The history of planet Earth already goes back approximately 7 billion years. During this time, our common home has undergone significant changes, which was a consequence of changing periods. in chronological order they reveal the entire history of the planet from its very appearance to the present day.
Geological chronology
The history of the Earth, presented in the form of eons, groups, periods and eras, is a certain grouped chronology. At the first international congresses of geology, a special chronological scale was developed, which represented the periodization of the Earth. Subsequently, this scale was replenished with new information and changed, as a result, now it reflects all geological periods in chronological order.
The largest divisions on this scale are eonothems, eras and periods.
Formation of the Earth
The geological periods of the Earth in chronological order begin their history precisely with the formation of the planet. Scientists have concluded that the Earth was formed approximately 4.5 billion years ago. The process of its formation itself was very long and may have begun 7 billion years ago from small cosmic particles. Over time, the gravitational force grew, and along with it, the speed of the bodies falling onto the forming planet increased. Kinetic energy was transformed into heat, resulting in a gradual warming of the Earth.
The Earth's core, according to scientists, was formed over several hundred million years, after which the gradual cooling of the planet began. Currently, the molten core contains 30% of the Earth's mass. The development of other shells of the planet, according to scientists, has not yet been completed.
Precambrian eon
In the geochronology of the Earth, the first eon is called the Precambrian. It covers the time 4.5 billion - 600 million years ago. That is, the lion's share of the planet's history is covered by the former. However, this eon is divided into three more - Katarchean, Archean, Proterozoic. Moreover, often the first of them stands out as an independent eon.
At this time, the formation of land and water occurred. All this happened during active volcanic activity for almost the entire eon. The shields of all continents were formed in the Precambrian, but traces of life are very rare.
Catarchaean Eon
The beginning of the history of the Earth - half a billion years of its existence in science is called catarchaeum. The upper limit of this eon is located at around 4 billion years ago.
Popular literature portrays catarchaea as a time of active volcanic and geothermal changes on the Earth's surface. However, in reality this is not true.
The Catarchaean Eon is a time when volcanic activity did not manifest itself, and the surface of the Earth was a cold, inhospitable desert. Although earthquakes occurred quite often, which smoothed the landscape. The surface looked like dark gray primordial material covered with a layer of regolith. A day at that time was only 6 hours long.
Archean eon
The second main eon of four in the history of the Earth lasted about 1.5 billion years - 4-2.5 billion years ago. At that time, the Earth did not yet have an atmosphere, therefore there was no life yet, however, during this eon, bacteria appeared; due to the lack of oxygen, they were anaerobic. As a result of their activities, today we have deposits of natural resources such as iron, graphite, sulfur and nickel. The history of the term “archaea” dates back to 1872, when it was proposed by the famous American scientist J. Dan. The Archean eon, unlike the previous one, is characterized by high volcanic activity and erosion.
Proterozoic eon
If we consider geological periods in chronological order, the next billion years were occupied by the Proterozoic. This period is also characterized by high volcanic activity and sedimentation, and erosion continues over vast areas.
The formation of the so-called occurs. mountains Currently they are small hills on the plains. The rocks of this eon are very rich in mica, non-ferrous metal ores and iron.
It should be noted that in the Proterozoic period the first living beings appeared - simple microorganisms, algae and fungi. And by the end of the eon, worms, marine invertebrates, and mollusks appear.
Phanerozoic eon
All geological periods in chronological order can be divided into two types - obvious and hidden. Phanerozoic belongs to the obvious ones. At this time, a large number of living organisms with mineral skeletons appear. The era preceding the Phanerozoic was called hidden because practically no traces of it were found due to the lack of mineral skeletons.
The last about 600 million years of the history of our planet are called the Phanerozoic eon. The most significant events of this eon are the Cambrian explosion, which occurred approximately 540 million years ago, and the five largest extinctions in the history of the planet.
Eras of the Precambrian Eon
During the Katarchean and Archean there were no generally recognized eras and periods, so we will skip their consideration.
The Proterozoic consists of three large eras:
Paleoproterozoic- i.e. ancient, including the Siderian, Rhiasian period, Orosirium and Staterium. By the end of this era, oxygen concentrations in the atmosphere had reached modern levels.
Mesoproterozoic- average. Consists of three periods - potassium, ectasia and sthenia. During this era, algae and bacteria reached their greatest prosperity.
Neoproterozoic- new, consisting of Thonium, Cryogenium and Ediacaran. At this time, the formation of the first supercontinent, Rodinia, occurred, but then the plates diverged again. The coldest ice age occurred during an era called the Mesoproterozoic, during which much of the planet froze.
Eras of the Phanerozoic eon
This eon consists of three large eras, sharply different from each other:
Paleozoic, or the era of ancient life. It began approximately 600 million years ago and ended 230 million years ago. The Paleozoic consists of 7 periods:
- Cambrian (a temperate climate formed on Earth, the landscape was lowland, during this period the birth of all modern types of animals occurred).
- Ordovician (the climate throughout the planet is quite warm, even in Antarctica, while the land subsides significantly. The first fish appear).
- Silurian period (large inland seas are formed, while the lowlands become drier due to the rise of land. The development of fish continues. The Silurian period is marked by the appearance of the first insects).
- Devonian (appearance of the first amphibians and forests).
- Lower Carboniferous (dominance of pteridophytes, distribution of sharks).
- Upper and Middle Carboniferous (appearance of the first reptiles).
- Perm (most ancient animals die out).
Mesozoic, or the time of reptiles. Geological history consists of three periods:
- Triassic (seed ferns die out, gymnosperms dominate, the first dinosaurs and mammals appear).
- Jurassic (part of Europe and western America covered with shallow seas, appearance of the first toothed birds).
- Cretaceous (the appearance of maple and oak forests, the highest development and extinction of dinosaurs and toothed birds).
Cenozoic, or the time of mammals. Consists of two periods:
- Tertiary. At the beginning of the period, predators and ungulates reach their dawn, the climate is warm. There is a maximum expansion of forests, the oldest mammals are dying out. Approximately 25 million years ago, humans appeared and in the Pliocene era.
- Quaternary. Pleistocene - large mammals die out, human society emerges, 4 ice ages occur, many plant species become extinct. Modern era - the last ice age ends, the climate gradually takes on its current form. The primacy of man on the entire planet.
The geological history of our planet has a long and contradictory development. In this process, there were several extinctions of living organisms, ice ages were repeated, periods of high volcanic activity were observed, and there were eras of dominance of different organisms: from bacteria to humans. The history of the Earth began approximately 7 billion years ago, it was formed about 4.5 billion years ago, and just less than a million years ago, man ceased to have competitors in all living nature.
Archean era- this is the first stage in the development of life on earth, spanning a time interval of 1.5 billion years. It originates 4 billion years ago. During the Archean era, the flora and fauna of the planet began to emerge, and the history of dinosaurs, mammals and humans began from here. The first deposits of natural resources appear. There were no mountain heights and no ocean, there was not enough oxygen. The atmosphere was mixed with the hydrosphere into a single whole - this prevented the sun's rays from reaching the earth.
Archean era translated from ancient Greek means “ancient.” This era is divided into 4 periods - Eoarchean, Paleoarchean, Mesoarchean and Neoarchean.
The first period of the Archean era lasted approximately 400 million years. This period is characterized by increased meteorite showers, the formation of volcanic craters and the earth's crust. The active formation of the hydrosphere begins, and salty bodies of hot water appear, isolated from each other. Carbon dioxide predominates in the atmosphere; air temperatures reach 120 °C. The first living organisms appear - cyanobacteria, which begin to produce oxygen through photosynthesis. The formation of Vaalbara, the main earthly continent, takes place.
Paleoarchaean
The next period of the Archean era covers a period of time of 200 million years. The Earth's magnetic field is strengthened by increasing the hardness of the earth's core. This has a beneficial effect on the living conditions and development of simple microorganisms. A day lasts about 15 hours. The formation of the world's oceans takes place. Changes in underwater ridges lead to a slow increase in the volume of water and a decrease in the amount of carbon dioxide in the atmosphere. The formation of the first earth's continent continues. Mountain ranges do not yet exist. Instead, active volcanoes rise above the ground.
Mesoarchean
The third period of the Archean era lasted 400 million years. At this time, the main continent splits into two parts. As a result of a sharp cooling of the planet, which is caused by constant volcanic processes, the Pongol glacial formation is formed. During this period, the number of cyanobacteria begins to actively grow. Chemolithotrophic organisms develop that do not require oxygen and sunlight. Vaalbar is fully formed. Its size is approximately equal to the size of modern Madagascar. The formation of the continent of Ur begins. Large islands slowly begin to form from volcanoes. The atmosphere, as before, is dominated by carbon dioxide. The air temperature remains high.
The last period of the Archean era ended 2.5 billion years ago. At this stage, the formation of the earth's crust is completed, and the level of oxygen in the atmosphere increases. The continent of Ur becomes the basis of Kenorland. Most of the planet is occupied by volcanoes. Their active activity leads to increased formation of minerals. Gold, silver, granites, diorites and other equally important natural resources were formed during the Neoarchean period. IN last centuries of the Archean era The first multicellular organisms appear, which were later divided into terrestrial and sea inhabitants. Bacteria begin to develop the sexual process of reproduction. Haploid microorganisms have one set of chromosomes. They constantly adapt to changes in their environment, but at the same time they do not develop other properties. The sexual process allowed adaptation to life with changes in the set of chromosomes. This made it possible for the further evolution of living organisms.
Flora and fauna of the Archean era
The flora of this era cannot boast of diversity. The only plant species are unicellular filamentous algae - spheromorphids - the habitat of bacteria. When these algae form in colonies, they can be seen without special instruments. They can go free swimming or attach to the surface of something. In the future, the algae will form a new form of life - lichens.
During the Archean era the first prokaryotes- single-celled organisms that do not have a nucleus. Through photosynthesis, prokaryotes produce oxygen and create favorable conditions for the emergence of new life forms. Prokaryotes are divided into two domains - bacteria and archaea.
Archaea
It has now been established that they have features that distinguish them from other living organisms. Therefore, the classification that combines them with bacteria into one group is considered outdated. Externally, archaea are similar to bacteria, but some have unusual shapes. These organisms can absorb both sunlight and carbon. They can exist in the most unsuitable conditions for life. One type of archaea is food for marine life. Several species have been found in the human intestine. They take part in the digestive processes. Other types are used to clean sewage ditches and ditches.
There is a theory, unconfirmed by facts, that during the Archean era the birth and development of eukaryotes - microorganisms of the fungal kingdom, similar to yeasts - occurred.
The fact that life on earth originated during the Archean era is evidenced by the found fossilized stromalites - waste products of cyanobacteria. The first stromatolites were discovered in Canada, Siberia, Australia and Africa. Scientists have proven that it was bacteria that had a huge impact on the formation of aragonite crystals, which is found in mollusk shells and is part of corals. Thanks to cyanobacteria, deposits of carbonate and siliceous formations arose. Colonies of ancient bacteria look like mold. They were located in the area of volcanoes, and at the bottom of lakes, and in coastal areas.
Archean Climate
Scientists have not yet been able to find out anything about the climate zones of this period. The existence of zones of different climates in the Archean era can be judged by ancient glacial deposits - tillites. Remains of glaciations have been found in America, Africa, and Siberia today. It is not yet possible to determine their true size. Most likely, glacial deposits covered only mountain peaks, because vast continents had not yet been formed during the Archean era. The existence of a warm climate in some areas of the planet is indicated by the development of flora in the oceans.
Hydrosphere and atmosphere of the Archean era
In the early period there was little water on earth. The water temperature during the Archean era reached 90°C. This indicates the saturation of the atmosphere with carbon dioxide. There was very little nitrogen in it, there was almost no oxygen in the early stages, the remaining gases are quickly destroyed under the influence of sunlight. The atmospheric temperature reaches 120 degrees. If nitrogen predominated in the atmosphere, then the temperature would not be lower than 140 degrees.
In the late period, after the formation of the world ocean, the level of carbon dioxide began to decrease noticeably. The temperature of water and air also dropped. And the amount of oxygen increased. Thus, the planet gradually became suitable for life of various organisms.
Archean minerals
It was during the Archean era that the greatest formation of minerals occurred. This is facilitated by the active activity of volcanoes. Colossal deposits of iron, gold, uranium and manganese ores, aluminum, lead and zinc, copper, nickel and cobalt ores were laid down by this era of the earth's life. On the territory of the Russian Federation, Archean deposits have been found in the Urals and Siberia.
In details periods of the Archean era will be discussed in subsequent lectures.
The idea of how life originated in the ancient eras of the Earth give us fossil remains of organisms, but they are distributed into separate geological periods extremely uneven.
Geological periods
The era of ancient life on Earth includes 3 stages of the evolution of flora and fauna.
Archean era
Archean era- the oldest era in the history of existence. It began about 4 billion years ago. And the duration is 1 billion years. This is the beginning of the formation of the earth's crust as a result of the activity of volcanoes and air masses, sudden changes in temperature and pressure. The process of destruction of primary mountains and the formation of sedimentary rocks is underway.
The most ancient Archeozoic layers of the earth's crust are represented by highly altered, otherwise metamorphosed, rocks, which is why they do not contain noticeable remains of organisms.
But it is completely wrong on this basis to consider the Archeozoic a lifeless era: in the Archeozoic there existed not only bacteria and algae, but also more complex organisms.
Proterozoic era
The first reliable traces of life in the form of extremely rare finds and poor preservation are found in Proterozoic, otherwise - the era of “primary life”. The duration of the Proterozoic era is taken to be about 2 million years
Traces of crawling found in Proterozoic rocks annelids, sponge needles, shells of the simplest forms of brachiopods, arthropod remains.
Brachiopods, distinguished by their exceptional diversity of forms, were widespread in the ancient seas. They are found in sediments of many periods, especially the following, Paleozoic era.
Shell of the brachiopod "Horistites Moskvenzis" (ventral valve)
Only a few species of brachiopods have survived to this day. Most brachiopods had shells with unequal valves: the ventral one, on which they lie or are attached to the seabed with the help of a “leg,” was usually larger than the dorsal one. By this feature, in general, it is not difficult to recognize brachiopods.
The small number of fossil remains in Proterozoic deposits is explained by the destruction of most of them as a result of changes (metamorphization) of the containing rock.
Sediments help judge the extent to which life was represented in the Proterozoic. limestones, which then turned into marble. Limestones obviously owe their origin to a special type of bacteria that produced lime carbonate.
The presence of interlayers in the Proterozoic deposits of Karelia shungite, similar to anthracite coal, suggests that the initial material for its formation was the accumulation of algae and other organic residues.
At this distant time, the ancient land was still not lifeless. Bacteria settled in the vast expanses of the still deserted primary continents. With the participation of these simple organisms, weathering and loosening of the rocks that made up the ancient earth's crust occurred.
According to the assumption of the Russian academician L. S. Berg(1876-1950), who studied how life originated in the ancient eras of the Earth, at that time soils had already begun to form - the basis for the further development of vegetation.
Palaeozoic
Deposits next in time, Paleozoic era, otherwise, the era of “ancient life”, which began about 600 million years ago, differs sharply from the Proterozoic in the abundance and diversity of forms even in the most ancient, Cambrian period.
Based on the study of the remains of organisms, it is possible to reconstruct the following picture of the development of the organic world, characteristic of this era.
There are six periods of the Paleozoic era:
Cambrian period
Cambrian period was described for the first time in England, Cambrian County, where its name came from. During this period, all life was connected with water. These are red and blue-green algae, limestone algae. The algae released free oxygen, which enabled the development of organisms that consumed it.
Close examination of blue-green Cambrian clays, which are clearly visible in deep sections of river valleys near St. Petersburg and especially in the coastal regions of Estonia, made it possible to establish in them (using a microscope) the presence plant spores.
This definitely suggests that some species that existed in bodies of water since the earliest times of the development of life on our planet moved to land approximately 500 million years ago.
Among the organisms that inhabited the most ancient Cambrian reservoirs, invertebrates were exceptionally widespread. Of the invertebrates, in addition to the smallest protozoa - rhizomes, they were widely represented worms, brachiopods and arthropods.
Among arthropods, these are primarily various insects, especially butterflies, beetles, flies, and dragonflies. They appear much later. To the same type of animal world, in addition to insects, also belong arachnids and centipedes.
Among the most ancient arthropods there were especially many trilobites, similar to modern woodlice, only much larger (up to 70 centimeters), and crustacean scorpions, which sometimes reached impressive sizes.
Trilobites - representatives of the animal world of the ancient seas Three lobes are clearly distinguished in the body of a trilobite; it is not for nothing that it is called that: translated from ancient Greek, “trilobos” means three-lobed. Trilobites not only crawled along the bottom and burrowed into the mud, but could also swim.
Among trilobites, generally small forms predominated.
According to geologists, trilobites - “guiding fossils” - are characteristic of many Paleozoic deposits.
The dominant fossils are those that predominate at a given geological time. The age of the sediments in which they are found is usually easily determined from the leading fossils. Trilobites reached their greatest prosperity during the Ordovician and Silurian periods. They disappeared at the end of the Paleozoic era.
Ordovician period
Ordovician period characterized by a warmer and milder climate, as evidenced by the presence of limestones, shale and sandstones in the rock deposits. At this time, the area of the seas increases significantly.
This promotes the reproduction of large trilobites, from 50 to 70 cm in length. Appear in the seas sea sponges, mollusks, and the first corals.
The first corals Silurian
What did the Earth look like in Silurian? What changes occurred on the primeval continents? Judging by the imprints on clay and other stone material, we can definitely say that at the end of the period the first terrestrial vegetation appeared on the shores of reservoirs.
The first plants of the Silurian period
These were small leafy stems plants, which rather resembled sea brown algae, having neither roots nor leaves. The role of leaves was played by green, successively branching stems.
Psilophyte plants - naked plants The scientific name of these ancient progenitors of all land plants (psilophytes, otherwise “naked plants”, i.e. plants without leaves) well conveys their distinctive features. (Translated from ancient Greek “psilos” means bald, naked, and “phytos” means trunk). Their roots were also undeveloped. Psilophytes grew in marshy, marshy soils. An imprint in the rock (right) and a restored plant (left).
Inhabitants of reservoirs of the Silurian period
From inhabitants maritime Silurian reservoirs It should be noted that, in addition to trilobites, corals And echinoderms - sea lilies, sea urchins and stars.
Sea lily "Acantocrinus rex" The crinoids, the remains of which were found in the sediments, bore very little resemblance to predatory animals. Sea lily "Acantocrinus rex" means "thorny king lily". The first word is formed from two Greek words: “acantha” - a thorny plant and “crinone” - lily, the second Latin word “rex” - king.
Cephalopods and especially brachiopods were represented by a huge number of species. In addition to cephalopods that had an internal shell, like belemnites, cephalopods with external shells were widespread in the most ancient periods of the Earth’s life.
The shape of the shell was straight and bent into a spiral. The sink was successively divided into chambers. The largest outer chamber contained the body of the mollusk, the rest were filled with gas. A tube passed through the chambers - a siphon, which allowed the mollusk to regulate the amount of gas and, depending on this, float or sink to the bottom of the reservoir.
Currently, of these cephalopods, only one boat with a coiled shell has been preserved. Ship, or nautilus, which is the same thing, translated from Latin - inhabitant of the warm sea.
The shells of some Silurian cephalopods, such as orthoceras (translated from ancient Greek as “straight horn”: from the words “ortoe” - straight and “keras” - horn), reached gigantic sizes and looked more like a straight two-meter pole than a horn.
Limestones in which orthoceratites occur are called orthoceratitic limestones. Square slabs of limestone were widely used in pre-revolutionary St. Petersburg for sidewalks, and the characteristic sections of orthoceratite shells were often clearly visible on them.
A remarkable event of the Silurian time was the appearance in fresh and brackish bodies of water of clumsy “ armored fish", which had an external bone shell and a non-ossified internal skeleton.
A cartilaginous cord, the notochord, corresponded to the spinal column. Carapaces did not have jaws or paired fins. They were poor swimmers and therefore stuck more to the bottom; Their food was silt and small organisms.
Panzerfish Pterichthys The armored fish Pterichthys was generally a poor swimmer and led a natural lifestyle.
It can be assumed that Bothriolepis was already much more mobile than Pterichthys.
Sea predators of the Silurian period
In later deposits there are already remains sea predators, close to sharks. From these lower fish, which also had a cartilaginous skeleton, only teeth were preserved. Judging by the size of the teeth, for example from Carboniferous deposits of the Moscow region, we can conclude that these predators reached significant sizes.
In the development of the animal world of our planet, the Silurian period is interesting not only because the distant ancestors of fish appeared in its reservoirs. At the same time, another equally important event took place: representatives of arachnids climbed out of the water onto land, among them ancient scorpions, still very close to crustaceans.
Cancer scorpions are inhabitants of shallow seas On the right, at the top is a predator armed with strange claws - Pterygotus, reaching 3 meters, glory - Eurypterus - up to 1 meter long.
Devonian
The land - the arena of the future life - gradually takes on new features, especially characteristic of the next, Devonian period. At this time, woody vegetation appears, first in the form of low-growing shrubs and small trees, and then larger ones. Among the Devonian vegetation we will meet well-known ferns, other plants will remind us of the graceful fir-tree of horsetail and the green ropes of club mosses, only not creeping along the ground, but proudly rising upward.
In later Devonian deposits, fern-like plants also appear, which reproduced not by spores, but by seeds. These are seed ferns, occupying a transitional position between spore and seed plants.
Fauna of the Devonian period
Animal world seas Devonian period rich in brachiopods, corals and crinoids; trilobites begin to play a secondary role.
Among cephalopods, new forms appear, only not with a straight shell, like in Orthoceras, but with a spirally twisted one. They are called ammonites. They received their name from the Egyptian sun god Ammon, near the ruins of whose temple in Libya (Africa) these characteristic fossils were first discovered.
By their general appearance it is difficult to confuse them with other fossils, but at the same time it is necessary to warn young geologists about how difficult it can be to identify individual types of ammonites, the total number of which is not in the hundreds, but in the thousands.
Ammonites reached a particularly magnificent flourishing in the next, Mesozoic era. .
Fish developed significantly in Devonian times. In armored fish, the bony shell was shortened, which made them more mobile.
Some armored fish, such as the nine-meter giant Dinichthys, were terrible predators (in Greek “deinos” means terrible, terrible, and “ichthys” means fish).
The nine-meter-long dinychthys obviously posed a great threat to the inhabitants of reservoirs.
In Devonian reservoirs there were also lobe-finned fish, from which lungfish evolved. This name is explained by the structural features of the paired fins: they are narrow and, in addition, sit on an axis covered with scales. This feature distinguishes lobe-finned fish, for example, from pike-perch, perch and other bony fish called ray-finned fish.
Lobe-finned fish are the ancestors of bony fish, which appeared much later - at the end of the Triassic.
We would have no idea what lobe-finned fish that lived at least 300 million years ago actually looked like if it weren’t for the successful catches of the rarest specimens of their modern generation in the mid-twentieth century off the coast of South Africa.
They apparently live at considerable depths, which is why they are so rarely seen by fishermen. The caught species was named coelacanth. It reached 1.5 meters in length.
In their organization, lungfishes are close to lobe-finned fish. They have lungs corresponding to the swim bladder of a fish.
In their organization, lungfishes are close to lobe-finned fish. They have lungs corresponding to the swim bladder of a fish.
How unusual the lobe-finned fish looked can be judged by a specimen, a coelacanth, caught in 1952 off the Comoros Islands, west of the island of Madagascar. This 1.5 liter long fish weighed about 50 kg.
A descendant of ancient lungfish, the Australian ceratodus (translated from ancient Greek as horntooth) reaches two meters. It lives in drying up reservoirs and, as long as there is water in them, breathes with gills, like all fish, but when the reservoir begins to dry out, it switches to pulmonary respiration.
Australian ceratodus - a descendant of ancient lungfish Its respiratory organs are the swim bladder, which has a cellular structure and is equipped with numerous blood vessels. In addition to Ceratodus, two more species of lungfish are now known. One of them lives in Africa, and the other in South America.
Transition of vertebrates from water to land
Amphibian transformation table.
The oldest fish 
The first picture shows the oldest cartilaginous fish, Diplocanthus (1). Below it is a primitive lobe-finned eusthenopteron (2); below is a supposed transitional form (3). The huge amphibian Eogyrinus (about 4.5 m in length) has limbs that are still very weak (4), and only as they master the land way of life do they become a reliable support, for example, for the heavy Eryops, about 1.5 m in length (5).
This table helps to understand how, as a result of gradual changes in the organs of locomotion (and breathing), aquatic organisms moved to land, how the fin of a fish was transformed into the limb of amphibians (4), and then reptiles (5). At the same time, the spine and skull of the animal change.
The Devonian period dates back to the appearance of the first wingless insects and terrestrial vertebrates. From this we can assume that it was at this time, and perhaps even a little earlier, that the transition of vertebrates from water to land took place.
It was realized through fish in which the swim bladder was modified, like in lungfishes, and the fin-like limbs gradually turned into five-fingered ones, adapted to a terrestrial lifestyle.
Metopoposaurus still had difficulty getting onto land.
Therefore, the closest ancestors of the first land animals should therefore be considered not lungfish, but lobe-finned fish, which adapted to breathing atmospheric air as a result of periodic drying out of tropical reservoirs.
The link between terrestrial vertebrates and lobe-finned animals are ancient amphibians, or amphibians, collectively called stegocephalians. Translated from ancient Greek, stegocephaly means “covered-headed”: from the words “stege” - roof and “mullet” - head. This name is given because the roof of the skull is a rough shell of bones closely adjacent to each other.
There are five holes in the stegocephalus skull: two pairs of holes - ophthalmic and nasal, and one for the parietal eye. In appearance, stegocephals were somewhat reminiscent of salamanders and often reached significant sizes. They lived in swampy areas.
The remains of stegocephals were sometimes found in hollows of tree trunks, where they apparently hid from daylight. In the larval state, they breathed through gills, just like modern amphibians.
Stegocephals found especially favorable conditions for their development in the next Carboniferous period.
Carboniferous period
Warm and humid climate, especially in the first half Carboniferous period, favored the lush flourishing of terrestrial vegetation. The coal forests, never seen by anyone, were, of course, completely different from those of today.
Among those plants that settled in marshy, marshy areas approximately 275 million years ago, giant tree-like horsetails and club mosses clearly stood out in their characteristic features.
Of the tree-like horsetails, calamites were widely used, and of the clubmosses, giant lepidodendrons and, somewhat smaller in size, graceful sigillaria.
In coal seams and the rocks covering them, well-preserved remains of vegetation are often found, not only in the form of clear imprints of leaves and tree bark, but also entire stumps with roots and huge trunks that have turned into coal.
Using these fossil remains, you can not only restore the general appearance of the plant, but also get acquainted with its internal structure, which is clearly visible under a microscope in paper-thin sections of the trunk. Calamites get their name from the Latin word “calamus” - reed, reed.
The slender, hollow inside trunks of the calamites, ribbed and with transverse constrictions, like those of the well-known horsetails, rose in slender columns 20-30 meters from the ground.
Small narrow leaves, collected in rosettes on short stems, gave, perhaps, some resemblance to calamite with the larch of the Siberian taiga, transparent in its elegant decoration.
Nowadays, horsetails - field and forest - are distributed throughout the globe, except Australia. In comparison with their distant ancestors, they seem pitiful dwarfs, which, moreover, especially horsetail, have a bad reputation among farmers.
Horsetail is a nasty weed that is difficult to control, since its rhizome goes deep into the ground and continually produces new shoots.
Large species of horsetails - up to 10 meters in height - are currently preserved only in the tropical forests of South America. However, these giants can only grow by leaning against neighboring trees, since they are only 2-3 centimeters in diameter.
Lepidodendrons and sigillaria occupied a prominent place among the Carboniferous vegetation.
Although they were not similar in appearance to modern mosses, they still resembled them in one characteristic feature. The powerful trunks of lepidodendrons, reaching 40 meters in height and up to two meters in diameter, were covered with a distinct pattern of fallen leaves.
These leaves, while the plant was still young, sat on the trunk in the same way as its small green scales - leaves - sit on the club moss. As the tree grew, the leaves aged and fell off. From these scaly leaves, the giants of the coal forests got their name - lepidodendrons, otherwise - “scaly trees” (from the Greek words: “lepis” - scales and “dendron” - tree).
The traces of fallen leaves on the bark of the sigillaria had a slightly different shape. They differed from lepidodendrons in their smaller height and more slender trunk, which branched only at the very top and ended in two huge bunches of hard leaves, each about a meter long.
An introduction to Carboniferous vegetation would be incomplete without also mentioning cordaites, which are close to conifers in wood structure. These were tall (up to 30 meters), but relatively thin-trunked trees.
Cordaites get their name from the Latin elephant “cor” - heart, since the seed of the plant was heart-shaped. These beautiful trees were crowned with a lush crown of ribbon-like leaves (up to 1 meter in length).
Judging by the structure of the wood, the trunks of the coal giants still did not have the strength that is generally inherent in modern trees. Their bark was much stronger than wood, hence the general fragility of the plant and poor resistance to fracture.
Strong winds and especially storms broke trees, felled huge forests, and to replace them again, new lush growth grew from the swampy soil... The felled wood served as the source material from which powerful layers of coal were subsequently formed.
Lepidodendrons, otherwise known as scaly trees, reached enormous sizes.
It is not correct to attribute the formation of coal only to the Carboniferous period, since coals also occur in other geological systems.
For example, the oldest Donetsk coal basin was formed during the Carboniferous era. The Karaganda pool is the same age as it.
As for the largest Kuznetsk basin, only a small part of it belongs to the Carboniferous system, and mainly to the Permian and Jurassic systems.
One of the largest basins - the “Polar Stoker” - the richest Pechora basin, was also formed mainly in the Permian period and, to a lesser extent, in the Carboniferous period.
Flora and fauna of the Carboniferous period
For marine sediments Carboniferous period Representatives of the simplest animals from the class are especially characteristic rhizomes. The most typical were fusulines (from the Latin word “fusus” - “spindle”) and schwagerins, which served as the starting material for the formation of strata of fusuline and schwagerin limestones.
Carboniferous rhizomes: 1 - fusulina; 2 - schwagerina Carboniferous rhizomes - fusulin (1) and schwagerina (2) are enlarged 16 times.
Elongated, like grains of wheat, fusulines and almost spherical schwagerins are clearly visible on the limestones of the same name. Corals and brachiopods developed magnificently, giving rise to many leading forms.
The most widespread were the genus productus (translated from Latin - “stretched”) and spirifer (translated from the same language - “carrying spiral”, which supported the soft “legs” of the animal).
Trilobites, which dominated in previous periods, are found much less frequently, but on land other representatives of arthropods are beginning to become noticeably widespread - long-legged spiders, scorpions, huge centipedes (up to 75 centimeters in length) and especially gigantic insects, similar to dragonflies, with a wingspan. up to 75 centimeters! The largest modern butterflies in New Guinea and Australia reach a wingspan of 26 centimeters.
The oldest Carboniferous dragonfly The ancient Carboniferous dragonfly seems like an enormous giant compared to the modern one.
Judging by the fossil remains, sharks have noticeably multiplied in the seas.
Amphibians, firmly established on land during Carboniferous times, go through a further development path. The dry climate, which increased at the end of the Carboniferous period, gradually forced ancient amphibians to move away from an aquatic lifestyle and move primarily to a terrestrial existence.
These organisms, transitional to a new way of life, laid eggs on land, and did not spawn in the water, like amphibians. The offspring hatched from the eggs acquired characteristics that sharply distinguished them from their ancestors.
The body was covered, like a shell, with scale-like outgrowths of the skin, protecting the body from loss of moisture through evaporation. So reptiles, or reptiles, separated from amphibians (amphibians). In the next Mesozoic era, they conquered land, water and air.
Permian period
Last Paleozoic period - Permian- was significantly shorter in duration than the Carboniferous. It should be noted, in addition, the great changes that have occurred on the ancient geographical map of the world - land, as confirmed by geological research, gains significant dominance over the sea.
Plants of the Permian period
The climate of the northern continents of the Upper Permian was dry and sharply continental. Sandy deserts have become widespread in some places, as evidenced by the composition and reddish tint of the rocks that make up the Permian formation.
This time was marked by the gradual extinction of the giants of the coal forests, the development of plants close to conifers, and the appearance of cycads and ginkgos, which became widespread in the Mesozoic.
Cycad plants have a spherical and tuberous stem immersed in the soil, or, conversely, a powerful columnar trunk up to 20 meters high, with a lush rosette of large feathery leaves. In appearance, cycad plants resemble the modern sago palm of tropical forests in the Old and New Worlds.
Sometimes they form impenetrable thickets, especially on the flooded banks of the rivers of New Guinea and the Malay Archipelago (Great Sunda Islands, Lesser Sunda Islands, Moluccas and Philippine Islands). Nutritious flour and cereals (sago) are made from the soft pith of the palm tree, which contains starch.
Forest of sigillaries Sago bread and porridge are the daily food of millions of inhabitants of the Malay Archipelago. Sago palm is widely used in housing construction and household products.
Another very peculiar plant, ginkgo, is also interesting because it has survived in the wild only in some places in Southern China. Ginkgo has been carefully cultivated near Buddhist temples since time immemorial.
Ginkgo was brought to Europe in the mid-18th century. Now it is found in park culture in many places, including here on the Black Sea coast. Ginkgo is a large tree up to 30-40 meters in height and up to two meters thick, in general it resembles a poplar, but in its youth it is more like some conifers.
Branch of modern Ginkgo biloba with fruits The leaves are petiolate, like those of aspen, have a fan-shaped plate with fan-shaped venation without transverse bridges and a notch in the middle. In winter the leaves fall off. The fruit, a fragrant drupe like a cherry, is edible in the same way as the seeds. In Europe and Siberia, ginkgo disappeared during the Ice Age.
Cordaites, conifers, cycads and ginkgo belong to the group of gymnosperms (since their seeds lie open).
Angiosperms - monocotyledons and dicotyledons - appear somewhat later.
Fauna of the Permian period
Among the aquatic organisms that inhabited the Permian seas, ammonites stood out noticeably. Many groups of marine invertebrates, such as trilobites, some corals and most brachiopods, became extinct.
Permian period characteristic of the development of reptiles. The so-called bestial lizards deserve special attention. Although they possessed some features characteristic of mammals, such as teeth and skeletal features, they still retained a primitive structure that brought them closer to stegocephals (from which reptiles originated).
The beast-like Permian lizards were distinguished by their considerable size. The sedentary herbivorous pareiasaurus reached two and a half meters in length, and the formidable predator with tiger teeth, otherwise known as the “animal-toothed lizard” - inostrantseviya, was even larger - about three meters.
Pareiasaurus translated from ancient Greek means “cheeked lizard”: from the words “pareia” - cheek and “sauros” - lizard, lizard; The wild-toothed lizard Inostracevia is named so in memory of the famous geologist - prof. A. A. Inostrantseva (1843-1919).
The richest finds from the ancient life of the Earth, the remains of these animals, are associated with the name of the enthusiastic geologist Prof. V. P. Amalitsky(1860-1917). This persistent researcher, without receiving the necessary support from the treasury, nevertheless achieved remarkable results in his work. Instead of a well-deserved summer rest, he and his wife, who shared all the hardships with him, went in a boat with two oarsmen in search of the remains of bestial lizards.
Persistently, for four years he conducted his research on the Sukhona, Northern Dvina and other rivers. Finally, he managed to make discoveries that were extremely valuable for world science on the Northern Dvina, not far from the city of Kotlas.
Here, in the coastal cliff of the river, concretions of the bones of ancient animals (concretions - stone accumulations) were discovered in thick lentils of sand and sandstone, among striped rudders. The collection of just one year of work by geologists took two freight cars during transportation.
Subsequent developments of these bone-bearing accumulations further enriched the information about Permian reptiles.
Place of finds of Permian dinosaurs Place of finds of Permian dinosaurs discovered by the professor V. P. Amalitsky in 1897. The right bank of the Malaya Northern Dvina River near the village of Efimovka, near the city of Kotlas.
The richest collections taken from here amount to tens of tons, and the skeletons collected from them represent in the Paleontological Museum of the Academy of Sciences a rich collection, which has no equal in any museum in the world.
Among the ancient animal-like Perm reptiles, the original three-meter predator Dimetrodon stood out, otherwise “two-dimensional” in length and height (from the ancient Greek words: “di” - twice and “metron” - measure).
Beastlike Dimetrodon Its characteristic feature is the unusually long processes of the vertebrae, forming a high ridge on the animal’s back (up to 80 centimeters), apparently connected by a skin membrane. In addition to predators, this group of reptiles also included plant- or molluscivorous forms, also of very significant size. The fact that they ate shellfish can be judged by the structure of their teeth, suitable for crushing and grinding shells. (No ratings yet)
And the Universe. For example, the Kant-Laplace hypothesis, O.Yu. Schmidt, Georges Buffon, Fred Hoyle and others. But most scientists are inclined to believe that the Earth is about 5 billion years old.
The events of the geological past in their chronological sequence are represented by a unified international geochronological scale. Its main divisions are the eras: Archean, Proterozoic, Paleozoic, Mesozoic. Cenozoic. The oldest interval of geological time (Archean and Proterozoic) is also called Precambrian. It covers a long period - almost 90% of the whole (the absolute age of the planet, according to modern concepts, is taken to be 4.7 billion years).
Within eras, smaller time periods are distinguished - periods (for example, Paleogene, Neogene and Quaternary in the Cenozoic era).
In the Archean era (from Greek - primordial, ancient), crystalline rocks (granites, gneisses, schists) were formed. During this era, powerful mountain-building processes did not take place. The study of this era allowed geologists to assume the presence of seas and living organisms in them.
The Proterozoic era (the era of early life) is characterized by rock deposits in which the remains of living organisms were found. During this era, the most stable areas - platforms - formed on the surface of the Earth. The platforms - these ancient cores - became centers of formation.
The Paleozoic era (the era of ancient life) is distinguished by several stages of powerful mountain building. During this era, the Scandinavian mountains, the Urals, Tien Shan, Altai, and Appalachians arose. At this time, animal organisms with a hard skeleton appeared. Vertebrates appeared for the first time: fish, amphibians, reptiles. In the Middle Paleozoic, land vegetation appeared. Tree ferns, moss ferns, etc. served as material for the formation of coal deposits.
The Mesozoic era (the era of middle life) is also characterized by intense folding. Mountains formed in areas adjacent to. Reptiles (dinosaurs, proterosaurs, etc.) dominated among animals; birds and mammals appeared for the first time. The vegetation consisted of ferns, conifers, and angiosperms appeared at the end of the era.
During the Cenozoic era (the era of new life), the modern distribution of continents and oceans took shape, and intense mountain-building movements occurred. Mountain ranges are formed on the shores of the Pacific Ocean, in southern Europe and Asia (the Himalayas, the Cordillera Coastal Ranges, etc.). At the beginning of the Cenozoic era, the climate was much warmer than today. However, the increase in land area due to the rise of continents led to cooling. Extensive ice sheets appeared in the north and. This led to significant changes in the flora and fauna. Many animals became extinct. Plants and animals close to modern ones appeared. At the end of this era, man appeared and began to intensively populate the land.
The first three billion years of Earth's development led to the formation of land. According to scientists, at first there was one continent on Earth, which subsequently split into two, and then another division occurred, and as a result, five continents were formed today.
The last billion years of Earth's history are associated with the formation of folded regions. At the same time, in the geological history of the last billion years, several tectonic cycles (epochs) are distinguished: Baikal (end of the Proterozoic), Caledonian (early Paleozoic), Hercynian (late Paleozoic), Mesozoic (Mesozoic), Cenozoic or Alpine cycle (from 100 million years to present tense).
As a result of all the above processes, the Earth acquired its modern structure.
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]
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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]
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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]
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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]
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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]
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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]
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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:
- 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-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. 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 have reached the highest point of their 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.
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. 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 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 deposits, 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.