4th period of the Paleozoic. Paleozoic

The appearance of eukaryotes marked the beginning of the emergence of multicellular plants and animals in the Upper Riphean about 1.4–1.3 billion years ago, which appeared almost simultaneously (Sokolov, 1975).

The increase in oxygen content in the aquatic environment and atmosphere has become the leading environmental factor in the development of life on Earth. It was photosynthetic microscopic algae that predetermined the formation of highly organized life on the planet and the biosphere as a whole.

In the Vendian, between two phases of glaciation, the Ediacaran fauna arose and became widespread, immediately preceding the fauna of skeletal organisms. It was represented by invertebrates: coelenterates and the first organisms with a nervous system - worms. A distinctive feature of the Ediacaran fauna is that its representatives did not have skeletons. Although some of them reached sizes up to 1 m (jellyfish), they consisted of a jelly-like substance, probably enclosed in a denser outer layer. Among them were organisms leading a benthic lifestyle, as well as passively or actively moving in the water column. The amazing preservation of the prints of Ediacaran animals can be explained by the absence of predators, as well as saprophages and ground beetles.

If until the end of the Proterozoic the evolution of life on Earth was extremely slow, then during the Phanerozoic there were quite fast, spasmodic changes organic world planets. The driving force behind this evolution has been natural selection, which was determined by the ability of organisms to transform under conditions of limited food resources of the emerging biosphere, as well as changes in physical and geographical conditions. Natural selection has evolved the ability of organisms to adapt to dynamic natural environment. Yes, saturation. aquatic environment oxygen turned out to be disastrous for most anaerobic representatives of organic life, and only a few species were able to adapt to new conditions.

Development of life in the Paleozoic

The rapid development of life began in the Paleozoic era, which is divided into two stages: early and late. The early stage, including the Cambrian (570–500 Ma), Ordovician (500–440 Ma) and Silurian (440–400 Ma), coincided with the Caledonian tectonic cycle.

The split of the early supercontinent that began at the end of the Proterozoic led in the Cambrian to the formation of the huge continent of Gondwana, which included modern Africa, South America, India, Australia and Antarctica, as well as to the emergence of the Baltic, Siberian, Chinese and North American microcontinents. The transgression of the sea at the beginning of the Cambrian was replaced by a regression in the second half of this period.

In the Cambrian warm seas, whose waters acquired a chemical composition close to the modern one, blue-green algae were widely developed, as evidenced by traces of their vital activity - stromatolites. The flora was also abundantly represented by algae. At the same time, the Cambrian is a time of rapid development of arthropods, especially trilobites; remains of both soft-bodied and rigid-bodied animals with an external skeleton (shell) animals have been preserved in the Cambrian deposits. The evolution of skeletal organisms was prepared by the entire evolution of the organic world of the ancient aquatic environment, including the appearance of predators, as well as the transition to living on the bottom and in other likely conditions. Since that time, biogenic sedimentation in OK(U) HC has become predominant.

The oxygen content in the atmosphere during the Cambrian period reached approximately 1% of the current level. Accordingly, the content has been reduced. carbon dioxide and possibly water vapor. This weakened the greenhouse effect of the atmosphere, made it more transparent due to a decrease in cloudiness. The role of sunlight in biological, geochemical, and lithogenesis processes began to sharply increase. The moderately warm and dry climate of the Cambrian was distinguished by relative diversity, including periods of cooling, up to the formation of glacial deposits.

So far, there is no convincing evidence of the existence of any living organisms on land in the Cambrian. Terrestrial higher plants that would produce spores and pollen did not yet exist, although the colonization of land by bacteria and blue-green algae is not excluded. Since there are no traces of coal accumulation in the Cambrian deposits, it can be argued that there was no abundant and highly organized vegetation on land. Life was concentrated in the shallow waters of the epicontinental seas, i.e. seas on continents.

Paleozoic skeleton. Photo: Dallas Krentzel

An ancestor of the crocodile from the Paleozoic period. Photo: Scott Heath

At the beginning of the Ordovician, the evolution of the organic world became more intense than in the Cambrian, and led to the emergence of new families. During this period, Gondwana continued to exist with the Chinese mainland attached to it. Baltic, Siberian and North American microcontinents.

In the first half of the Ordovician, an extensive transgression of the sea occurred, as a result of which more than 83% of the surface was under water. the globe. Almost all modern continents were flooded. The most characteristic sedimentary deposits of this time are biogenic limestones and dolomites - indicators of a warm climate. In warm seas, trilobites have become widespread, replacing the Cambrian chitinous skeleton with a calcareous one. In addition to them and microorganisms (bacteria, blue-green algae and algae), characteristic animals of the aquatic environment were graptolites, tabulates, brachiopods, echinoderms, archaeocyates, cephalopods and others. in the Ordovician, the first vertebrates appeared - jawless fish-like with a two-chambered heart and a simply arranged brain, protected by an air paracerebral capsule. Further development marine vertebrates followed the path of complication of the brain (cyfalization), the circulatory system and all other organs and systems.

At the end of the Ordovician, the regression of the sea began, associated with one of the early phases of the Caledonian folding, which received greatest development and distribution in the next, Silurian period. This regression was accompanied by a cooling of the climate. In the changed paleogeographic conditions, there was a mass extinction of representatives marine fauna.

Most of the crises in the development of fauna, both in the Late Ordovician and in previous and subsequent geological periods, coincided with the epochs of temperature minima, and the largest of them coincided with the epochs of glaciations (Ushakov and Yasamanov, 1984). All other factors of the natural environment are somehow related to the climate. The conjugation of the organic world with the climate determined the evolution of the biosphere. Extinction crises were usually followed by epochs of extraordinary flourishing of life. Organisms did not just settle, mastering new habitats, their evolution took place at an increasing speed. It is the unity of organisms and the environment, as one of the fundamental laws of biology, with an increase in the capabilities of the organisms themselves, that suggests the presence of diverse forms of adaptation that arise in the process of evolution of life on Earth.

In the settlement and development of organisms, as well as in the evolution of the biosphere, the most important role was played by global paleogeographic factors (climate, land-sea ratio, atmospheric composition, the presence of areas with nutrient medium and others. The conditions were largely determined by the intensity of volcanic activity and tectonic activity. The connection of continental blocks led to an increase in the seasonality of the climate and to the appearance of glaciation, and the fragmentation of the lithosphere led to a softening of climatic conditions. At the same time, the initial phases of tectonic activity usually corresponded to a climate with the most pronounced seasonality, which was accompanied by glaciation and aridity. This period was followed by intensification of humidization and climate warming, which activated the development of the biosphere. At the same time, for organic life, the supply of gases and nutrients from the bowels of the Earth as a result of volcanic activity was of great importance. For this reason, the development of life and the evolution of the biosphere are largely consistent with the epochs of tectonic activity, when the main events took place in the collision of lithospheric plates and the drift of the continents, and with the existing climatic conditions (Ushakov, Yasamanov, 1984).

The Caledonian Orogeny brought about significant changes in the distribution of sea and land. Mountain building took place in many areas of the planet, in particular, the Scandinavian mountains, the Eastern and Western Sayan Mountains, the ridges of the Baikal and Transbaikalia, etc. arose. The land area increased. Volcanic activity was accompanied by emissions huge amount ash and gases that have changed the properties and composition of the atmosphere. In the Silurian, all platforms experienced a rise. warm seas became shallow, leaving powerful strata of limestones and dolomites.

The climate of this period, characterized by aridity, was warm. The average air temperature at the surface was more than 20°C, exceeding the modern one by 6°C (Bydyko, 1980). The oxygen content in the atmosphere of the Silurian reached 10% of the current level. The formation of the ozone screen continued, which most likely appeared in the Ordovician.

The organic world of the Silurian was much richer than that of the Ordovician. Cartilaginous fish appeared in the seas. Under the protection of the ozone screen, which probably acquired a certain reliability, plants spread over the entire water surface and, together with microscopic animals, formed plankton, which served as a food base or refuge for large organisms. Obviously, plants have received the greatest development in lagoon lakes and coastal swamps with desalinated waters. A life type of plants appeared here, the lower part of which was in the water, and the upper part was in the air. Passive movement in the coastal lowland, associated with sea waves, tides, led to the fact that some plants and animals that abundantly inhabited coastal waters ended up in a periodically flooded and drying zone, in which conditions for amphibian plants differed little from those sea shallows. Having adapted to the existence in this zone, marine plants began to more actively develop the rest of the land.

The first known land plants - kuksonia, united by paleobotanists under common name rhinophytes, still somewhat resembled algae. They had no roots (there were only root-like formations) and leaves. A very simple branching, primitive low (up to 50 cm) stem ended in a spore-bearing process for reproduction. These plants in coastal shallow waters and in wet, low-lying, swampy, and dry places around water basins sometimes formed thickets.

Of the animals, they were inhabited by arthropods, worms and vertebrates, the probable ancestors of which, having settled in the Sea shallow waters and coasts with desalinated water, adapted to life in an oxygen-nitrogen air environment.

The soil substrate, covered with primary terrestrial vegetation, under the influence of bacteria and algae that migrated here, processing organic residues, gradually turned into soil.

The development of land by plants was an outstanding event in the evolution of the organic world and the biosphere.

First of all, the sharply increased primary resources provided the conditions for an accelerated, in comparison with the aquatic environment, process of speciation, devoid of acute competition at the first stages of land settlement. In this process, living organisms have realized their ability to constantly expand their range and develop new habitats (land, air and fresh water). The evolution of the marine fauna in the not so sharply changing iodine environment of the Paleozoic and in the later geological period proceeded very slowly.

The Late Paleozoic included the following periods: Devonian (-100–345 Ma), Carboniferous (345–280 Ma), and Permian (280–235 Ma). This stage was characterized by a wide distribution of land plants and animals. The land has become the main arena for the development of life on Earth.

The ongoing Caledonian orogeny and the early stages of Hercynian folding, together with the movement of lithospheric plates, led to further restructuring of the lithosphere; in the Early and Middle Devonian, a single Pangea already existed, separated from the Siberian microcontinent by the Ural Ocean.

The decrease in the level of the World Ocean was accompanied by the complication of the topography of its bottom. Perhaps at this time the basin was laid Pacific Ocean. The low level of the World Ocean persisted until the next geological period - the Carboniferous.

The increased area of the continents significantly exceeded the area of the sea basins; 70% of the modern oceans were occupied by land.

At the beginning of the Devonian, low (1–2 m) extensive thickets of psilophytes, the evolutionary descendants of rhinophytes, became an integral component of wetlands. The saline habitats were then populated by zosterophyllous, also low-growing plants. For 60 million years, under conditions of a predominantly hot but humid climate, an air environment saturated with carbon dioxide as a result of active volcanic activity, the green cover on swampy shores and freshened shallow waters of warm seas has changed; stunted thickets of primitive plants were replaced by forests of pregymnosperms.

During the Devonian, the first ferns, horsetails and club mosses arose, and the ancient fern (Archaeopteris) flora replaced the psilophyte flora. Along the coasts, in shallow bays and swampy lagoons with a muddy bottom, forests of tree-like ferns appeared. The trunk of ferns at the base reached 2 m, the crown was crowned with snail-twisted young branches (eospermatotheris, archeopteris). The terminal branches of primitive ferns such as ptilophyton were flattened (the first stage in the formation of true leaves). Under the canopy of tree-like ferns, stunted ferns related to them huddled, horsetails became common, and ancient mosses and club mosses (Asteroxylon and Schizopodium) occupied wet places.

The development of the living space of the land continued, but until the middle of the Devonian it was rather slow. In the late Devonian, forests occupied a large part of the land, reducing surface runoff from the continents and thereby reducing erosion. Rainfall runoff from land was replaced by the formation of linear river systems. The input of terrigenous matter into the ocean has sharply decreased. The water in the seas has become more transparent, the area illuminated by the Sun has increased, and the biomass of phytoplankton has increased. In addition to rivers, permanent freshwater reservoirs - lakes - arose on the surface of the continents. The main result of the ongoing processes was that with the formation of vegetation cover on land, the biosphere acquired a powerful resource-reproducing and stabilizing factor.

The reduction in the area of the ocean and changes in its aquatic environment led to some short-term decline in the development of the organic world. In the Devonian seas, the number of trilobites and graptolites drastically decreased, and fish arose and rapidly developed. Some of them (arthrodires) have turned into fast-swimming predators of rather large sizes.

Freshwater lakes and rivers were inhabited by the ancestors of terrestrial vertebrates - lobe-finned fish, which had light and paired fins, from which five-fingered limbs could have arisen.

The ancient representatives of land vertebrates had problems with finding food, reproduction and breathing. The search for food required the improvement of the organs of physical support, which could not but affect the development and strength of the skeleton. However, vertebrates could not yet completely leave the aquatic environment, because their reproductive cells were subjected to drying out under dry conditions.

The difference in the ratio of free oxygen and carbon dioxide in the air and in the aquatic environment contributed to the improvement of the respiratory apparatus.

Such vertebrates, mastering the land, could only be amphibians (amphibians) descended from lobe-finned fish. Body covered with scales with strong bones, four limbs and a long tail ending in a fin, allowed the first inhabitants of land - labyrinthodonts - to lead an aquatic and terrestrial lifestyle. Eyes at the top of the head and sharp teeth enabled these first crocodile-like amphibians to navigate their natural environment.

The increase in aridity and continentality of the climate in the Devonian led to the rapid drying of fresh water bodies, causing mass death their inhabitants. The continental deposits of this time, the ancient red sandstones, contain entire “fish layers”, which made it possible to call the Devonian the “Age of Fishes”.

The end of the Devonian was marked by a new transgression of the sea, as well as an increase in the oceanic climate. The land area gradually decreased, preceded by a new grandiose restructuring of the biosphere.

The Carboniferous, or Carboniferous period, was a period of rapid development of vegetation on all continents and the formation of thick layers of coal in many places on the planet (Ukraine, China, Indonesia, Western Europe, North America). At the beginning of the Carboniferous, the transgression of the sea continued, as a result of which the land area was reduced to 96 million square meters. km, has become 35% less contemporary meaning(149 million sq. km). Under the sea were, in particular, significant areas of Europe. Warm carbonic seas left strata of organogenic and chemogenic limestones.

In the second half of the Carboniferous, the most powerful phase of the Hercynian orogeny, which continued in Perm, led to the emergence of folded mountains of Central Europe, the North Caucasus and Ciscaucasia, the Tien Shan, the Urals, Altai, the Appalachians, the South American Andes, the North American Cordilleras, Mongolia , Canadian Arctic Archipelago, etc.

The activation of mountain-building movements of the earth's crust in the second half of the Carboniferous was accompanied by a prolonged regression of the ocean and an increase in the land area. As a result of the incessant slow movement of lithospheric plates and the Hercynian orogeny, the previously separated parts merged again. With the emergence of new ranges and the retreat of the sea, the relief of the continents became elevated and strongly dissected. The average height of the continents also increased. Along with the existing Gondwana, which united Australia, India, Arabia, South America and Antarctica, no less huge Laurasia was formed on the planet as a result of a significant increase in the area of the North American continent, Europe, the Chinese and Siberian platforms, as well as the formation of land in the North Atlantic. Laurasia was a supercontinent that almost encircled the Arctic Basin. Only Western Siberia remained the seabed. Between Lavrasia and Gondwana is the Mediterranean Ocean Tethys. The oxygen content in the Carboniferous atmosphere remained approximately at the present level. The rapid development of vegetation led to a decrease in the proportion of carbon dioxide in the air to 0.2% in the second half of the Carboniferous. During almost the entire period, a warm, waterlogged climate prevailed. The average air temperature at the beginning of the Carboniferous was 25.6°C (Budyko, 1980), which did not exclude glaciation on almost all continents of the Southern Hemisphere.

In the early Carboniferous, the Euramerian and Angara, or Tunguska, phytogeographic regions separated themselves in Laurasia. In the humid tropical and equatorial climate of the Euramerian region, which included Europe, North America, North Africa, the Caucasus, Central Kazakhstan, Central Asia, China and Southeast Asia, dominated by multi-tiered forests of tall (up to 30 m) plasgns with a branched crown and psaronius ferns with large pinnate leaves. Horsetail calamites and cuneiformes also gave originality to these forests. If the height of calamites reached 10, less often 20 m, then the cuneiforms had decumbent or creeping stems several meters long. In a warm and constantly humid climate, wood did not have growth rings of radial growth. Green algae-carbon-forming algae abounded in fresh waters. The gloomy world of forest swamps was supplemented by stegocephals and amphibians; reptiles were still rare. Mayflies and dragonflies soared in the air, which reached gigantic sizes (wingspan up to 70 cm), arachnids were also widespread. In general, the flowering of insects is characteristic of the Carboniferous.

To the north, in the Angarsk region (Siberia, East Kazakhstan, Mongolia), ferns and cordaites replaced the dominant lycopsids in the Middle and Late Carboniferous. The cordaite "taiga" was characterized by tall (more than 30 m) trees with a trunk with growth rings and a plexus of roots that went into marshy soil. Their branches ended in long (up to 1 m) linear leaves. Cordaite "taiga" has conquered flat areas with a continental climate and seasonal temperature changes.

In the Gondwana region with a moderately warm and humid climate, a glossopteris, or Gondwana, small-leaved flora, devoid of tree ferns, developed. By the end of the Carboniferous, in connection with continental glaciation, the woody vegetation of Gondwana was replaced by shrubs and grasses. In changing climatic conditions, seed ferns (pteridosperms) and the first gymnosperms, cycads and bennettites, which, like cordaites, were more adapted to the change of seasons, acquired an evolutionary advantage. Seeds stocked nutrients and protected by a shell from the adverse effects natural conditions, performed the task of reproduction and distribution of plants much more successfully. It should be noted that cycads have survived to this day. it ordinary plants tropical and sub rainforest.

The fauna of the Carboniferous was marked by the appearance of the first reptiles (reptiles), which, in terms of their biological organization, were much better adapted to living on land than their amphibian ancestors. In the history of vertebrate development, reptiles were the first animals to reproduce by laying eggs on land, breathing only with lungs. Their skin was covered with scales or scutes.

Despite the progressive development of integument, respiratory and circulatory organs, reptiles did not provide themselves with a warm-blooded body, and their body temperature, like that of amphibians, depended on temperature. environment. This circumstance later played a major role in their evolution. The first reptiles - cotylosaurs - were massive animals ranging in size from several tens of centimeters to several meters, moving on thick five-fingered limbs. More mobile forms of reptiles originated from them, while the cranial shell inherited by the latter was reduced, the limbs were lengthened, and the skeleton became lighter.

Permian period

The Hercynian orogeny ended in the middle of the next geological period, the Permian. In Perm, a single Pangea continued to exist, stretching from the South to the North Pole. Compression of the Hercynian Ural-Appalachian belt and further movement of lithospheric plates led to the formation of mountain systems. The high mountain systems created by the Hercynian orogeny and, mainly, the gigantic land area contributed to the loss of heat from the biosphere. The average air temperature of the Earth dropped by 3–4 °C, but remained 6–7 °C higher than the current one. Low temperatures indicated the ongoing planetary cooling associated with the Upper Paleozoic (Permo-Carboniferous) glaciation of Gondwana. In the Northern Hemisphere, glaciation probably had a local, mountainous manifestation. Chemical composition, the structure and circulation of the atmosphere approached modern ones; in general, the Permian climate was characterized by pronounced zoning and increasing aridity. The belt of humid tropical climate, confined to the Tethys Ocean, was located inside the belts of hot and dry climate, with which the deposition of salts and red-colored rocks was associated. To the north and south were humid temperate zones with coal accumulation. Subpolar cold regions are distinctly isolated.

Reducing the evaporative ocean surface by more than 30 million square meters. km, as well as the withdrawal of water for the formation of continental ice sheets led to a general aridization of the climate and the development of desert and semi-desert landscapes. The increase in land area increased the role of land plants in the evolution of the biosphere. In the middle of the Permian, a powerful flow of the glossopteris flora of Gondwana formed, rushing through Hindustan and tropical Africa to Europe and Asia. The East European Platform, as well as other land areas in the Northern Hemisphere, under the conditions of climate aridization, turned into an arena of evolutionary struggle between the dying Euramerian and viable Gondwanan floras. A variety of ferns and preserved sigillaria club mosses formed more or less dense thickets on the coasts of shallow lagoons and swampy areas. Cordaite "taiga" flourished in the north of Laurasia. The richness of vegetation favored coal accumulation.

By the end of the Permian, some previously widespread plant groups, primarily tree clubs and cordaites, became extinct. More and more they were replaced by real gymnosperms - conifers, ginkgos, bennettites and cycads. An essential role in the formation of vegetation cover in conditions temperate climate moss played.

The rich and diverse fauna of the seas underwent significant changes by the end of the Permian. The reduction of the aquatic environment led to the great extinction of the marine fauna. Many groups of sea lilies and hedgehogs, trilobites, rugosas, a number of cartilaginous, crossopterygian and lungfishes have become extinct.

Terrestrial vertebrates were represented by amphibians and reptiles. The stegocephals that prevailed among the amphibians, for the most part, died out at the end of Perm. Along with primitive reptiles - cotylosaurs, reptiles were widely used.

The Paleozoic era is a geological period that began 541 million years ago and ended 252 million years ago.

It is the first in the Phanerozoic eon. It was preceded by the Neoproterozoic, and will be followed by the Mesozoic era.

Periods of the Paleozoic era

The era is quite long, so scientists decided to break it into more convenient segments - periods based on stratigraphy data.

There are only six of them:

Cambrian
ordovician,
silurian,
Devonian,
carbon,
Permian.

Processes of the Paleozoic era

In the Paleozoic era, large and small changes occurred in the appearance of the earth, its development, the formation of the flora and fauna.

Palaeozoic. Cambrian period photo

There was an intensive formation of mountains and mountain ranges, the activity of existing volcanoes was noted, cooling and heat changed all the time, the level of the seas and oceans increased and decreased.

Characteristics of the Paleozoic era

The beginning of the Paleozoic era was marked by the Cambrian explosion or a sharp increase in the number of living beings. Life took place mainly in the seas and oceans and was just beginning to move to land. Then there was one supercontinent - Gondwana.

Palaeozoic. Ordovician period photo

By the end of the Paleozoic, there were significant changes in the movement of tectonic plates. Several continents joined together to form a new supercontinent - Pangea.

Palaeozoic. Silurian period photo

The era ended with the extinction of almost all living things. It is one of the 5 great extinctions on the planet. During the Permian period, up to 96% of the living organisms of the world's oceans and up to 71% of terrestrial life died out.

Life in the Paleozoic era

Life was too varied. Climates changed each other, new forms of life developed, for the first time life "moved" to land, and insects mastered not only the water and earth, but also the air environment, having learned to fly.

Flora in the Paleozoic era developed rapidly, as did the fauna.

Plants of the Paleozoic era

During the first two periods of the Paleozoic era vegetable world was represented mainly by algae. During the Silurian period, the first spore plants appear, and at the beginning of the Delurian there are already many simple plants - rhinophytes. By the middle of this period, vegetation develops.

Palaeozoic. Devonian period photo

The first lycopsids, great-ferns, arthropods, progymnosperms, and gymnosperms appeared. Soil cover develops. Carboniferous marked the appearance of horsetail-like, tree-like plantains, ferns and ferns, cordaites. The Carboniferous flora eventually formed a thick layer of coal, which is mined to this day.

Animals of the Paleozoic Era

Throughout the Paleozoic, all kinds of animals appeared and formed on the planet, with the exception of birds and all mammals. At the beginning of the Cambrian, an incredibly large number of creatures with a hard skeleton appeared: acritarchs, archaeocyates, brachiopods, gastropods, bivalves, bryozoans, stromatoporoids, chiolites, chiolithelminths.

Palaeozoic. carbonic period photo

Trilobites became common - the oldest form of arthropods. There were many invertebrate graptolites, cephalopods. In the Devonian period, gonyptites appeared - a more complex form of invertebrates. And in the Late Paleozoic, foraminifera formed.

Land in the Paleozoic was inhabited by centipedes, spiders, ticks, scorpions and various insects. In the Cambrian, gastropods appeared that could breathe with their lungs. Some flying insects are also known. Aromorphoses of the Paleozoic Era During the Paleozoic, significant changes occurred in the formation of life on the planet.

Palaeozoic. permian period photo

In the Cambrian, animals had a predominantly calcareous or phosphate skeleton, predators predominated, and moving organisms began to develop. Animals are still evolving. Silur marked the appearance of the first arthropods, a new order of invertebrates - echinoderms and vertebrates. Protozoan land plants also evolved.

The Devonian period was the beginning of the reign of fish. Some animals develop lungs - amphibians appear. At this time, mosses, club mosses, horsetails and ferns developed. In the Carboniferous, insects learned to fly, gymnosperms begin to spread.

Palaeozoic. photo development periods

By the end of the Permian period, the pulmonary system of some animals became much more complicated, a new type of skin appeared - scales.

The climate of the Paleozoic era

At the beginning of the period under review, the Earth was warm. Predominated over all land areas tropical climate, the temperature in the seas and oceans did not fall below 20 degrees Celsius. In the next two periods, the climate changes significantly.

There are five climatic zones:

equatorial,
tropical,
subtropical,
moderate,
nival.

By the end of the Ordovician, the cold began. The temperature in the subtropics dropped by 10-15 degrees, and in the tropics by 3-5 degrees. In the Silurian, the climate returned to normal - it became warmer. The increase in vegetation led to abundant photosynthesis. The formation of Pangea led to the fact that for some time there was practically no precipitation at all. The climate was dry and temperate. But soon it started to get colder.

In the Late Carboniferous and Early Permian, ice covered the entire northern part of Pangea. The end of the era brought warmth, the belt of the tropics and the equatorial zone expanded. The water temperature has risen significantly.

There is some evidence that higher land plants already existed in the Cambrian and Ordovician, but scientists still have not come to a consensus on this, so this is just an unconfirmed theory.
The sizes of Paleozoic insects were not quite standard. So the wingspan of an ordinary dragonfly was a meter! Millipedes reached 2 meters! It is believed that insects reached such sizes due to the abundance of oxygen in the air. In the Late Carboniferous, the formation of different climatic zones took place, which are known to this day.
The Paleozoic era brought many changes to the planet. Climates, continents changed, mountains and seas formed. This is the time of development of new forms of life. Some of them still exist today, but on a much smaller scale and in greater variety.

They lived in the seas.

Some animals led sedentary life, others went with the flow. Bivalves, gastropods, annelids, trilobites were widely distributed and actively moved. The first representatives of vertebrates appeared - armored fish, which did not have a jaw. Shellfish are considered distant ancestors of modern cyclostomes, lampreys, hagfish.

Remains of protozoa, sponges, coelenterates, crustaceans, blue-green and green algae, as well as spores of plants that grew on land were found in mountain deposits.

AT Ordovician period the areas of the seas have expanded, the variety of green, brown, red algae, cephalopods and gastropods. The formation of coral reefs is increasing, the diversity of sponges is decreasing, as well as some bivalves.

Climate

AT Silurian period mountain building processes are intensifying, the land area is increasing. The climate becomes relatively dry and warm. Powerful volcanic processes took place in Asia. Fossilized prints of coelenterates and a short psilophyte have been found in mountain deposits.

Animals

Climate

AT Devonian the area of the seas continues to decrease and the land to increase and separate. The climate becomes temperate. A significant part of the land turns into deserts and semi-deserts.

Animals

The conditions of the Permian period were extremely unfavorable for amphibians. Most of them died out, this event was called the "Mass Permian extinction" . Smaller representatives of amphibians took refuge in swamps and shallows. The struggle for existence and natural selection in a dry and more or less cold climate caused changes in certain groups of amphibians, from which reptiles then originated.

Mass Permian extinction

A major marine extinction occurred at the Paleozoic–Mesozoic boundary. Its causes can be associated with the success of terrestrial vegetation in terms of soil fixation. Just shortly before that, drought-resistant conifers appeared, which for the first time were able to populate the interior of the continents and reduce their erosion.

Page 1 of 7

Palaeozoic occupies a time interval of 289 million years. The third era of the development of the Earth lasted from 540-252 million years ago and followed the Proterozoic (Proterozoic era). The Paleozoic era is divided into 6 geological periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous (Carboniferous) and Permian (Permian).

Let's take a closer look periods of the Paleozoic era.

Cambrian. The first period of the Paleozoic era lasts 56 million years. At this time, there is an active formation of mountain ranges. Only bacteria and algae can still live on earth. But in sea depths the diversity of living organisms. Trilobites appear - invertebrate arthropods, similar to modern representatives of the crayfish family. In reservoirs, the amount of magnesium and calcium increases. Mineral salts contained in the earth begin to enter the seas in large quantities. This makes it possible for animals living in water to evolve - to create a solid skeleton.

Ordovician. The second erathem of the Paleozoic era occupies a time interval of 42 million years. This period characterized by the flourishing of life on the planet. The main types of marine inhabitants are formed. The first armored jawless fish, starfish and lilies, huge scorpions appear. At the end of the Ordovician period, the first representatives of vertebrates appear.

Silurus. The Silurian following the Ordovician lasts 24 Ma. This is the era of land conquest by the ancient ancestors of spiders, centipedes and scorpions. Armored jawed fish appear. At the beginning of the Silurian, more than half of the existing living organisms die out. In the northern part of the Earth, the Laurentia continent is being formed. Gondwana is divided into 2 parts by a newly formed sea bay. The land gradually goes under water - this leads to the formation of sedimentary rocks. At the end of the Silurian period, the stage of Caledonian development ends. The mountain ranges of Scotland and Greenland begin to actively form; most of Cordillera. On the site of modern Siberia, the Angarida continent is formed.

Devonian. The Devonian period lasts 61 million years. The first sharks, insects and amphibians appear. The land is getting greener. Now ferns and psilophytes live on it. The remains of dying plants form layers of coal. On the territory of modern England, the first rocks are formed. The continents of Laurentia, Baltica and Avalonia collide and form a single continent. Gondwana is shifting from south to north. Huge deserts form within the continents. In the middle of the Devonian, the polar glaciers begin to melt. As a result, the ocean level rises - this contributes to the formation of coral reefs off the coast of Laurentia.

Carboniferous period (Carboniferous). The fifth period of the Paleozoic era has another name - carbon. Its duration is 60 million years. This is the time of formation of the main coal deposits. At the beginning of the Carboniferous, ferns, lepidodendrons, club mosses, cordaites cover the Earth. By the end of the erathema, coniferous forests appear. Higher insects are born - cockroaches and dragonflies. The first reptiles and squid ancestors appear - belemnites. The main continents of that time were Laurasia and Gondwana. Insects begin to master the air. Dragonflies fly first. Then butterflies, beetles and grasshoppers rise into the air. The first mushrooms, moss and lichens appear in the forests. By studying the Carboniferous flora, one can observe the evolutionary process of plants.

Permian period (Permian). The final period of the Paleozoic era lasts about 46 million years. It begins with the next glaciation in the south of the planet. As the mainland Gondwana moves from south to north, the ice caps begin to melt. In Laurasia, a very hot climate, which leads to the formation of giant desert zones. At the border of the Carboniferous and the Permian, bacteria begin to process wood. Thanks to this significant event, another oxygen catastrophe, threatening all living things, never happened. Vertebrates dominate the earth. The ancestors of mammals appear - the animal-like lizards of therapsids. The seas are dominated by bony fish. By the end of the era, trilobites, crustaceans and some types of corals are dying out. There are fewer lepidodendrons and sigillaria. Language ferns, coniferous and gingko trees, cycads (ancestors of palms), cordaites (ancestors of pines) develop. Living organisms begin to settle in arid regions. Best acclimatization occurs in reptiles.

The climate of the Paleozoic era

The climate of the Paleozoic era most similar to the climate modern world. At the beginning of the era, a warm climate with low climatic zoning prevails. At the end of the Paleozoic, aridity develops and a sharp zonality is formed.

In the first half Cambrian period nitrogen content prevailed in the atmosphere, the level of carbon dioxide was not higher than 0.3%, and the amount of oxygen gradually increased. On the continents, the weather was hot and humid.

In the second half of the Ordovician, the planet became very cold. During the same period, zones with tropical, subtropical, temperate and equatorial climate. In the subtropics, the average air temperature decreased by 15, in the tropics - by 5 degrees. Mountain ranges of Gondwana, located on south pole covered by glaciers.

By the beginning of the Carboniferous period, tropical and equatorial types of climate reigned on Earth.

The development of plant life on land contributed to the active process of photosynthesis with an increased decrease in the level of carbon dioxide in the atmosphere and an increase in the oxygen content. The formation of the Pangea continent led to the cessation of precipitation and the limitation of the connection between the seas of the equator and the polar ones. As a result of these events, a strong cooling set in with a pronounced temperature difference at the equator and the poles.

During the Paleozoic era 2 tropical, 2 subtropical, 2 temperate and 1 equatorial climatic zones have formed on the planet. By the end of the Paleozoic era, the cool climate was again replaced by a warm one.

Animals of the Paleozoic Era

In the Cambrian era of the Paleozoic era, trilobites, invertebrate, arthropod, crustacean creatures, dominate the oceans and seas. Their bodies were protected by strong chitinous shells, divided into about 40 parts. Some individuals reached a length of more than 50 cm. Trilobites fed sea plants and the remains of other animals. Another species of multicellular animals of the Cambrian, which became extinct by the beginning of the Ordovician, are archaeocyates. These creatures are like the coral reefs of our time.

In the Silurian period, trilobites, mollusks, brachiopods, sea lilies, starfish and sea urchins. A distinctive feature of Silurian bivalve mollusks was the bending of their valves in different directions. In most of the gastropods, the shells turned to the right side. Their cephalopod counterparts had smooth horny shells. At the same time, the first vertebrate creatures appear - fish.

In the Carboniferous period, representatives of marine inhabitants - foraminifers and schwagerins - became widespread. Many deposits of limestone are formed from their shells. Sea lilies and hedgehogs develop, produktus - representatives of brachiopod mollusks. Their sizes reached 30 cm. Along the edge there were long shoots, with the help of which the produktus were attached to underwater plants.

During the Devonian, the seas were dominated by placoderms - fish with strong jaws and a hard shell that protected the head and front of the torso. These are the biggest predatory fish that time. Dunkleosteus - a variety of placoderms - reached a length of up to 4 meters and in structure resembled cladoselachia - the first sharks. In the reservoirs of this time period, shellless fish were found, similar to modern ones. They are divided into 2 groups: cartilage and bone. Cartilaginous fish are the forerunners of sharks and rays of our time. Their mouths were full of sharp teeth, and their bodies were covered with tough scales. Bony fish were small in size, with thin scales and movable fins. According to scientists, four-legged vertebrates originated from lobe-finned bony fish. In the Devonian period, the first ammonites appear - predatory mollusks with a spiral shell. They had an upper shell with partitions. The ammonites filled the empty space between these partitions with water and gas. Due to this, their floating properties changed for the better.

By the end of the Paleozoic era, the flowering of reptiles begins. Reptiles have adapted faster than any other living creatures to a changing climate. Found fossilized skeletons allow you to recreate the appearance of animals completely. Moschops was one of the largest herbivores of that time. The reptile had a long tail, a large skull, a barrel-like body. Its dimensions reach up to 4 meters in length. Anthosaurus is a predator similar in size to Moschops.

Plants of the Paleozoic era

The first plants that filled the land were psilophytes. Later, other types of vascular species originated from them - club mosses, horsetails, ferns. The humid climate of the Carboniferous gave rise to the prototypes of tropical forests. Lepidodendrons and sigillaria, calamites and cordaites, ferns grew in them.

By the middle of the Permian period, the climate becomes dry. In this regard, moisture-loving ferns, calamites and tree-like clubs disappear.

In the Ordovician, sea lilies develop. They were attached to the bottom with a stem consisting of ring-shaped parts. Around the mouth they had movable rays, with which the lilies caught food in the water. Often sea lilies formed dense thickets.

In the middle of the Paleozoic era, arthropod plants arose, which are divided into 2 groups - cuneiform and calamites. The first group is plants that live in water. They had a long uneven stem with leaves. Spores formed in the kidneys. Cuneiformes kept on the surface of the water with the help of branched stems. Calamites are tree-like plants that form swamp forests. In height reach 30 meters.

Minerals of the Paleozoic era

The Paleozoic era is rich in minerals. During the Carboniferous, the remains of animals and dying plants formed huge deposits of coal. In the Paleozoic era, deposits of oil and gas, rock and mineral salt, copper, manganese and iron ores, limestone, phosphorites and gypsum were formed.

Paleozoic era and its periods will be discussed in more detail in the following lectures.

Paleozoic era: Cambrian period (from 540 to 488 million years ago)

This period began with an astonishing evolutionary explosion, during which representatives of most of the major groups of animals known for the first time appeared on Earth. modern science. The boundary between the Precambrian and Cambrian runs along rocks, which suddenly reveal a surprising variety of animal fossils with mineral skeletons - the result of " Cambrian Explosion"life forms.

In the Cambrian period, large areas of land were occupied by water, and the first supercontinent Pangea was divided into two continents - northern (Laurasia) and southern (Gondwana). Significant erosion of the land is observed, volcanic activity was very intense, the continents either fell or rose, resulting in the formation of shoals and shallow seas, which sometimes dried up for several million years, and then were again filled with water. At this time, the oldest mountains appeared in Western Europe(Scandinavian) and in Central Asia(Sayans).

All animals and plants lived in the sea, however, the intertidal zone was already inhabited by microscopic algae, which formed terrestrial algal crusts. It is believed that the first lichens and terrestrial fungi began to appear at this time. Animal world of that time, first discovered in 1909 in the mountains of Canada by C. Walcott, was represented mainly by benthic organisms, such as archaeocyates (analogues of corals), sponges, various echinoderms (starfish, sea urchins, sea cucumbers etc.), worms, arthropods (various trilobites, horseshoe crabs). The latter were the most common form of living creatures of that time (approximately 60% of all animal species were trilobites, which consisted of three parts - head, body and tail). All of them died out by the end of the Permian period, of horseshoe crabs, only representatives of one family have survived to this day. Approximately 30% of the Cambrian species were brachiopods - marine animals with a bivalve shell, similar to molluscs. From trilobites that switched to predation, crustaceans up to 2 m long appeared. At the end of the Cambrian period, cephalopods appeared, including the nautilus genus that has survived to this day, and from echinoderms, primitive chordates (tunicates and non-cranial). The appearance of a chord, which gave the body rigidity, was important event in the history of the development of life.

Paleozoic era: Ordovician and Silurian periods (from 488 to 416 million years ago)

At the beginning of the Ordovician period, most of the southern hemisphere was still occupied by the great continent of Gondwana, while other large land masses were concentrated closer to the equator. Europe and North America (Laurentia) were pushed further apart by the expanding Iapetus Ocean. First, this ocean reached a width of about 2000 km, then began to narrow again as the land masses that make up Europe, North America and Greenland began to gradually converge until they finally merged into a single whole. During the Silurian period, Siberia "sailed" to Europe (the Kazakh uplands formed), Africa collided with southern part North America, and as a result, a new giant supercontinent Laurasia was born.

After the Cambrian, evolution was characterized not by the emergence of completely new types of animals, but by the development of existing ones. In the Ordovician, the most severe land flooding in the history of the earth took place; as a result, most of it was covered with huge swamps; arthropods and cephalopods were common in the seas. The first jawless vertebrates appear (for example, the current cyclostomes - lampreys). These were benthic forms feeding on organic remains. Their body was covered with shields that protected them from crustaceans, but they did not yet have an internal skeleton.

Approximately 440 million years ago, two significant events occurred at once: the emergence of plants and invertebrates on land. In the Silurian, there was a significant uplift of land and a retreat of ocean waters. At this time, along the marshy shores of reservoirs, in tidal zones lichens and the first land plants appeared, resembling algae - psilophytes. As an adaptation to life on land, the epidermis with stomata, the central conducting system, and mechanical tissue appear. Spores are formed with a thick shell, protecting from drying out. Subsequently, the evolution of plants went in two directions: bryophytes and higher spores, as well as seed ones.

The emergence of invertebrates on land was due to the search for new habitats, the absence of competitors and predators. The first terrestrial invertebrates were tardigrades (which tolerate desiccation well), annelids, and then centipedes, scorpions, and arachnids. These groups originated from trilobites often stranded on the shallows at low tide. On fig. 3 shows the main representatives of the early Paleozoic animals.

Rice. 3. Early Paleozoic: 1-archaeocyates, 2,3-intestinal (2-four-beam corals, 3-jellyfish), 4-trilobites, 5,6-molluscs (5-cephalopod, 6-gastropod), 7-brachiopods, 8, 9-echinoderms (9-sea lilies), 10-graptolites (semi-chordates), 11-jawless fish-like.