History of the geological development of the earth. Geological time, eras and periods in the history of planet earth

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

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

Stages of Earth's development

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

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

There are 4 eons in total. Each of them, in turn, is divided into eras of the Earth, and those are divided into periods. From this it is clear that there is a strict gradation of large time intervals, and the geological development of the planet is taken as the basis.

Katarhey

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

Archaea

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

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

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

Mesoarchean(3.2-2.8 billion years) lasted 400 million years. The most remarkable thing about it was the existence of cyanobacteria. They are capable of photosynthesis and produce oxygen. The formation of the supercontinent has completed. By the end of the era it had split. There was also a huge asteroid impact. The crater from it still exists in Greenland.

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

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

Proterozoic

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

Siderius notable in the first place oxygen catastrophe. It happened 2.4 billion years ago. Characterized by a dramatic change in the Earth's atmosphere. Free oxygen appeared in it in huge quantities. Before this, the atmosphere was dominated by carbon dioxide, hydrogen sulfide, methane and ammonia. But as a result of photosynthesis and the extinction of volcanic activity at the bottom of the oceans, oxygen filled the entire atmosphere.

Oxygen photosynthesis is characteristic of cyanobacteria, which proliferated on Earth 2.7 billion years ago. Before this, archaebacteria dominated. They did not produce oxygen during photosynthesis. In addition, oxygen was initially consumed in the oxidation of rocks. It accumulated in large quantities only in biocenoses or bacterial mats.

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

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

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

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

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

During the time of Kalimium, the supercontinent Colombia broke up. And during the Exatian era, red multicellular algae appeared. This is indicated by a fossil find on the Canadian island of Somerset. Its age is 1.2 billion years. A new supercontinent, Rodinia, formed in Stenium. It arose 1.1 billion years ago and disintegrated 750 million years ago. Thus, by the end of the Mesoproterozoic there was 1 supercontinent and 1 ocean on Earth, called Mirovia.

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

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

Life on Earth originated in the ocean

Phanerozoic

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

Cambrian considered to be the lifespan of trilobites. These are marine animals similar to crustaceans. Along with them, jellyfish, sponges and worms lived in the seas. Such an abundance of living beings is called Cambrian explosion. That is, there was nothing like this before and suddenly it suddenly appeared. Most likely, it was in the Cambrian that mineral skeletons began to emerge. Previously, the living world had soft bodies. Naturally, they were not preserved. Therefore, complex multicellular organisms of more ancient eras cannot be detected.

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

Plants began to colonize land during the Silurian period

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

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

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

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

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

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

This is what nature was like in the early Cretaceous period

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

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

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

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

Surface of the Earth 65 million years ago

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

During the Cenozoic, the continents diverged. Each of them formed its own unique flora and fauna. The diversity of marine, flying and terrestrial animals has increased significantly compared to the Paleozoic. They became much more advanced, and mammals took a dominant position on the planet. Higher angiosperms appeared in the plant world. This is the presence of a flower and an ovule. Cereal crops also appeared.

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

Notable for the Pleistocene and Ice Ages. For as long as 2 million years, very cold and warm periods of time alternated on Earth. Over the past 800 thousand years, there have been 8 ice ages with an average duration of 40 thousand years. During cold times, glaciers advanced on the continents, and retreated during interglacial periods. At the same time, the level of the World Ocean rose. About 12 thousand years ago, already in the Holocene, the next ice age ended. The climate became warm and humid. Thanks to this, humanity spread throughout the planet.

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

The article was written by Vitaly Shipunov

Sedimentary rocks, methods of formation, classification

Sedimentary rocks accumulate on the earth's surface, occupying over 75% of the land surface area. More than 95% of their volume accumulated in marine conditions. Most sedimentary rocks are characterized by a layered texture, reflecting the periodicity of sedimentation. The nature of layering depends on the specific conditions of the process, and the primary one is the dynamics of the environment. Thus, in stagnant water, horizontal layering occurs, and in a river flow, inclined layering occurs. Another characteristic textural feature is porosity. The texture of sedimentary rocks is most often porous and compact (non-porous). Depending on the pore size, porosity is divided into coarse, coarse, fine and fine.

In the case of an accumulation of more or less identical particles, the structure is called uniform-grained; otherwise, it is called heterogranular. According to the shape of the particles, rocks have a rounded and unrounded structure.

Chemical rocks are characterized by oolitic (grains are spherical), acicular, fibrous, leafy and granular structures. Rocks of organic origin, consisting of well-preserved shells or plants, have a biomorphic structure.

If sedimentary rocks are an accumulation of individual particles not connected to each other, they are called granular. When individual larger particles are held together by a fine-grained material called cement, the rocks are called cemented and are characterized by a compact texture. Cementation of rocks can occur simultaneously with their formation, as well as after, as a result of the precipitation of various salts from solutions circulating through the pores. Based on their composition, they distinguish between clay, bitumen, lime, ferruginous, siliceous and other cements. The nature of cement largely determines the density and strength of cemented rocks. Rocks with clay cement are considered the weakest, while rocks with siliceous cement are the strongest.

Based on their origin, sedimentary rocks can be divided into five groups.

Clastic (clastic) rocks are formed as a result of mechanical destruction of any other rocks. They are classified according to three criteria. 1. By size (diameter) of fragments: coarse clastic (psephites), medium clastic (psammites) and fine clastic (silts). 2. According to the shape of the fragments: angular (crushed stone) and rounded (pebbles). 3. According to the presence of cement: loose (sand) and cemented (sandstone).

Clay rocks (pelites) consist of tiny particles, the diameter of which is less than 0.01 mm. Most of them arise due to chemical weathering processes. The accumulation of clays is associated with the precipitation of matter from colloidal solutions, due to which the clays are characterized by thin horizontal layering. When clays dehydrate, dense mudstones that do not soak in water appear.

Chemogenic rocks arise when a substance crystallizes from supersaturated aqueous solutions. For the most part, chemogenic rocks are monomineral: they consist of minerals of the classes of carbonates (chemogenic limestones), sulfates (gypsum and anhydrite), halides (rock and potassium salts), etc. Chemogenic rocks are characterized by a fully crystalline (crystalline-granular) structure: from coarse to fine crystalline , and even cryptocrystalline. Their texture is both layered and homogeneously massive.

Organogenic rocks are formed due to the accumulation of waste products of organisms: primarily marine and, to a lesser extent, freshwater invertebrates. Some organogenic rocks arise from the accumulation of plant remains (peat). In terms of mineral composition, carbonate rocks (limestone-shell rock, chalk) predominate; siliceous rocks (diatomite) and other organogenic rocks are less common. Among the characteristic structures it is necessary to name biomorphic (the rock consists of undisturbed skeletons), detritus (the rock consists of crushed skeletons), biomorphic - detritus (the rock is composed of both intact and destroyed skeletons). The texture of organogenic rocks is layered and porous.

Sedimentary rocks of mixed origin have a complex composition and arise under the combined influence of different processes. Among the mixed species, marl and opoka should be mentioned.

The history of the Earth is divided into large periods of time called geological eras; eras (with the exception of the most ancient) are divided into geological periods, and those, in turn, into epochs. The boundaries between these divisions correspond to various kinds of changes of a geological and biological (paleontological) nature: increased volcanism and mountain-building processes; uplifts or subsidences of significant areas of the continental crust, leading to corresponding invasions or retreats of the sea (marine transgressions and regressions); significant changes in fauna and flora, etc.

The geological history of the Earth is divided into large intervals - eras, eras - into periods, periods - into centuries. The division into eras, periods and centuries is, of course, relative, because there were no sharp distinctions between these divisions. But still, it was at the turn of neighboring eras and periods that significant geological transformations took place - mountain-building processes, redistribution of land and sea, climate change, etc. In addition, each division was characterized by the qualitative originality of flora and fauna.

The deposits of the most ancient Archeozoic and Proterozoic eras contain extremely few fossil remains of organisms; on this basis, the Archeozoic and Proterozoic are often combined under the name “cryptozoic” (the stage of hidden life), in contrast to the three subsequent eras - the Paleozoic, Mesozoic and Cenozoic, united as the “Phanerozoic” (the stage of obvious, observable life).

Geological eras of Earth's history:

· catarchaea (from the formation of the Earth 5 billion years ago to the origin of life)

An era when there was a lifeless Earth, shrouded in an atmosphere devoid of oxygen, poisonous to living beings; Volcanic eruptions thundered, lightning flashed, hard ultraviolet radiation penetrated the atmosphere and upper layers of water. Under the influence of these phenomena, the first organic compounds begin to be synthesized from the mixture of hydrogen sulfide, ammonia, and carbon monoxide vapors that enveloped the Earth, and properties characteristic of life appear.

Archaean, ancient era (3.8 billion - 2.6 billion years)

The primary crust, formed as a result of the cooling of the Earth, was continuously destroyed by steam and gas, which were released by the hot substance. Lava erupted by millions of volcanoes solidified on the surface, forming primary mountains and plateaus, continents and oceanic depressions. The powerful, dense atmosphere also cooled, resulting in heavy rainfall. On the hot earth's surface they instantly turned into steam. Solid clouds enveloped the Earth, preventing the passage of the sun's rays, warming its surface. The solid crust cooled, the oceanic depressions filled with water. The primary ocean, rivers, and atmosphere destroyed the primary mountains and continents, forming the first sedimentary rocks. Now they are hard and dense. The formation of many minerals is associated with them: building stone, mica, nickel ore, kaolin, gold, molybdenum, copper, cobalt, radioactive minerals, iron. In the Archean era, various chemical reactions between salts, alkalis and acids took place in the warm waters of the primary ocean. They were favored by solar radiation, a dense atmosphere, and ionization of water caused by huge lightning discharges. At the end of the Archean era, lumps of protein matter appeared in the seas, marking the beginning of all life on Earth.

Proterozoic (2.6 billion - 570 million years)

The coal-like material shungite was found in Proterozoic deposits. This indicates the appearance in the Proterozoic era of plants, from the remains of which coal was formed. Marble deposits suggest that animals with calcareous shells lived in the Proterozoic. Over time, the limestones formed from the deposits of these shells turned into marble. Proterozoic rocks contain deposits of the sea, land, rivers, mountains, deserts and glaciers. Consequently, the climate of the Proterozoic was quite diverse. The marine sediments are covered by volcanic sediments, which are also overlain by marine sediments. Periods of quiet development of the Proterozoic earth's crust were replaced by violent mountain-building processes. Many minerals are associated with Proterozoic deposits: iron ores, marble, graphite, nickel ore, piezoquartz, kaolin, gold, mica, talc, molybdenum, copper, bismuth, tungsten, cobalt, radioactive minerals, precious stones. At the end of the Proterozoic, thanks to mountain-building processes, mountains arose in place of the sea, and sedimentary deposits metamorphosed. The end of the Proterozoic is sometimes called the “age of jellyfish” - representatives of the coelenterates that were very common at that time.

· Paleozoic (570 million - 230 million years) with the following periods: Cambrian (570 million - 500 million years); Ordovician (500 million - 440 million years); Silurian (440 million - 410 million years); Devonian (410 million - 350 million years); Carboniferous (350 million - 285 million years); Permian (285 million - 230 million years);

The Paleozoic era of the Earth's development is divided into two large stages: the Early Paleozoic, which began in the Late Riphean and Vendian and ended in the Silurian period, and the Late Paleozoic, which included the Devonian, Carboniferous and Permian periods. Each of them in the mobile belts ended with folding - Caledonian and Hercynian, as a result of which extended mountain-folded areas and systems were formed, attached to stable platforms and “fused” with them. The mountain-building period that began at the end of the Silurian changed the climate and the living conditions of organisms. As a result of the rise of land and the reduction of seas, the Devonian climate was more continental than in the Silurian. In the Devonian, desert and semi-desert regions appeared; The first forests of giant ferns, horsetails and club mosses appear on land. New groups of animals begin to conquer land. The end of the Carboniferous period saw the appearance of the first reptiles - completely terrestrial representatives of vertebrates. They achieved significant diversity in the Permian due to the arid climate and cooling.

· Mesozoic (230 million - 67 million years) with the following periods: Triassic (230 million - 195 million years); Jurassic (195 million - 137 million years); Cretaceous (137 million - 67 million years)

The Mesozoic is rightly called the era of reptiles. Their heyday and extinction occur precisely in this era. In the Mesozoic, the climate becomes more arid. Many land organisms, in which certain stages of life are associated with water, are dying out. Instead, terrestrial forms begin to predominate. In the Triassic, gymnosperms reached strong development among plants, and reptiles among animals. Herbivorous and carnivorous dinosaurs appeared in the Triassic. Marine reptiles are very diverse in this era. In the Jurassic, reptiles began to master the air environment. Flying lizards survived until the end of the Cretaceous. In the Jurassic, birds also evolved from reptiles. On land in the Jurassic, giant herbivorous dinosaurs are found. In the second half of the Cretaceous, marsupials and placental mammals arose. The acquisition of viviparity and warm-bloodedness were the aromorphoses that ensured the progress of mammals.

Cenozoic (67 million - up to our time) with the following periods and centuries:

– Paleogene (67 million - 27 million years): Paleocene (67-54 million years), Eocene (54-38 million years), Oligocene (38-27 million years);

– Neogene (27 million - 3 million years): Miocene (27-8 million years), Pliocene (8-3 million years);

– Quaternary (3 million - our time): Pleistocene (3 million - 20 thousand years), Holocene (20 thousand years - our time).

The geological era in which we live is called the Cenozoic. This is the era of flowering plants, insects, birds and mammals. The Cenozoic is divided into two unequal periods: Tertiary (67-3 million years) and Quaternary (3 million years - our time). In the first half of the Tertiary period, tropical and subtropical forests were widespread. By the middle of this period, the common ancestral forms of apes and humans became widespread. By the end of the Tertiary period, representatives of all modern families of animals and plants and the vast majority of genera are found.

At this time, the great process of steppeification of the land began, which led to the extinction of some tree and forest forms and to the emergence of others into open space. During the Quaternary period, mammoths, saber-toothed tigers, giant sloths, big-horned turf deer and other animals became extinct. Ancient hunters played a major role in the extinction of large mammals.

Geochronological table- this is one way of representing the stages of development of planet Earth, in particular life on it. The table records eras, which are divided into periods, their age and duration are indicated, and the main aromorphoses of flora and fauna are described.

Often in geochronological tables, earlier, i.e., older, eras are recorded at the bottom, and later, i.e., younger, eras are recorded at the top. Below is data on the development of life on Earth in natural chronological order: from old to new. The tabular form has been omitted for convenience.

Archean era

It began approximately 3500 million (3.5 billion) years ago. Lasted about 1000 million years (1 billion).

In the Archean era, the first signs of life on Earth appeared - single-celled organisms.

According to modern estimates, the age of the Earth is more than 4 billion years. Before the Archean there was the Catarchean era, when there was no life yet.

Proterozoic era

It began approximately 2700 million (2.7 billion) years ago. Lasted for more than 2 billion years.

Proterozoic - the era of early life. Rare and scarce organic remains are found in the layers belonging to this era. However, they belong to all types of invertebrate animals. Also, the first chordates most likely appear - skullless.

Palaeozoic

It began about 570 million years ago and lasted more than 300 million years.

Paleozoic - ancient life. Starting with it, the process of evolution is better studied, since the remains of organisms from higher geological layers are more accessible. Hence, it is customary to examine each era in detail, noting changes in the organic world for each period (although both the Archean and the Proterozoic have their own periods).

Cambrian period (Cambrian)

Lasted about 70 million years. Marine invertebrates and algae thrive. Many new groups of organisms appear - the so-called Cambrian explosion occurs.

Ordovician period (Ordovician)

Lasted 60 million years. The heyday of trilobites and crustaceans. The first vascular plants appear.

Silurian (30 Ma)

• Coral blossom.
• The appearance of scutes - jawless vertebrates.
• The appearance of psilophyte plants coming onto land.

Devonian (60 Ma)

• The flourishing of the coryptaceae.
• Appearance of lobe-finned fishes and stegocephali.
• Distribution of higher spores on land.

Carboniferous period

Lasted about 70 million years.

• The rise of amphibians.
• The appearance of the first reptiles.
• The appearance of flying forms of arthropods.
• Decline in trilobite numbers.
• Fern blossoming.
• The appearance of seed ferns.

Perm (55 million)

• Distribution of reptiles, emergence of wild-toothed lizards.
• Extinction of trilobites.
• Disappearance of coal forests.
• Distribution of gymnosperms.

Mesozoic era

The era of middle life. It began 230 million years ago and lasted about 160 million years.

Triassic

Duration - 35 million years. The flourishing of reptiles, the appearance of the first mammals and true bony fish.

Jurassic period

Lasted about 60 million years.

• Dominance of reptiles and gymnosperms.
• The appearance of Archeopteryx.
• There are many cephalopods in the seas.

Cretaceous period (70 million years)

• The appearance of higher mammals and true birds.
• Wide distribution of bony fish.
• Reduction of ferns and gymnosperms.
• The emergence of angiosperms.

Cenozoic era

An era of new life. It began 67 million years ago and lasts the same amount.

Paleogene

Lasted about 40 million years.

• The appearance of tailed lemurs, tarsiers, parapithecus and dryopithecus.
• Rapid flourishing of insects.
• The extinction of large reptiles continues.
• Entire groups of cephalopods are disappearing.
• Dominance of angiosperms.

Neogene (about 23.5 million years)

Dominance of mammals and birds. The first representatives of the genus Homo appeared.

Anthropocene (1.5 Ma)

The emergence of the species Homo Sapiens. The animal and plant world takes on a modern appearance.

Geological chronology, or geochronology, is based on elucidating the geological history of the best-studied regions, such as Central and Eastern Europe. Based on broad generalizations, comparison of the geological history of various regions of the Earth, patterns of evolution of the organic world, at the end of the last century, at the first International Geological Congresses, the International Geochronological Scale was developed and adopted, reflecting the sequence of divisions of time during which certain complexes of sediments were formed, and the evolution of the organic world . Thus, the international geochronological scale is a natural periodization of the history of the Earth.

Among the geochronological divisions there are: eon, era, period, epoch, century, time. Each geochronological division corresponds to a complex of sediments, identified in accordance with changes in the organic world and called stratigraphic: eonothem, group, system, department, stage, zone. Therefore, a group is a stratigraphic unit, and the corresponding time geochronological unit is an era. Therefore, there are two scales: geochronological and stratigraphic. The first is used when talking about relative time in the history of the Earth, and the second when dealing with sediments, since some geological events occurred in every place on the globe at any time. Another thing is that the accumulation of precipitation was not widespread.

• The Archean and Proterozoic eonothems, covering almost 80% of the Earth's existence, are classified as cryptozoic, since Precambrian formations completely lack skeletal fauna and the paleontological method is not applicable to their dissection. Therefore, the division of Precambrian formations is based primarily on general geological and radiometric data.
• The Phanerozoic eon covers only 570 million years and the division of the corresponding eonothem of sediments is based on a wide variety of numerous skeletal fauna. The Phanerozoic eonothem is divided into three groups: Paleozoic, Mesozoic and Cenozoic, corresponding to major stages of the natural geological history of the Earth, the boundaries of which are marked by rather sharp changes in the organic world.

The names of eonotemes and groups come from Greek words:

• "archeos" - the most ancient, the most ancient;
• "proteros" - primary;
• "paleos" - ancient;
• "mesos" - average;
• "kainos" - new.

The word "cryptos" means hidden, and "phanerozoic" means obvious, transparent, since the skeletal fauna appeared.
The word "zoy" comes from "zoikos" - life. Therefore, the “Cenozoic era” means the era of new life, etc.

Groups are divided into systems, the deposits of which were formed during one period and are characterized only by their own families or genera of organisms, and if these are plants, then by genera and species. Systems have been identified in different regions and at different times since 1822. Currently, 12 systems are recognized, most of whose names come from the places where they were first described. For example, the Jurassic system - from the Jurassic Mountains in Switzerland, the Permian - from the Perm province in Russia, the Cretaceous - from the most characteristic rocks - white writing chalk, etc. The Quaternary system is often called the anthropogenic system, since it is in this age interval that humans appear.

Systems are divided into two or three divisions, which correspond to the early, middle, and late eras. The departments, in turn, are divided into tiers, which are characterized by the presence of certain genera and types of fossil fauna. And finally, the stages are divided into zones, which are the most fractional part of the international stratigraphic scale, to which time corresponds on the geochronological scale. The names of the tiers are usually given by the geographical names of the areas where this tier was identified; for example, Aldanian, Bashkir, Maastrichtian stages, etc. At the same time, the zone is designated by the most characteristic type of fossil fauna. The zone, as a rule, covers only a certain part of the region and is developed over a smaller area than the deposits of the stage.

All divisions of the stratigraphic scale correspond to the geological sections in which these divisions were first identified. Therefore, such sections are standard, typical and are called stratotypes, which contain only their own complex of organic remains, which determines the stratigraphic volume of a given stratotype. Determining the relative age of any layers consists of comparing the discovered complex of organic remains in the studied layers with the complex of fossils in the stratotype of the corresponding division of the international geochronological scale, i.e. the age of sediments is determined relative to the stratotype. That is why the paleontological method, despite its inherent shortcomings, remains the most important method for determining the geological age of rocks. Determining the relative age of, for example, Devonian deposits only indicates that these deposits are younger than the Silurian, but older than the Carboniferous. However, it is impossible to establish the duration of the formation of Devonian deposits and give a conclusion about when (in absolute chronology) the accumulation of these deposits occurred. Only methods of absolute geochronology can answer this question.

Tab. 1. Geochronological table

The problem of determining the absolute age of rocks and the duration of the Earth's existence has long occupied the minds of geologists, and attempts to solve it have been made many times, using various phenomena and processes. Early ideas about the absolute age of the Earth were curious. A contemporary of M.V. Lomonosov, the French naturalist Buffon, determined the age of our planet at only 74,800 years. Other scientists gave different figures, not exceeding 400-500 million years. It should be noted here that all these attempts were doomed to failure in advance, since they were based on the constancy of the rates of processes that, as is known, changed in the geological history of the Earth. And only in the first half of the 20th century. there was a real opportunity to measure the truly absolute age of rocks, geological processes and the Earth as a planet.

The oldest sandstones on Earth are those from Western Australia, the age of zircons in which reaches 4.2 billion years. There are publications about an older absolute age of 5.6 billion years or more, but such figures are not accepted by official science. The age of quartzites from Greenland and Northern Canada is determined at 4 billion years, granites of Australia and South Africa up to 3.8 billion years.

The beginning of the Paleozoic is determined at 570 million years, the Mesozoic - at 240 million years, the Cenozoic - at 67 million years

Archean era. The most ancient rocks exposed on the surface of continents were formed in the Archean era. Recognition of these rocks is difficult, since their outcrops are dispersed and in most cases are covered by thick strata of younger rocks. Where these rocks are exposed, they are so metamorphosed that their original character often cannot be restored. During numerous long stages of denudation, thick strata of these rocks were destroyed, and those that survived contain very few fossil organisms and therefore their correlation is difficult or even impossible. It is interesting to note that the oldest known Archean rocks are probably highly metamorphosed sedimentary rocks, and the older rocks overlain by them were melted and destroyed by numerous igneous intrusions. Therefore, traces of the primary earth's crust have not yet been discovered.

There are two large areas of outcrops of Archean rocks in North America. The first of these, the Canadian Shield, is located in central Canada on both sides of Hudson Bay. Although in some places the Archean rocks are overlain by younger ones, in most of the territory of the Canadian Shield they make up the surface. The oldest rocks known in this area are marbles, slate and crystalline schists, interbedded with lavas. Initially, limestone and shales were deposited here, subsequently sealed by lavas. Then these rocks were exposed to powerful tectonic movements, which were accompanied by large granite intrusions. Ultimately, the sedimentary rocks underwent severe metamorphism. After a long period of denudation, these highly metamorphosed rocks were brought to the surface in places, but the general background is granites.

Outcrops of Archean rocks are also found in the Rocky Mountains, where they form the crests of many ridges and individual peaks, such as Pikes Peak. Younger rocks there have been destroyed by denudation.

In Europe, Archean rocks are exposed in the Baltic Shield within Norway, Sweden, Finland and Russia. They are represented by granites and highly metamorphosed sedimentary rocks. Similar outcrops of Archean rocks are found in the south and southeast of Siberia, China, western Australia, Africa and northeast South America. The oldest traces of the vital activity of bacteria and colonies of unicellular blue-green algae Collenia were discovered in Archean rocks of southern Africa (Zimbabwe) and Ontario (Canada).

Proterozoic era. At the beginning of the Proterozoic, after a long period of denudation, the land was largely destroyed, certain parts of the continents were submerged and were flooded by shallow seas, and some low-lying basins began to be filled with continental sediments. In North America, the most significant exposures of Proterozoic rocks are found in four areas. The first of them is confined to the southern part of the Canadian Shield, where thick layers of shales and sandstones of the considered age are exposed around Lake. Upper and northeast of the lake. Huron. These rocks are of both marine and continental origin. Their distribution indicates that the position of shallow seas changed significantly throughout the Proterozoic. In many places, marine and continental sediments are interbedded with thick lava strata. At the end of sedimentation, tectonic movements of the earth's crust occurred, Proterozoic rocks underwent folding and large mountain systems were formed. In the foothills east of the Appalachians there are numerous outcrops of Proterozoic rocks. They were originally deposited as layers of limestone and shale, and then during orogenesis (mountain building) they metamorphosed into marble, slate and crystalline schist. In the Grand Canyon region, a thick sequence of Proterozoic sandstones, shales and limestones unconformably overlie Archean rocks. In the northern Rocky Mountains, a sequence of Proterozoic limestones with a thickness of ca. 4600 m. Although the Proterozoic formations in these areas were affected by tectonic movements and were folded and broken by faults, these movements were not intense enough and could not lead to metamorphism of the rocks. Therefore, the original sedimentary textures were preserved there.

In Europe, there are significant outcrops of Proterozoic rocks within the Baltic Shield. They are represented by highly metamorphosed marbles and slates. In northwestern Scotland, a thick sequence of Proterozoic sandstones overlies Archean granites and crystalline schists. Extensive outcrops of Proterozoic rocks occur in western China, central Australia, southern Africa and central South America. In Australia, these rocks are represented by a thick sequence of unmetamorphosed sandstones and shales, and in eastern Brazil and southern Venezuela - highly metamorphosed slate and crystalline shales.

Fossil blue-green algae Collenia very widespread on all continents in unmetamorphosed limestones of Proterozoic age, where a few fragments of shells of primitive mollusks were also found. However, the remains of animals are very rare, and this indicates that most organisms had a primitive structure and did not yet have hard shells, which are preserved in the fossil state. Although traces of ice ages are recorded for the early stages of Earth's history, extensive glaciation, which had an almost global distribution, is noted only at the very end of the Proterozoic.

Palaeozoic. After the land experienced a long period of denudation at the end of the Proterozoic, some of its territories experienced subsidence and were flooded by shallow seas. As a result of denudation of elevated areas, sedimentary material was carried by water flows into geosynclines, where strata of Paleozoic sedimentary rocks more than 12 km thick accumulated. In North America, at the beginning of the Paleozoic era, two large geosynclines formed. One of them, called the Appalachian, stretches from the North Atlantic Ocean through southeastern Canada and further south to the Gulf of Mexico along the axis of the modern Appalachians. Another geosyncline connected the Arctic Ocean to the Pacific Ocean, passing slightly east of Alaska to the south through eastern British Columbia and western Alberta, then through eastern Nevada, western Utah and southern California. Thus North America was divided into three parts. In certain periods of the Paleozoic, its central regions were partially flooded and both geosynclines were connected by shallow seas. In other periods, as a result of isostatic uplifts of land or fluctuations in the level of the World Ocean, marine regressions occurred, and then terrigenous material washed away from adjacent elevated areas was deposited in geosynclines.

In the Paleozoic, similar conditions existed on other continents. In Europe, huge seas periodically flooded the British Isles, the territories of Norway, Germany, France, Belgium and Spain, as well as a vast area of ​​the East European Plain from the Baltic Sea to the Ural Mountains. Large outcrops of Paleozoic rocks are also found in Siberia, China and northern India. They are indigenous to most areas of eastern Australia, northern Africa, and northern and central South America.

The Paleozoic era is divided into six periods of unequal duration, alternating with short-term stages of isostatic uplifts or marine regressions, during which sedimentation did not occur within the continents (Fig. 9, 10).

Cambrian period - the earliest period of the Paleozoic era, named after the Latin name for Wales (Cumbria), where rocks of this age were first studied. In North America, in the Cambrian, both geosynclines were flooded, and in the second half of the Cambrian, the central part of the continent occupied such a low position that both troughs were connected by a shallow sea and layers of sandstones, shales and limestones accumulated there. A major marine transgression was taking place in Europe and Asia. These parts of the world were largely flooded. The exceptions were three large isolated landmasses (the Baltic Shield, the Arabian Peninsula and southern India) and a number of small isolated landmasses in southern Europe and southern Asia. Smaller marine transgressions occurred in Australia and central South America. The Cambrian was characterized by rather calm tectonic conditions.

The deposits of this period preserved the first numerous fossils indicating the development of life on Earth. Although no terrestrial plants or animals were recorded, the shallow epicontinental seas and submerged geosynclines were rich in numerous invertebrate animals and aquatic plants. The most unusual and interesting animals of that time were trilobites (Fig. 11), a class of extinct primitive arthropods, which were widespread in the Cambrian seas. Their calcareous-chitinous shells have been found in rocks of this age on all continents. In addition, there were many types of brachiopods, molluscs, and other invertebrates. Thus, all major forms of invertebrate organisms (with the exception of corals, bryozoans and pelecypods) were present in the Cambrian seas.

At the end of the Cambrian period, most of the land experienced uplift and short-term marine regression occurred.

Ordovician period - the second period of the Paleozoic era (named after the Celtic Ordovician tribe that inhabited the territory of Wales). During this period, the continents again experienced subsidence, as a result of which geosynclines and low-lying basins turned into shallow seas. At the end of the Ordovician ca. 70% of North America was flooded by the sea, in which thick layers of limestone and shales were deposited. The sea also covered large areas of Europe and Asia, partly Australia and the central regions of South America.

All Cambrian invertebrates continued to evolve into the Ordovician. In addition, corals, pelecypods (bivalves), bryozoans and the first vertebrates appeared. In Colorado, in Ordovician sandstones, fragments of the most primitive vertebrates were discovered - jawless (ostracoderms), which lacked real jaws and paired limbs, and the front part of the body was covered with bony plates that formed a protective shell.

Based on paleomagnetic studies of rocks, it has been established that throughout most of the Paleozoic, North America was located in the equatorial zone. Fossil organisms and widespread limestones from this time indicate the dominance of warm, shallow seas in the Ordovician. Australia was located near the South Pole, and northwestern Africa was located in the region of the pole itself, which is confirmed by signs of widespread glaciation imprinted in the Ordovician rocks of Africa.

At the end of the Ordovician period, as a result of tectonic movements, continental uplift and marine regression occurred. In some places, the native Cambrian and Ordovician rocks experienced a process of folding, which was accompanied by the growth of mountains. This ancient stage of orogenesis is called the Caledonian folding.

Silurian. For the first time, rocks of this period were also studied in Wales (the name of the period comes from the Celtic tribe of Silures who inhabited this region).

After the tectonic uplifts that marked the end of the Ordovician period, a denudation stage began, and then at the beginning of the Silurian the continents again experienced subsidence, and the seas flooded the low-lying areas. In North America, in the Early Silurian the area of ​​seas decreased significantly, but in the Middle Silurian they occupied almost 60% of its territory. A thick sequence of marine limestones of the Niagara formation was formed, which received its name from the Niagara Falls, the threshold of which it forms. In the Late Silurian, the areas of the seas were greatly reduced. Thick salt-bearing strata accumulated in a strip stretching from modern Michigan to central New York.

In Europe and Asia, the Silurian seas were widespread and occupied almost the same territories as the Cambrian seas. The same isolated massifs as in the Cambrian, as well as significant areas of northern China and Eastern Siberia, remained unflooded. In Europe, thick limestone strata accumulated along the periphery of the southern tip of the Baltic Shield (currently they are partially submerged by the Baltic Sea). Small seas were common in eastern Australia, northern Africa and central South America.

In the Silurian rocks, in general, the same basic representatives of the organic world were found as in the Ordovician. Land plants had not yet appeared in the Silurian. Among invertebrates, corals have become much more abundant, as a result of whose vital activity massive coral reefs have formed in many areas. Trilobites, so characteristic of Cambrian and Ordovician rocks, are losing their dominant significance: they are becoming smaller both in quantity and in species. At the end of the Silurian, many large aquatic arthropods called eurypterids, or crustaceans, appeared.

The Silurian period in North America ended without major tectonic movements. However, in Western Europe at this time the Caledonian belt formed. This mountain range extended across Norway, Scotland and Ireland. Orogenesis also occurred in northern Siberia, as a result of which its territory was raised so high that it was never flooded again.

Devonian named after the county of Devon in England, where rocks of this age were first studied. After the denudation break, certain areas of the continents again experienced subsidence and were flooded by shallow seas. In northern England and partly in Scotland, young Caledonides prevented the penetration of the sea. However, their destruction led to the accumulation of thick strata of terrigenous sandstones in the valleys of foothill rivers. This formation of ancient red sandstones is known for its well-preserved fossil fish. Southern England at this time was covered by a sea in which thick layers of limestone were deposited. Large areas in northern Europe were then flooded by seas in which layers of clayey shales and limestones accumulated. When the Rhine cut into these strata in the area of ​​the Eifel massif, picturesque cliffs were formed that rise along the banks of the valley.

The Devonian seas covered many areas of European Russia, southern Siberia and southern China. A vast sea basin flooded central and western Australia. This area has not been covered by the sea since the Cambrian period. In South America, marine transgression extended to some central and western areas. In addition, there was a narrow sublatitudinal trough in the Amazon. Devonian breeds are very widespread in North America. During most of this period, two major geosynclinal basins existed. In the Middle Devonian, marine transgression spread to the territory of the modern river valley. Mississippi, where a multi-layered strata of limestone has accumulated.

In the Upper Devonian, thick horizons of shale and sandstone formed in the eastern regions of North America. These clastic sequences correspond to a stage of mountain building that began at the end of the Middle Devonian and continued until the end of this period. The mountains extended along the eastern flank of the Appalachian geosyncline (from the modern southeastern United States to southeastern Canada). This region was greatly uplifted, its northern part underwent folding, and then extensive granite intrusions occurred there. These granites are used to make up the White Mountains in New Hampshire, Stone Mountain in Georgia, and a number of other mountain structures. Upper Devonian, so-called The Acadian mountains were reworked by denudation processes. As a result, a layered sequence of sandstones has accumulated to the west of the Appalachian geosyncline, the thickness of which in some places exceeds 1500 m. They are widely represented in the region of the Catskill Mountains, hence the name Catskill sandstones. At the same time, mountain building appeared on a smaller scale in some areas of Western Europe. Orogenesis and tectonic uplift of the earth's surface caused marine regression at the end of the Devonian period.

During the Devonian, some important events occurred in the evolution of life on Earth. The first undisputed discoveries of land plants were made in many areas of the globe. For example, in the vicinity of Gilboa (New York), many species of ferns, including giant trees, were found.

Among the invertebrates, sponges, corals, bryozoans, brachiopods and mollusks were widespread (Fig. 12). There were several types of trilobites, although their numbers and species diversity were significantly reduced compared to the Silurian. The Devonian is often called the “age of fish” due to the magnificent flowering of this class of vertebrates. Although primitive jawless animals still existed, more advanced forms began to predominate. Shark-like fish reached a length of 6 m. At this time, lungfishes appeared, in which the swim bladder was transformed into primitive lungs, which allowed them to exist for some time on land, as well as lobe-finned and ray-finned fish. In the Upper Devonian, the first traces of land animals were discovered - large salamander-like amphibians called stegocephalians. Their skeletal features show that they evolved from lungfishes by further improving their lungs and modifying their fins into limbs.

Carboniferous period. After some break, the continents again experienced subsidence and their low-lying areas turned into shallow seas. Thus began the Carboniferous period, which got its name from the widespread occurrence of coal deposits in both Europe and North America. In America, its early stage, characterized by marine conditions, was previously called Mississippian due to the thick layer of limestone that formed within the modern valley of the river. Mississippian, and is now attributed to the lower Carboniferous period.

In Europe, throughout the Carboniferous period, the territories of England, Belgium and northern France were mostly flooded by the sea, in which thick limestone horizons were formed. Some areas of southern Europe and southern Asia were also flooded, where thick layers of shales and sandstones were deposited. Some of these horizons are continental in origin and contain many fossil remains of terrestrial plants and also host coal-bearing strata. Since Lower Carboniferous formations are poorly represented in Africa, Australia and South America, it can be assumed that these territories were located predominantly in subaerial conditions. In addition, there is evidence of widespread continental glaciation there.

In North America, the Appalachian geosyncline was limited from the north by the Acadian Mountains, and from the south, from the Gulf of Mexico, it was penetrated by the Mississippi Sea, which also flooded the Mississippi Valley. Small sea basins occupied some areas in the west of the continent. In the Mississippi Valley region, a multilayered sequence of limestone and shale accumulated. One of these horizons, the so-called Indian limestone, or spergenite, is a good building material. It was used in the construction of many government buildings in Washington.

At the end of the Carboniferous period, mountain building became widespread in Europe. Chains of mountains stretched from southern Ireland through southern England and northern France into southern Germany. This stage of orogenesis is called Hercynian or Variscian. In North America, local uplifts occurred at the end of the Mississippian period. These tectonic movements were accompanied by marine regression, the development of which was also facilitated by glaciations of the southern continents.

In general, the organic world of the Lower Carboniferous (or Mississippian) time was the same as in the Devonian. However, in addition to a greater variety of types of tree ferns, the flora was replenished with tree mosses and calamites (tree-like arthropods of the horsetail class). Invertebrates were mainly represented by the same forms as in the Devonian. During Mississippian times, sea lilies, bottom-dwelling animals similar in shape to a flower, became more common. Among the fossil vertebrates, shark-like fish and stegocephalians are numerous.

At the beginning of the Late Carboniferous (Pennsylvanian in North America), conditions on the continents began to change rapidly. As follows from the significantly wider distribution of continental sediments, the seas occupied smaller spaces. Northwestern Europe spent most of this time in subaerial conditions. The vast epicontinental Ural Sea extended widely across northern and central Russia, and a major geosyncline extended across southern Europe and southern Asia (the modern Alps, Caucasus, and Himalayas lie along its axis). This trough, called the Tethys geosyncline, or sea, existed over a number of subsequent geological periods.

Lowlands stretched across England, Belgium and Germany. Here, as a result of small oscillatory movements of the earth's crust, an alternation of marine and continental environments occurred. As the sea receded, low-lying swampy landscapes with forests of tree ferns, tree mosses and calamites formed. As the seas advanced, sediments covered the forests, compacting woody remains, which turned into peat and then coal. In Late Carboniferous times, cover glaciation spread across the continents of the Southern Hemisphere. In South America, as a result of marine transgression penetrating from the west, most of the territory of modern Bolivia and Peru was flooded.

In early Pennsylvanian time in North America, the Appalachian geosyncline closed, lost contact with the World Ocean, and terrigenous sandstones accumulated in the eastern and central regions of the United States. During the middle and end of this period, the interior of North America (as well as Western Europe) was dominated by lowlands. Here, shallow seas periodically gave way to swamps that accumulated thick peat deposits that later transformed into large coal basins that stretch from Pennsylvania to eastern Kansas. Parts of western North America were flooded by sea during much of this period. Layers of limestone, shale and sandstone were deposited there.

The widespread occurrence of subaerial environments greatly contributed to the evolution of terrestrial plants and animals. Gigantic forests of tree ferns and club mosses covered the vast swampy lowlands. These forests abounded in insects and arachnids. One species of insect, the largest in geological history, was similar to the modern dragonfly, but had a wingspan of approx. 75 cm. Stegocephalians reached significantly greater species diversity. Some exceeded 3 m in length. In North America alone, more than 90 species of these giant amphibians, which were similar to salamanders, were discovered in swamp sediments of the Pennsylvanian period. The remains of ancient reptiles were found in these same rocks. However, due to the fragmentary nature of the finds, it is difficult to get a complete picture of the morphology of these animals. These primitive forms were probably similar to alligators.

Permian period. Changes in natural conditions, which began in the Late Carboniferous, became even more pronounced in the Permian period, which ended the Paleozoic era. Its name comes from the Perm region in Russia. At the beginning of this period, the sea occupied the Ural geosyncline - a trough that followed the strike of the modern Ural Mountains. A shallow sea periodically covered parts of England, northern France and southern Germany, where layered strata of marine and continental sediments - sandstones, limestones, shales and rock salt - accumulated. The Tethys Sea existed for most of the period, and a thick sequence of limestones formed in the area of ​​northern India and the modern Himalayas. Thick Permian deposits are present in eastern and central Australia and on the islands of South and Southeast Asia. They are widespread in Brazil, Bolivia and Argentina, as well as in southern Africa.

Many Permian formations in northern India, Australia, Africa and South America are of continental origin. They are represented by compacted glacial deposits, as well as widespread fluvio-glacial sands. In Central and Southern Africa, these rocks begin a thick sequence of continental sediments known as the Karoo Series.

In North America, the Permian seas occupied a smaller area compared to previous Paleozoic periods. The main transgression spread from the western Gulf of Mexico north through Mexico and into the south-central United States. The center of this epicontinental sea was located within the modern state of New Mexico, where a thick sequence of Capitanian limestones formed. Thanks to the activity of groundwater, these limestones acquired a honeycomb structure, especially pronounced in the famous Carlsbad Caverns (New Mexico, USA). Farther east, coastal red shale facies were deposited in Kansas and Oklahoma. At the end of the Permian, when the area occupied by the sea was significantly reduced, thick salt-bearing and gypsum-bearing strata formed.

At the end of the Paleozoic era, partly in the Carboniferous and partly in the Permian, orogenesis began in many areas. Thick layers of sedimentary rocks of the Appalachian geosyncline were folded and broken by faults. As a result, the Appalachian Mountains were formed. This stage of mountain building in Europe and Asia is called Hercynian or Variscian, and in North America - Appalachian.

The flora of the Permian period was the same as in the second half of the Carboniferous. However, the plants were smaller and not as numerous. This indicates that the Permian climate became colder and drier. The invertebrate animals of the Permian were inherited from the previous period. A great leap occurred in the evolution of vertebrates (Fig. 13). On all continents, continental sediments of Permian age contain numerous remains of reptiles, reaching a length of 3 m. All of these ancestors of Mesozoic dinosaurs were distinguished by a primitive structure and looked like lizards or alligators, but sometimes had unusual features, for example, a high sail-shaped fin extending from the neck to the tail along the back, in Dimetrodon. Stegocephalians were still numerous.

At the end of the Permian period, mountain building, which manifested itself in many areas of the globe against the background of the general uplift of continents, led to such significant changes in the environment that many characteristic representatives of the Paleozoic fauna began to die out. The Permian period was the final stage of the existence of many invertebrates, especially trilobites.

Mesozoic era, divided into three periods, it differed from the Paleozoic in the predominance of continental settings over marine ones, as well as the composition of flora and fauna. Land plants, many groups of invertebrates, and especially vertebrates have adapted to new environments and undergone significant changes.

Triassic opens the Mesozoic era. Its name comes from the Greek. trias (trinity) in connection with the clear three-membered structure of the sediment strata of this period in northern Germany. Red sandstones lie at the base of the sequence, limestones in the middle, and red sandstones and shales at the top. During the Triassic, large areas of Europe and Asia were occupied by lakes and shallow seas. The epicontinental sea covered Western Europe, and its coastline can be traced to England. The above-mentioned stratotype sediments accumulated in this sea basin. The sandstones occurring in the lower and upper parts of the sequence are partly of continental origin. Another Triassic sea basin penetrated into the territory of northern Russia and spread south along the Ural trough. The huge Tethys Sea then covered approximately the same territory as in the Late Carboniferous and Permian times. In this sea, a thick layer of dolomitic limestone has accumulated, which composes the Dolomites of northern Italy. In south-central Africa, most of the upper strata of the Karoo continental series are Triassic in age. These horizons are known for the abundance of fossil remains of reptiles. At the end of the Triassic, covers of silts and sands of continental origin formed on the territory of Colombia, Venezuela and Argentina. The reptiles found in these layers show striking similarities to the fauna of the Karoo series of southern Africa.

In North America, Triassic rocks are not as widespread as in Europe and Asia. The products of the destruction of the Appalachians - red continental sands and clays - accumulated in depressions located east of these mountains and experienced subsidence. These deposits, interbedded with lava horizons and sheet intrusions, are faulted and dip to the east. In the Newark Basin in New Jersey and the Connecticut River Valley, they correspond to bedrock of the Newark series. Shallow seas occupied some western areas of North America, where limestones and shales accumulated. Continental sandstones and Triassic shales emerge along the sides of the Grand Canyon (Arizona).

The organic world in the Triassic period was significantly different than in the Permian period. This time is characterized by an abundance of large coniferous trees, the remains of which are often found in Triassic continental deposits. The shales of the Chinle Formation in northern Arizona are loaded with fossilized tree trunks. Weathering of the shale has exposed them and now forms a stone forest. Cycads (or cycadophytes), plants with thin or barrel-shaped trunks and dissected leaves hanging from the top, like those of palm trees, have become widespread. Some cycad species also exist in modern tropical areas. Of the invertebrates, the most common were mollusks, among which ammonites predominated (Fig. 14), which had a vague resemblance to modern nautiluses (or boats) and a multi-chambered shell. There were many species of bivalves. Significant progress has occurred in the evolution of vertebrates. Although stegocephalians were still quite common, reptiles began to predominate, among which many unusual groups appeared (for example, phytosaurs, whose body shape was like that of modern crocodiles, and whose jaws were narrow and long with sharp conical teeth). In the Triassic, true dinosaurs first appeared, evolutionarily more advanced than their primitive ancestors. Their limbs were directed downward, rather than outward (like crocodiles), which allowed them to move like mammals and support their bodies above the ground. Dinosaurs walked on their hind legs, maintaining balance with the help of a long tail (like a kangaroo), and were distinguished by their small stature - from 30 cm to 2.5 m. Some reptiles adapted to life in the marine environment, for example, ichthyosaurs, whose body resembled a shark, and the limbs were transformed into something between flippers and fins, and plesiosaurs, whose torso became flattened, the neck elongated, and the limbs turned into flippers. Both of these groups of animals became more numerous in later stages of the Mesozoic era.

Jurassic period got its name from the Jura Mountains (in northwestern Switzerland), composed of multi-layered strata of limestone, shales and sandstones. One of the largest marine transgressions in Western Europe occurred in the Jurassic. A huge epicontinental sea extended over most of England, France, Germany and penetrated into some western regions of European Russia. In Germany there are numerous outcrops of Upper Jurassic lagoonal fine-grained limestones in which unusual fossils have been discovered. In Bavaria, in the famous town of Solenhofen, remains of winged reptiles and both of the known species of the first birds were found.

The Tethys Sea extended from the Atlantic through the southern part of the Iberian Peninsula along the Mediterranean Sea and through South and Southeast Asia to the Pacific Ocean. Most of northern Asia during this period was located above sea level, although epicontinental seas penetrated into Siberia from the north. Continental sediments of Jurassic age are known in southern Siberia and northern China.

Small epicontinental seas occupied limited areas along the coast of western Australia. In the interior of Australia there are outcrops of Jurassic continental sediments. Most of Africa during the Jurassic period was located above sea level. The exception was its northern outskirts, which were flooded by the Tethys Sea. In South America, an elongated narrow sea filled a geosyncline located approximately on the site of the modern Andes.

In North America, the Jurassic seas occupied very limited areas in the west of the continent. Thick strata of continental sandstones and capping shales accumulated in the Colorado Plateau region, especially north and east of the Grand Canyon. Sandstones were formed from sands that made up the desert dune landscapes of the basins. As a result of weathering processes, sandstones have acquired unusual shapes (such as the picturesque pointed peaks in Zion National Park or Rainbow Bridge National Monument, which is an arch rising 94 m above the canyon floor with a span of 85 m; these attractions are located in Utah). The Morrison Shale deposits are famous for the discovery of 69 species of dinosaur fossils. Fine sediments in this area probably accumulated in swampy lowland conditions.

The flora of the Jurassic period was in general terms similar to that existing in the Triassic. The flora was dominated by cycad and coniferous tree species. For the first time, ginkgos appeared - gymnosperms, broad-leaved woody plants with leaves that fall in autumn (probably a link between gymnosperms and angiosperms). The only species of this family, Ginkgo biloba, has survived to this day and is considered the most ancient representative of the trees, truly a living fossil.

The Jurassic invertebrate fauna is very similar to the Triassic. However, reef-building corals became more numerous, and sea urchins and mollusks became widespread. Many bivalves related to modern oysters appeared. Ammonites were still numerous.

Vertebrates were represented mainly by reptiles, since stegocephalians became extinct at the end of the Triassic. Dinosaurs have reached the culmination of their development. Herbivorous forms such as Apatosaurus and Diplodocus began to move on four limbs; many had long necks and tails. These animals acquired gigantic sizes (up to 27 m in length), and some weighed up to 40 tons. Some representatives of smaller herbivorous dinosaurs, such as stegosaurs, developed a protective shell consisting of plates and spines. Carnivorous dinosaurs, in particular allosaurs, developed large heads with powerful jaws and sharp teeth; they reached a length of 11 m and moved on two limbs. Other groups of reptiles were also very numerous. Plesiosaurs and ichthyosaurs lived in the Jurassic seas. For the first time, flying reptiles appeared - pterosaurs, which developed membranous wings, like bats, and their mass decreased due to tubular bones.

The appearance of birds in the Jurassic is an important stage in the development of the animal world. Two bird skeletons and feather imprints were discovered in the lagoonal limestones of Solenhofen. However, these primitive birds still had many features in common with reptiles, including sharp, conical teeth and long tails.

The Jurassic period ended with intense folding, which resulted in the formation of the Sierra Nevada Mountains in the western United States, which extended further north into modern western Canada. Subsequently, the southern part of this folded belt again experienced uplift, which predetermined the structure of modern mountains. On other continents, manifestations of orogenesis in the Jurassic were insignificant.

Cretaceous period. At this time, thick layered strata of soft, weakly compacted white limestone—chalk—accumulated, from which the period took its name. For the first time, such layers were studied in outcrops along the shores of the Pas-de-Calais Strait near Dover (Great Britain) and Calais (France). In other parts of the world, sediments of this age are also called Cretaceous, although other types of rocks are also found there.

During the Cretaceous period, marine transgressions covered large parts of Europe and Asia. In central Europe, the seas filled two sublatitudinal geosynclinal troughs. One of them was located within southeastern England, northern Germany, Poland and western regions of Russia and in the extreme east reached the submeridional Ural trough. Another geosyncline, Tethys, maintained its previous strike in southern Europe and northern Africa and connected with the southern tip of the Ural trough. Further, the Tethys Sea continued in South Asia and east of the Indian Shield it connected with the Indian Ocean. With the exception of the northern and eastern margins, the territory of Asia was not flooded by the sea throughout the entire Cretaceous period, so continental deposits of this time are widespread there. Thick layers of Cretaceous limestone are present in many areas of Western Europe. In the northern regions of Africa, where the Tethys Sea entered, large strata of sandstones accumulated. The sands of the Sahara Desert were formed mainly due to the products of their destruction. Australia was covered by Cretaceous epicontinental seas. In South America, during most of the Cretaceous period, the Andean trough was flooded by the sea. To the east, terrigenous silts and sands with numerous remains of dinosaurs were deposited over a large area of ​​Brazil.

In North America, marginal seas occupied the coastal plains of the Atlantic Ocean and the Gulf of Mexico, where sands, clays and cretaceous limestones accumulated. Another marginal sea was located on the western coast of the mainland within California and reached the southern foot of the revived Sierra Nevada mountains. However, the most recent major marine transgression occurred in western central North America. At this time, a vast geosynclinal trough of the Rocky Mountains formed, and a huge sea spread from the Gulf of Mexico through the modern Great Plains and Rocky Mountains north (west of the Canadian Shield) all the way to the Arctic Ocean. During this transgression, a thick layered sequence of sandstones, limestones and shales was deposited.

At the end of the Cretaceous period, intense orogeny occurred in South and North America and East Asia. In South America, sedimentary rocks accumulated in the Andean geosyncline over several periods were compacted and folded, leading to the formation of the Andes. Similarly, in North America, the Rocky Mountains formed at the site of a geosyncline. Volcanic activity has increased in many areas of the world. Lava flows covered the entire southern part of the Hindustan Peninsula (thus forming the vast Deccan Plateau), and small outpourings of lava took place in Arabia and East Africa. All continents experienced significant uplifts, and regression of all geosynclinal, epicontinental and marginal seas occurred.

The Cretaceous period was marked by several major events in the development of the organic world. The first flowering plants appeared. Their fossil remains are represented by leaves and wood of species, many of which still grow today (for example, willow, oak, maple and elm). The Cretaceous invertebrate fauna is generally similar to the Jurassic. Among vertebrates, the species diversity of reptiles reached a culmination. There were three main groups of dinosaurs. Carnivores with well-developed massive hind limbs were represented by tyrannosaurs, which reached 14 m in length and 5 m in height. A group of bipedal herbivorous dinosaurs (or trachodonts) with wide flattened jaws, reminiscent of a duck's beak, developed. Numerous skeletons of these animals are found in the Cretaceous continental deposits of North America. The third group includes horned dinosaurs with a developed bony shield that protected the head and neck. A typical representative of this group is Triceratops with a short nasal and two long supraorbital horns.

Plesiosaurs and ichthyosaurs lived in the Cretaceous seas, and sea lizards called mosasaurs with an elongated body and relatively small flipper-like limbs appeared. Pterosaurs (flying lizards) lost their teeth and moved better in air space than their Jurassic ancestors. One type of pterosaur, Pteranodon, had a wingspan of up to 8 m.

There are two known species of birds of the Cretaceous period that retained some morphological features of reptiles, for example, conical teeth located in the alveoli. One of them, hesperornis (a diving bird), has adapted to life in the sea.

Although transitional forms more similar to reptiles than to mammals have been known since the Triassic and Jurassic, numerous remains of true mammals were first discovered in continental Upper Cretaceous sediments. The primitive mammals of the Cretaceous period were small in size and somewhat reminiscent of modern shrews.

Widespread mountain building processes on Earth and tectonic uplifts of continents at the end of the Cretaceous period led to such significant changes in nature and climate that many plants and animals became extinct. Among the invertebrates, the ammonites that dominated the Mesozoic seas disappeared, and among the vertebrates, all dinosaurs, ichthyosaurs, plesiosaurs, mosasaurs and pterosaurs disappeared.

Cenozoic era, covering the last 65 million years, is divided into Tertiary (in Russia it is customary to distinguish two periods - Paleogene and Neogene) and Quaternary periods. Although the latter was of short duration (age estimates of its lower limit range from 1 to 2.8 million years), it played a great role in the history of the Earth, since repeated continental glaciations and the appearance of humans are associated with it.

Tertiary period. At this time, many areas of Europe, Asia and North Africa were covered by shallow epicontinental and deep geosynclinal seas. At the beginning of this period (in the Neogene), the sea occupied southeastern England, northwestern France and Belgium, and a thick layer of sands and clays accumulated there. The Tethys Sea still existed, stretching from the Atlantic to the Indian Ocean. Its waters flooded the Iberian and Apennine peninsulas, the northern regions of Africa, southwest Asia and the north of Hindustan. Thick limestone horizons were deposited in this basin. Much of northern Egypt is composed of nummulitic limestones, which were used as building material in the construction of the pyramids.

At this time, almost all of southeast Asia was occupied by marine basins and a small epicontinental sea extended to the southeast of Australia. Tertiary marine basins covered the northern and southern ends of South America, and the epicontinental sea penetrated into eastern Colombia, northern Venezuela, and southern Patagonia. Thick strata of continental sands and silts accumulated in the Amazon basin.

The marginal seas were located on the site of the modern Coastal Plains adjacent to the Atlantic Ocean and the Gulf of Mexico, as well as along the western coast of North America. Thick strata of continental sedimentary rocks, formed as a result of denudation of the revived Rocky Mountains, accumulated on the Great Plains and in the intermountain basins.

In many areas of the globe, active orogenesis occurred in the middle of the Tertiary period. The Alps, Carpathians and Caucasus formed in Europe. In North America, during the final stages of the Tertiary period, the Coast Ranges (within the modern states of California and Oregon) and the Cascade Mountains (within Oregon and Washington) were formed.

The Tertiary period was marked by significant progress in the development of the organic world. Modern plants arose back in the Cretaceous period. Most tertiary invertebrates were directly inherited from Cretaceous forms. Modern bony fish have become more numerous, and the number and species diversity of amphibians and reptiles have decreased. There was a leap in the development of mammals. From primitive forms similar to shrews and first appearing in the Cretaceous period, many forms originate, dating back to the beginning of the Tertiary period. The most ancient fossil remains of horses and elephants were found in the Lower Tertiary rocks. Carnivores and even-toed ungulates appeared.

The species diversity of animals increased greatly, but many of them became extinct by the end of the Tertiary period, while others (like some Mesozoic reptiles) returned to a marine lifestyle, such as cetaceans and porpoises, whose fins are transformed limbs. Bats were able to fly thanks to a membrane connecting their long fingers. Dinosaurs, which went extinct at the end of the Mesozoic, gave way to mammals, which became the dominant class of animals on land at the beginning of the Tertiary period.

Quaternary period divided into Eopleistocene, Pleistocene and Holocene. The latter began just 10,000 years ago. The modern relief and landscapes of the Earth were mainly formed in the Quaternary period.

Mountain building, which occurred at the end of the Tertiary period, predetermined a significant rise of continents and regression of the seas. The Quaternary period was marked by a significant cooling of the climate and the widespread development of glaciation in Antarctica, Greenland, Europe and North America. In Europe, the center of glaciation was the Baltic Shield, from where the ice sheet extended to southern England, central Germany and the central regions of Eastern Europe. In Siberia, cover glaciation was smaller, mainly limited to foothill areas. In North America, ice sheets covered a vast area, including most of Canada and the northern regions of the United States down to southern Illinois. In the Southern Hemisphere, the Quaternary ice sheet is characteristic not only of Antarctica, but also of Patagonia. In addition, mountain glaciation was widespread on all continents.

In the Pleistocene, there are four main stages of intensified glaciation, alternating with interglacial periods, during which natural conditions were close to modern or even warmer. The last ice cover in Europe and North America reached its greatest extent 18-20 thousand years ago and finally melted at the beginning of the Holocene.

During the Quaternary period, many tertiary forms of animals became extinct and new ones appeared, adapted to colder conditions. Of particular note are the mammoth and woolly rhinoceros, which inhabited the northern regions in the Pleistocene. In the more southern regions of the Northern Hemisphere, mastodons, saber-toothed tigers, etc. were found. When the ice sheets melted, representatives of the Pleistocene fauna died out and modern animals took their place. Primitive people, in particular Neanderthals, probably existed already during the last interglacial, but modern humans are homo sapiens (Homo sapiens)- appeared only in the last glacial epoch of the Pleistocene, and in the Holocene it spread throughout the globe.