Eras of earth development. History of the geological development of the earth Geological era is the time of the appearance of vegetation

The history of our planet still holds many mysteries. Scientists from various fields of natural science have contributed to the study of the development of life on Earth.

Our planet is believed to be about 4.54 billion years old. This entire time period is usually divided into two main stages: Phanerozoic and Precambrian. These stages are called eons or eonothema. Eons, in turn, are divided into several periods, each of which is distinguished by a set of changes that occurred in the geological, biological, and atmospheric state of the planet.

1. Precambrian, or cryptozoic is an eon (time period in the development of the Earth), covering about 3.8 billion years. That is, the Precambrian is the development of the planet from the moment of formation, the formation of the earth’s crust, the proto-ocean and the emergence of life on Earth. By the end of the Precambrian, highly organized organisms with a developed skeleton were already widespread on the planet.

The eon includes two more eonothems - catarchaean and archaean. The latter, in turn, includes 4 eras.

1. Katarhey- this is the time of the formation of the Earth, but there was no core or crust yet. The planet was still a cold cosmic body. Scientists suggest that during this period there was already water on Earth. The Catarchaean lasted about 600 million years.

2. Archaea covers a period of 1.5 billion years. During this period, there was no oxygen on Earth yet, and deposits of sulfur, iron, graphite, and nickel were being formed. The hydrosphere and atmosphere were a single vapor-gas shell that enveloped the globe in a dense cloud. The sun's rays practically did not penetrate through this curtain, so darkness reigned on the planet. 2.1 2.1. Eoarchaean- This is the first geological era, which lasted about 400 million years. The most important event of the Eoarchean was the formation of the hydrosphere. But there was still little water, the reservoirs existed separately from each other and did not yet merge into the world ocean. At the same time, the earth's crust becomes solid, although asteroids are still bombarding the earth. At the end of the Eoarchean, the first supercontinent in the history of the planet, Vaalbara, formed.

2.2 Paleoarchean- the next era, which also lasted approximately 400 million years. During this period, the Earth's core is formed and the magnetic field strength increases. A day on the planet lasted only 15 hours. But the oxygen content in the atmosphere increases due to the activity of emerging bacteria. Remains of these first forms of Paleoarchean life have been found in Western Australia.

2.3 Mesoarchean also lasted about 400 million years. During the Mesoarchean era, our planet was covered by a shallow ocean. The land areas were small volcanic islands. But already during this period, the formation of the lithosphere begins and the mechanism of plate tectonics starts. At the end of the Mesoarchean, the first ice age occurs, during which snow and ice first formed on Earth. Biological species are still represented by bacteria and microbial life forms.

2.4 Neoarchaean- the final era of the Archean eon, the duration of which is about 300 million years. Colonies of bacteria at this time form the first stromatolites (limestone deposits) on Earth. The most important event of the Neoarchean was the formation of oxygen photosynthesis.

II. Proterozoic- one of the longest time periods in the history of the Earth, which is usually divided into three eras. During the Proterozoic, the ozone layer appears for the first time, and the world ocean reaches almost its modern volume. And after the long Huronian glaciation, the first multicellular life forms appeared on Earth - mushrooms and sponges. The Proterozoic is usually divided into three eras, each of which contained several periods.

3.1 Paleo-Proterozoic- the first era of the Proterozoic, which began 2.5 billion years ago. At this time, the lithosphere is fully formed. But the previous forms of life practically died out due to an increase in oxygen content. This period was called the oxygen catastrophe. By the end of the era, the first eukaryotes appear on Earth.

3.2 Meso-Proterozoic lasted approximately 600 million years. The most important events of this era: the formation of continental masses, the formation of the supercontinent Rodinia and the evolution of sexual reproduction.

3.3 Neo-Proterozoic. During this era, Rodinia breaks up into approximately 8 parts, the superocean of Mirovia ceases to exist, and at the end of the era, the Earth is covered with ice almost to the equator. In the Neoproterozoic era, living organisms for the first time begin to acquire a hard shell, which will later serve as the basis of the skeleton.

III. Paleozoic- the first era of the Phanerozoic eon, which began approximately 541 million years ago and lasted about 289 million years. This is the era of the emergence of ancient life. The supercontinent Gondwana unites the southern continents, a little later the rest of the land joins it and Pangea appears. Climatic zones begin to form, and the flora and fauna are represented mainly by marine species. Only towards the end of the Paleozoic did land development begin and the first vertebrates appeared.

The Paleozoic era is conventionally divided into 6 periods.

1. Cambrian period lasted 56 million years. During this period, the main rocks are formed, and a mineral skeleton appears in living organisms. And the most important event of the Cambrian is the emergence of the first arthropods.

2. Ordovician period- the second period of the Paleozoic, which lasted 42 million years. This is the era of the formation of sedimentary rocks, phosphorites and oil shale. The organic world of the Ordovician is represented by marine invertebrates and blue-green algae.

3. Silurian period covers the next 24 million years. At this time, almost 60% of living organisms that existed before die out. But the first cartilaginous and bony fishes in the history of the planet appear. On land, the Silurian is marked by the appearance of vascular plants. Supercontinents are moving closer together and forming Laurasia. By the end of the period, ice melted, sea levels rose, and the climate became milder.

4. Devonian period is characterized by the rapid development of diverse life forms and the development of new ecological niches. The Devonian covers a time period of 60 million years. The first terrestrial vertebrates, spiders, and insects appear. Sushi animals develop lungs. Although, fish still predominate. The flora kingdom of this period is represented by propferns, horsetails, mosses and gosperms.

5. Carboniferous period often called carbon. At this time, Laurasia collides with Gondwana and a new supercontinent Pangea appears. A new ocean is also formed - Tethys. This is the time of the appearance of the first amphibians and reptiles.

6. Permian period- the last period of the Paleozoic, ending 252 million years ago. It is believed that at this time a large asteroid fell on Earth, which led to significant climate change and the extinction of almost 90% of all living organisms. Most of the land is covered with sand, and the most extensive deserts appear that have ever existed in the entire history of the development of the Earth.

IV. Mesozoic- the second era of the Phanerozoic eon, which lasted almost 186 million years. At this time, the continents acquired almost modern outlines. A warm climate contributes to the rapid development of life on Earth. Giant ferns disappear and are replaced by angiosperms. The Mesozoic is the era of dinosaurs and the appearance of the first mammals.

The Mesozoic era is divided into three periods: Triassic, Jurassic and Cretaceous.

1. Triassic period lasted just over 50 million years. At this time, Pangea begins to break apart, and the internal seas gradually become smaller and dry out. The climate is mild, the zones are not clearly defined. Almost half of the land's plants are disappearing as deserts spread. And in the kingdom of fauna the first warm-blooded and land reptiles appeared, which became the ancestors of dinosaurs and birds.

2. Jurassic covers a span of 56 million years. The Earth had a humid and warm climate. The land is covered with thickets of ferns, pines, palms, and cypresses. Dinosaurs reign on the planet, and numerous mammals were still distinguished by their small stature and thick hair.

3. Cretaceous period- the longest period of the Mesozoic, lasting almost 79 million years. The separation of the continents is almost ending, the Atlantic Ocean is significantly increasing in volume, and ice sheets are forming at the poles. An increase in the water mass of the oceans leads to the formation of a greenhouse effect. At the end of the Cretaceous period, a catastrophe occurs, the causes of which are still not clear. As a result, all dinosaurs and most species of reptiles and gymnosperms became extinct.

V. Cenozoic- this is the era of animals and homo sapiens, which began 66 million years ago. At this time, the continents acquired their modern shape, Antarctica occupied the south pole of the Earth, and the oceans continued to expand. Plants and animals that survived the disaster of the Cretaceous period found themselves in a completely new world. Unique communities of life forms began to form on each continent.

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

1. Paleogene period ended approximately 23 million years ago. At this time, a tropical climate reigned on Earth, Europe was hidden under evergreen tropical forests, only deciduous trees grew in the north of the continents. It was during the Paleogene period that mammals developed rapidly.

2. Neogene period covers the next 20 million years of the planet's development. Whales and bats appear. And, although saber-toothed tigers and mastodons still roam the earth, the fauna is increasingly acquiring modern features.

3. Quaternary period began more than 2.5 million years ago and continues to this day. Two major events characterize this time period: the Ice Age and the emergence of man. The Ice Age completely completed the formation of the climate, flora and fauna of the continents. And the appearance of man marked the beginning of civilization.

The course and direction of the process of the emergence of species in accordance with the basic principles of Charles Darwin’s theory of evolution are supported by data from various branches of biology, including data from the field of paleontology, which serve as material evidence, as 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 others changed little, and others died out. Based on the finds of fossil forms in the sediments of the earth's strata, it is possible to trace the true history of living nature. This is how paleontological series of the horse (V.O. Koralevsky), elephant, some birds, mollusks, etc. 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 places where paleontological remains occur 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 most ancient stage in the history of the Earth, when life arose in the waters of the primordial seas, which was originally presented precellular its forms and the first cellular organisms. Wasp analysis Dock rocks of this age show 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 and the sexual process arose, which 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 integration 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 deposits of this era only imprints of bacteria, algae, lower types of invertebrates and lower chordates. A major step in evolution was the appearance of organisms with bilateral symmetry of the body, differentiated into anterior and posterior sections, left and right sides, and a separation of the dorsal and ventral surfaces. The dorsal surface of the animals served as protection, and the ventral surface housed the mouth and food-grasping organs.

3. Paleozoic era. The flora and fauna reached great diversity, and 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-layered animals of that period were archaeocyaths, which formed reefs in ancient seas. They died out without leaving descendants. Only people lived on land bacteria And mushrooms.

During the Ordovician period, the climate was warm even in the Arctic. In the fresh and brackish waters of this period, planktonic species reached their peak development. seaweed, various corals from the phylum Coelenterata, there were representatives of almost all types invertebrates including trilobites, mollusks, echinoderms. Bacteria were widely represented. The first representatives of jawless vertebrates appear - Scutellaceae.

At the end of the Silurian period, due to mountain-building processes and a reduction in the area of ​​seas, some algae found themselves in new environmental conditions - in small reservoirs and on land. Many of them died. However, as a result of multidirectional variability and selection, individual representatives acquired characteristics that contributed to survival in new conditions. The first terrestrial spore plants appeared - psilophytes. They had a cylindrical stem about 25 cm in height, 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 conduction system.

In the Devonian, the number of psilophytes sharply decreased, they were replaced by their transformed descendants, higher plants - lycophytes, mossy And fern-like, in which real vegetative organs (root, stem, leaf) develop. The emergence of vegetative organs increased the efficiency of the function of individual parts of plants and their vitality as a harmoniously integral 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 invertebrate land dwellers were spiders, scorpions, centipedes. There were many fish in the Devonian seas, among them - jaw armored, having an internal cartilaginous skeleton and an external durable shell, movable jaws, and paired fins. Fresh water bodies were 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 dry, they crawled into other reservoirs. A group of lobe-finned fish were the ancestors of ancient amphibians - stegocephalus. Stegocephalians lived in swampy areas, came onto land, but reproduced only in water.

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

During the Permian period, the climate became drier and colder, which led to the extinction of many amphibians. Towards 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-forming ferns replaced seed ferns, which gave rise to gymnosperms. The latter had a developed tap root system and seeds, and fertilization took place in the absence of water. The extinct amphibians were replaced by a more progressive group of animals descended from stegocephalians - reptiles. They had dry skin, denser cellular lungs, internal fertilization, a supply of nutrients in the egg, and protective egg membranes.

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 settled widely reptiles: Ichthyosaurs lived in the seas, plesiosaurs lived in the air - flying lizards, reptiles were also represented on the ground in a variety of ways. Giant reptiles (brontosaurus, diplodocus, etc.) soon became extinct. At the very beginning of the Triassic, a group of small animals with a more advanced skeletal and dental structure separated from reptiles. These animals acquired the ability to give birth, a constant body temperature, they had a four-chambered heart and a number of other progressive organizational features. These were the first primitive mammals.
In the deposits of the Jurassic period of the Mesozoic o6 the remains of the first bird were also found - Archeopteryx. It combined in its structure the characteristics of birds and reptiles.

In the Cretaceous period of the Mesozoic, a branch of plants that had a seed reproduction organ, the flower, separated from the gymnosperms. After fertilization, the ovary of the flower turns into a fruit, so the developing seeds inside the fruit are protected by the pulp and membranes from unfavorable environmental conditions. The variety of flowers and various adaptations for pollination and distribution of fruits and seeds allowed angiosperm (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, greatly contributed to their progressive evolution. In the same period there appeared real birds And placental mammals. Signs of a high degree of organization in them are a constant body temperature | complete separation of arterial and venous blood flow, increased metabolism, perfect thermoregulation, and in mammals, in addition, viviparity, feeding of young with milk, development of the cerebral cortex - allowed these groups to also occupy a dominant position on Earth.

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

In the Paleogene, Neogene and early Quaternary period, flowering plants, thanks to the acquisition of numerous individual adaptations, occupied most of the land and represented subtropical and tropical flora. Due to the cooling caused by the advance of the glacier, the subtropical flora retreated to the south. The composition of terrestrial vegetation of temperate latitudes began to predominate deciduous trees, adapted to the seasonal rhythm of temperatures, as well as shrubs and herbaceous plants. The flowering of herbaceous plants occurs in the Quaternary period. Warm-blooded animals have become widespread:
birds and mammals. During the Ice Age, cave bears, lions, mammoths, and woolly rhinoceroses lived, which gradually died out after the retreat of glaciers and warming of the climate, and the animal world acquired its modern appearance.

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, which led an arboreal lifestyle and fed on plants and insects. Their distant descendants are living today gibbons, orangutans and extinct small tree monkeys - Dryopithecus. Dryopithecus gave rise to three lines of development that led to chimpanzee, gorilla, and also extinct Australopithecus. Originated from Australopithecus at the end of the Neogene a reasonable person.

To understand what era it is now, you need to look at the decision of the Second Session of the International Geological Congress, held in 1881. Then scientists argued about our planet. There were several points of view, which brought confusion to science. By a general vote of experts, it was decided that the modern geological era is Cenozoic. It began 66 million years ago and continues to this day.

Features of the Cenozoic

Of course, the modern geological era is not something monolithic and monotonous. It is divided into three Neogene and Quaternary. During this time, the world has changed dramatically. In the early stages of the Cenozoic, the Earth looked completely different from what it does today, including in terms of flora and fauna. However, it was then that several events occurred, as a result of which the planet became the way we know it.

The restructuring of the worldwide system of interconnected sea currents has begun. It was caused by unprecedented continental drift. Its consequence was the complication of heat exchange between the equatorial and polar basins.

Continental drift

In the Paleogene, the supercontinent Gondwana broke up. An important event that marked the modern geological era was the collision of India and Asia. Africa “stuck” into Eurasia from the southwest. This is how the southern mountains of the Old World and Iran appeared. Geological periods passed slowly, but the map of the Earth inexorably became similar to today's.

The ancient Tethys Ocean, which separated northern Laurasia and southern Gondwana, disappeared over time. Today, all that remains of it are the seas (Mediterranean, Black and Caspian). Important events also took place in the Southern Hemisphere. Antarctica broke away from Australia and headed towards the pole, turning into a glacial desert. The Isthmus of Panama appeared, which connected South and North America, finally dividing the Pacific and Atlantic oceans.

Paleogene

The first period that opened the modern geological era is the Paleogene (66-23 million years ago). A new stage in the development of the organic world has begun. The transition between the Mesozoic and Cenozoic periods was marked by the mass extinction of a huge number of species. Most people know this disaster from the disappearance of the dinosaurs.

The Mesozoic inhabitants of the Earth were replaced by new mollusks, bony fish and angiosperms. In previous geological periods, reptiles dominated the land. Now they have lost their leading position to mammals. Of the reptiles, only crocodiles, turtles, snakes, lizards and some other species have survived. The modern appearance of amphibians has formed. Birds dominated the air.

Neogene

The generally accepted sequence of geological eras states that the second period of the Cenozoic era was the Neogene, which replaced the Paleogene and preceded the Quaternary period. It began 23 million years ago and ended 1.65 million years ago.

At the end of the Neogene, the organic world finally took on modern features. Discocyclines, Assilines and Nummulites became extinct in the sea. The composition of the organic world on land has changed greatly. Mammals have adapted to life in steppes, dense forests, semi-steppes and semi-deserts, thus colonizing vast areas. It was in the Neogene that proboscis, ungulates and other representatives of the fauna common today (hyenas, bears, martens, badgers, dogs, rhinoceroses, sheep, bulls, etc.) appeared. Primates came out of the forests and populated open spaces. 5 million years ago, the first ancestors of modern humans from the hominid genus appeared. In northern latitudes, heat-loving forms of flora (myrtle, laurel, palm trees) began to disappear.

Formation of modern mountains and seas

In the Neogene, the process of mountain building continued, which determined the modern landscape of the planet. The Cordilleras and Appalachians formed in America, and the Atlas formed in Africa. Mountains appeared in eastern Australia and Hindustan. Marginal seas (Japan and Okhotsk) arose in the western Pacific Ocean. Volcanoes were active, with volcanic arcs rising from the water.

For some time, the level of the World Ocean exceeded the modern level, but by the end of the Neogene it fell again. Glaciation covered not only Antarctica, but also the Arctic. The climate became increasingly unstable and contrasting, which was especially characteristic of the next Quaternary period.

fauna migration

During the Neogene period, the territories were finally united into an integral space. A Mediterranean route appeared between Africa and Europe. The Turgai Sea disappeared in the West Siberian Lowland. It separated Europe from Asia. Once it dried, migration between different parts of the world became easier. Herbivorous horses came from America, and antelopes and bulls came from Asia. Proboscideans have spread beyond Africa. Cats, which at first were saber-toothed and lived only in America, filled Eurasia.

The Isthmus of Panama emerged 4 million years ago. A land connection appeared between the two Americas, which led to an unprecedented migration of animals. The southern fauna remained in a state of isolation throughout the Cenozoic, essentially living on a huge island. Now species unfamiliar to each other have come into contact. The fauna got mixed up. Armadillos, sloths and marsupials have appeared in the north. Horses, tapirs, hamsters, pigs, deer and camelids (llamas) colonized South America. The northern fauna has become richer. But in South America a real catastrophe occurred. Due to new competitors in the form of ungulates and predators, many rodents and marsupials became extinct. These controversial events became known as the Great American Exchange.

Quaternary period

It took several billion years for numerous geological eras and periods to succeed each other and finally come to the point where the Quaternary period of the Cenozoic began one and a half million years ago. It continues to this day, so it can be considered modern.

All periods and eras differ from each other in unique ways. The Quaternary is also called the Anthropocene, since it was during this period of time that the development and formation of man occurred. Its first ancestors appeared in East Africa. Then they settled in Eurasia, and from modern Chukotka they came to America. People have gone through several stages of development. The last one (homo sapiens) occurred 40 thousand years ago.

At the same time, it is unique for its climatic changes. Over the past million years, several ice ages have passed, followed by warming periods. Climate change has led to the extinction of many heat-loving species of flora and fauna. Animals that adapted to life in the Ice Age (mammoths, saber-toothed tigers) also disappeared.

Holocene

The answer to the question of what era is now has already been found (Cenozoic). At the same time, within its framework the Quaternary period continues today. It is also divided into parts. The modern department of the Quaternary period is the Holocene era. It began 12 thousand years ago. Scientists call it an interglacial. That is, this is the period that came after significant warming.

At the same time, modern humanity has experienced several minor ice ages. Climatic changes, characteristic of the entire Quaternary period, have repeated cyclically several times over the past 12 thousand years. At the same time, they remain miniature in scale and not so much dramatic. Climatologists note the Little Ice Age, which occurred between 1450 and 1850. Winter temperatures in Europe have dropped, leading to frequent crop failures and disruption to the agricultural economy. The Little Ice Age was preceded by the Atlantic Optimum (900-1300). During this period, the climate was noticeably milder, and glaciers shrank significantly. Here it should be remembered that the Vikings, who discovered Greenland in the Middle Ages, called it a “green country,” although today it is not “green” at all.

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 the 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 towards 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 of animals existed only for certain periods of time, their fossil remains allow geologists to compare sediments of the same age that occur 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 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 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] .

  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 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. Live representatives of lobe-fins, about 1.5 m long, were caught off the east coast of South Africa.

  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. Continents rose all over the 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 the 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:

1. Triassic
2. Jurassic
3. 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-hipped) 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. The ankylosaur, 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 have reached the highest point of their development.

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

  During the Miocene, another series of uplifts created the Sierra Nevada and new ranges in the Rocky Mountains, which created 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. Today's living monotremes could survive for so long only 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 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 different 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 grouped 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 marmot-like animal 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 ones, 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. The plant tissues are in most cases too soft to yield good fossil remains, and the intermediate forms which serve as links between the different types of animals were apparently skeletal forms of which no trace remains. 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.

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 plant world of the Earth - from the simplest single-celled bacteria to modern highly developed flowering plants. The author depicts this long path of development in close connection with the general history of the Earth, with changes in its natural conditions, topography, and 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.

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 reduced to a small number of clearly expressed chemical reactions and does not require previous 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 plant world, 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