a third eye at the top of the skull.

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

Early archosaurs evolved into many different specialized forms, with some continuing to walk on two legs and others returning 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 a robin, as well as the largest animal ever to fly, Pteranodon, with a wingspan of 8 m.

There were two types of flying reptiles; some had a long tail equipped with a steering 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, like bats, they rested in a suspended state, clinging to some support.

Of all the branches of reptiles, the most famous are dinosaurs, which translated means “terrible lizards.” They were divided into two main types: ornithischians and saurians.

Saurischia (lizard-mouthed) first appeared in the Triassic and continued to exist until the Cretaceous. Early lizards were fast, predatory, bipedal, rooster-sized forms that likely preyed on lizards and the primitive mammals that had already emerged. During the Jurassic and Cretaceous periods, this group showed a tendency to increase in size, reaching its highest expression in the giant Cretaceous predator Tyrannosaurus. Other Saurischia, which appeared in Late Triassic times, switched to a plant diet, 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 ever lived include brontosaurus, 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 walked on their hind legs, most walked 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 a duck's (hence the name "duck-billed" dinosaurs). This type is characterized by webbed feet. Other species developed large armor plates that protected them from predatory lizards. Ankylosaurus, which is called a “tank reptile,” had a wide, flat body covered with bony plates and large spines protruding from its sides.

Finally, some Cretaceous ornithischians developed bony plates around the head and neck. One of them, Triceratops, had two horns over the eyes and a third over the nasal area - all up to almost 1 m long.

Two other groups of Mesozoic reptiles that differed both from each other and from dinosaurs were the marine plesiosaurs and ichthyosaurs. The first were characterized by an extremely long neck, accounting for 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. They often reached 13-14 m in length.

Ichthyosaurs (fish lizards) were similar in appearance to fish or whales, with a short neck, a large dorsal fin and a shark-like tail. They swam using rapid movements of their tails, 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 adult individuals were too specialized and could not go onto land to lay eggs, and reptile eggs drown in water. The discovery of baby skeletons inside the abdominal cavity of adult fossils supports this theory.

At the end of the Cretaceous, many reptiles became extinct. 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 cumbersome 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 influence of a number of factors or of a single factor.

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

During the Mesozoic, the number and diversity of gastropods and bivalves increased. Sea urchins reached highest point of its development.

Mammals arose in the Triassic, and bony fish and birds appeared in the Jurassic.

Most modern insect orders appeared in the early Mesozoic.

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

From Jurassic times, magnificent prints 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, armed with jaw teeth and a long, reptilian tail covered with feathers.

Fossils of two other birds were found in the Cretaceous deposits - Hesperornis and Ichthyornis. 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 equally rightly 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 mountain formation (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 divided into five eras: Paleocene, Eocene, Oligocene, Miocene and Pliocene. The rocky mountains, formed at the beginning of the Tertiary period, were already heavily eroded by the Oligocene time, as a result of which the North American continent acquired a gently undulating topography.
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 today, so palms spread as far north as Wyoming.
The uplift, which began in the Miocene, continued into the Pliocene and, combined with the glaciations of 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, was almost completed in the short time of the Pleistocene and modern eras.
The oldest fossil remains of true mammals date back to the Late Triassic, and in Jurassic times there were already four orders of mammals, all of them the size of a rat or a small dog.
The oldest mammals (monotremes) were oviparous animals, and their only representatives that have survived to this day are the platypus and the spiny echidna living in Australia. Both of these forms have fur and nurse their young with milk, but they also lay eggs, like turtles. The ancestral oviparous mammals must, of course, have been distinct from the specialized platypus and echidna, but the fossil record of these ancient forms is incomplete. The only reason living monotremes could survive so long is because they lived in Australia, where until recently there were no placental mammals, so they had nothing to compete with.
In the Jurassic and Cretaceous, most mammals were already highly enough organized to produce live young, although in the most primitive of them - marsupials - the young are born underdeveloped and must remain for several months in a pouch on the mother's stomach, where the nipples are located. Australian marsupials, like monotremes, did not encounter 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 various forms, externally resembling some placentals. There are marsupial mice, shrews, cats, moles, bears and one species of wolf, as well as a number of forms that have no placental parallels, such as kangaroos, wombats and wallabies.
During the Pleistocene, Australia was home to giant kangaroos and rhino-sized wombats. Opossums are more similar to the 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 Cretaceous sediments, show that it was a very small animal, like the living shrew. Some of these ancestral mammals retained an arboreal lifestyle and, through a series of intermediate forms, gave rise to primates - monkeys and humans. Others lived on or underground, and during the Paleocene, from them all other mammals living today evolved.
Primitive Paleocene mammals had conical reptilian teeth, five-fingered limbs, and a small brain. In addition, they were plantigrade, not digitigrade.
During the Tertiary period, the evolution of herbaceous plants that served as food and forests that sheltered animals was the most important factor influencing changes in the body structure of mammals. Along with the 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 the teeth and legs. When new, more adapted forms appeared, primitive mammals became extinct.
Although fossils of both marsupials and placentals were found in the Cretaceous deposits, the discovery of highly developed mammals in the early Tertiary deposits was quite unexpected. Whether they really arose at this time or existed before in mountainous areas and were simply not preserved in the form of fossils is not known.
In the Paleocene and Eocene, the first predators called creodonts evolved 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 pinnipeds of the sea - seals and walruses.

One of the most famous fossil predators is the saber-toothed tiger, which only recently became extinct during 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 victim like sabers.
Large herbivorous mammals, most of which have 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 the cow and the horse, despite the presence of hooves in both, are no more related to each other than each of them is to the tiger. The molars of ungulates are flattened and enlarged, which makes it easier to grind leaves and grass. Their legs became long and adapted to the fast running needed to escape 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 similar to primitive predators, the creodonts, were primitive ungulates called Uintatherians. 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 fossil record of several evolutionary lineages 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-toed forms. The main direction of evolution in ungulates was towards an increase in overall body size and a decrease in the number of fingers. Ungulates early split into two groups, one of which is characterized by an even number of digits and includes cows, sheep, camels, deer, giraffe, pigs and hippos. Another group is characterized by an odd number of toes and includes horses, zebras, tapirs and rhinoceroses.
The development of elephants and their recently extinct relatives - mammoths and mastodons - can be traced back centuries to an Eocene ancestor that was the size of a pig and had no trunk. This primitive form, called Moeritherium, was close to the trunk, from which also branched such dissimilar forms as the hyrax (a small animal similar to the marmot, found in Africa and Asia) and the 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 edentates (anteaters, sloths and armadillos) - is less known.
Quaternary period (time of man). The Quaternary period, which covers the last 1-1.5 million years, is usually divided into two eras - Pleistocene and modern. The latter began approximately 11,000 years ago, with the retreat of the last glacier. The Pleistocene was characterized by four ice ages, separated by intervals when glaciers retreated. At the time of maximum expansion, ice sheets occupied almost 10 million square meters in North America. km, extending south all the way to the Ohio and Missouri rivers. The Great Lakes, which were plowed by moving glaciers, radically changed their shape 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 lakes as far as Duluth in the west and Buffalo in the east, its flow was more than 60 times greater than it is today. During the Pleistocene glaciations, such an amount of water was removed from the sea and converted into ice that the sea level dropped by 60-90 m. This caused the formation of land connections that served as settlement routes for many terrestrial organisms, between Siberia and Alaska in the Bering Strait region and between England and the European mainland.
Plants and animals of the Pleistocene era were similar to modern ones. It is sometimes difficult to distinguish Pleistocene deposits from Pliocene deposits, since the organisms they contain are similar to each other and to modern forms. During the Pleistocene, after the emergence of primitive humans, many mammals became extinct, including the saber-toothed tiger, mammoth, and giant ground sloth. The Pleistocene also saw the extinction of many plant species, especially forest ones, and the appearance of numerous herbaceous forms.
The fossil record leaves no doubt that living species are descended 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 yield good fossil remains, and intermediate forms that serve as links between different types animals were obviously forms without a skeleton, and no traces of them remained. For many evolutionary lines, in particular for vertebrates, the successive stages of development are well known. There are gaps in other lines that future paleontologists will have to fill.