The Archean era is the second longest (900 million years) after the Proterozoic. Its end is separated from our time by more than 2.5 billion years. In the Archean era, the first living organisms arose. They were heterotrophs and used the organic compounds of the "primary broth" as food. Conditions for ancient earth changed, and the abiogenic occurrence of organic and inorganic molecules on a planetary scale ceased. Separate small loci remained, mainly at the bottom of the ocean, where the formation of the simplest organic compounds still occurs, but their contribution to the provision of heterotrophs with nutrition is practically negligible.

The depletion of organic matter in the oceans has brought the existence of life to the brink of disaster.

The most important stage in the evolution of life on Earth is associated with the emergence of ancient prokaryotes photosynthesis - biogenic synthesis of organic molecules from inorganic ones due to the energy of sunlight, which led to the separation organic world to plant and animal. The first photosynthetic organisms were prokaryotic blue-green - cyanide. They, having ceased to depend on ready-made organic molecules of the "primary soup", began to develop rapidly. It is especially important that they opened another way for life on Earth.

Photosynthesis is accompanied by the release of a by-product - oxygen. For a billion years, it saturated the water where the first living organisms lived, and was released into the atmosphere.

Microscopic cyanide have left many traces of their existence. They, capturing particles of silt, layer by layer created huge structures, the so-called stromatolites, which exist in a noticeably reduced version at the present time, in particular, off the coast of Australia and on the coast of Florida.

Almost everything that has come down to us since those ancient times is exhausted by the remains of stromatolites.

Cyanea and then appeared eukaryotic green algae released free oxygen from the ocean into the atmosphere, which contributed to the emergence of bacteria capable of living in an aerobic environment. Apparently, at the same time - on the border of the Archean and Proterozoic eras - two more major evolutionary events occurred: sexual process and multicellularity.

To better understand the meaning of the last two aromorphoses, let us dwell on them in more detail. Haploid organisms (microorganisms, blue-green) have one set of chromosomes. Each new mutation immediately manifests itself in the phenotype. If the mutation is beneficial, it is preserved by selection; if it is harmful, the organism carrying it is eliminated by selection. Haploid forms continuously adapt to the environment, but they do not develop fundamentally new features and properties.

The sexual process sharply increases the possibility of adapting to environmental conditions due to the creation of countless combinations of genes in chromosomes. diploidy, arising simultaneously with the formed nucleus, allows you to save mutations in a heterozygous state and use them as reserve of hereditary variability for further developments. In addition, in the heterozygous state, many mutations often increase the viability of individuals and, therefore, increase their chances in the struggle for existence.

The emergence of diploidy and genetic diversity of unicellular eukaryotes, on the one hand, led to the heterogeneity of the structure of cells and their association in colonies, on the other hand, the possibility of a “division of labor” between the cells of the colony, i.e. the formation of multicellular organisms. The separation of cell functions in the first colonial multicellular organisms led to the formation of primary tissues - ectoderm and endoderm, differentiated in structure depending on the function performed. Further differentiation of tissues created the diversity needed to expand the structural and functional capabilities of the organism as a whole, resulting in the creation of more and more complex organs. The improvement of the interaction between cells, first contact, and then mediated through the nervous and endocrine systems, ensured the existence of a multicellular organism as a whole with a complex and subtle interaction of its parts and a corresponding response to the environment.

The paths of evolutionary transformations of the first multicellular organisms were different. Some moved to a sedentary lifestyle and turned into organisms of the type sponges. Others began to crawl, move along the substrate with the help of cilia. From them came flatworms. Still others retained a floating lifestyle, acquired a mouth and gave rise to coelenterates.

Anchor points

• Life originated on Earth from abiogenically synthesized organic molecules.
• AT archean era, on the border with the Proterozoic, the emergence of the first cells marked the beginning of biological evolution.

Questions and tasks for repetition

• 1. By what principle is the history of the Earth divided into eras and periods?
• 2. Recall the material of the chapter. Describe when and how the first living organisms arose.
• 3. What life forms was represented by the living world in the Proterozoic era?

Archean era. The most ancient rocks exposed on the surface of the 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 it is often impossible to restore their original character. During numerous long stages of denudation, thick strata of these rocks were destroyed, and the remaining ones 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, while 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.

AT North America there are two large areas of outcrops of Archean rocks. The first of them - the Canadian Shield - is located in central Canada on both sides of the Hudson Bay. Although in places the Archean rocks are overlain by younger ones, they form the day surface in most of the territory of the Canadian Shield. The oldest known rocks in this area are represented by marbles, slates and crystalline schists interbedded with lavas. Initially, limestones and shales were deposited here, later sealed by lavas. Then these rocks experienced the impact of powerful tectonic movements, which were accompanied by large granite intrusions. Ultimately, the sedimentary rock strata underwent strong metamorphism. After a long period of denudation, these highly metamorphosed rocks were brought to the surface in places, but granites form the general background.

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. The younger rocks there are destroyed by denudation.

In Europe, Archean rocks are exposed on the territory of 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 found in the Archean rocks of southern Africa (Zimbabwe) and the province of Ontario (Canada).

Proterozoic era

Proterozoic era. At the beginning of the Proterozoic, after a long period of denudation, the land was largely destroyed, some parts of the continents experienced subsidence and were flooded by shallow seas, and some low-lying basins began to be filled with continental deposits. In North America, the most significant exposures of Proterozoic rocks are found in four regions. The first of them is confined to the southern part of the Canadian Shield, where thick strata of shales and sandstones of the age under consideration are exposed around the lake. Upper and northeast of the lake. Huron. These rocks are of both marine and continental origin. Their distribution indicates that the position of the shallow seas changed significantly during the Proterozoic. In many places, marine and continental sediments are interbedded with thick lava sequences. At the end of sedimentation, tectonic movements of the earth's crust took place, the Proterozoic rocks underwent folding, and large mountain systems were formed. In the foothills east of the Appalachians, there are numerous outcrops of Proterozoic rocks. Initially, they were deposited in the form of layers of limestone and shale, and then during orogeny (mountain building) they metamorphosed and turned into marble, slate and crystalline schists. In the Grand Canyon area, a thick sequence of Proterozoic sandstones, shales, and limestones unconformably overlies Archean rocks. In the northern part of the Rocky Mountains, a sequence of Proterozoic limestones with a thickness of approx. 4600 m. Although the Proterozoic formations in these areas were affected by tectonic movements and were crumpled into folds and broken by faults, these movements were not intense enough and could not lead to rock metamorphism. 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 the northwest of Scotland, a thick stratum of Proterozoic sandstones overlies Archean granites and crystalline schists. Extensive outcrops of Proterozoic rocks are found in western China, central Australia, southern Africa, and central South America. In Australia, these rocks are represented by a thick sequence of non-metamorphosed sandstones and shales, while in eastern Brazil and southern Venezuela, they are strongly metamorphosed slates and crystalline schists.

Fossil blue-green algae Collenia are very widespread on all continents in non-metamorphosed limestones of the 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 were distinguished by a primitive structure and did not yet have hard shells that are preserved in a fossil state. Although traces of ice ages are recorded for the early stages of the history of the Earth, extensive glaciation, which had an almost global distribution, is noted only at the very end of the Proterozoic.

The age of the Earth is about 4.6 billion years. Life on Earth originated in the ocean more than 3.5 billion years ago.

The history of the development of life on Earth is studied by the fossil remains of organisms or traces of their vital activity. They are found in rocks of different ages.

The geochronological scale of the history of the development of the organic world of the Earth includes eras and periods. The following eras are distinguished:

• archean (archean) - the era of ancient life,
• Proterozoic (Proterozoic) - the era of primary life,
• Paleozoic (Paleozoic) - the era of ancient life,
• Mesozoic (Mesozoic) - the era of middle life,
• Cenozoic (Cenozoic) - the era of new life.

The names of the periods are formed either from the names of the localities where the corresponding deposits were first found (the city of Perm, the county of Devon), or from the processes taking place at that time (during the coal period - Carboniferous - deposits of coal were laid, in the Cretaceous - chalk, etc. .).

Archean era (era of ancient life: 3500 (3800-2600) million years ago)

According to various sources, the first living organisms on Earth appeared 3.8-3.2 billion years ago. These were prokaryotic heterotrophic anaerobes(pre-nuclear, feeding on ready-made organic substances, not needing oxygen). They lived in the primary ocean and fed on organic substances dissolved in its water, created abiogenically from inorganic substances under the influence of the energy of the ultraviolet rays of the Sun and lightning discharges.

The Earth's atmosphere consisted mainly of CO 2 , CO, H 2 , N 2 , water vapor, small amounts of NH 3 , H 2 S, CH 4 and almost did not contain free oxygen O 2 . The absence of free oxygen made it possible for abiogenically created organic substances to accumulate in the ocean, otherwise they would immediately be broken down by oxygen.

The first heterotrophs carried out the oxidation of organic substances anaerobically - without the participation of oxygen by fermentation. During fermentation, organic matter is not completely broken down, and little energy is generated. For this reason, evolution in the early stages of the development of life was very slow.

Over time, heterotrophs greatly multiplied and they began to lack abiogenically created organic matter. Then arose prokaryotic autotrophic anaerobes. They could synthesize organic substances from inorganic substances on their own, first through chemosynthesis, and then through photosynthesis.

The first was photosynthesis anaerobic, which was not accompanied by the release of oxygen:

6CO 2 + 12H 2 S → C 6 H 12 O 6 + 12S + 6H 2 O

Then came aerobic photosynthesis:

6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2

Aerobic photosynthesis was characteristic of creatures similar to modern cyanobacteria.

The free oxygen released during photosynthesis began to oxidize divalent iron, sulfur and manganese compounds dissolved in ocean water. These substances turned into insoluble forms and settled on the ocean floor, where they formed deposits of iron, sulfur and manganese ores, which are currently used by man.

Oxidation of substances dissolved in the ocean took place over hundreds of millions of years, and only when their reserves in the ocean were exhausted did oxygen begin to accumulate in the water and diffuse into the atmosphere.

It should be noted that the obligatory condition for the accumulation of oxygen in the ocean and atmosphere was the burial of some part of the organic matter synthesized by organisms at the bottom of the ocean. Otherwise, if all organics were split with the participation of oxygen, there would be no excess of it and oxygen could not accumulate. Undecomposed bodies of organisms settled on the ocean floor, where they formed deposits of fossil fuels - oil and gas.

The accumulation of free oxygen in the ocean made it possible for autotrophic and heterotrophic aerobes. This happened when the concentration of O 2 in the atmosphere reached 1% of the current level (and it is 21%).

During aerobic oxidation (respiration), organic substances are broken down to end products - CO 2 and H 2 O and 18 times more energy is generated than during oxygen-free oxidation (fermentation):

C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + 38ATP

Since much more energy was released during aerobic processes, the evolution of organisms accelerated significantly.

As a result of the symbiosis of various prokaryotic cells, the first eukaryotes(nuclear).

As a result of the evolution of eukaryotes, sexual process- the exchange of organisms with genetic material - DNA. Thanks to the sexual process, evolution went even faster, since combinative variability was added to the mutational variability.

At first, eukaryotes were single-celled, and then the first multicellular organisms. The transition to multicellularity in plants, animals and fungi occurred independently of each other.

Multicellular organisms have received a number of advantages over unicellular ones:

1. a longer duration of ontogeny, since during individual development the body is replacing some cells with others;
2. numerous offspring, since the organism can allocate more cells for reproduction;
3. significant size and diverse body structure, which provides greater resistance to external environmental factors due to the stability of the internal environment of the body.

Scientists do not have a common opinion on the question of when the sexual process and multicellularity arose - in the Archean or Proterozoic era.

Proterozoic era (era of primary life: 2600-570 Ma)

The appearance of multicellular organisms accelerated evolution even more and, in a relatively short period (on a geological time scale), different kinds living organisms adapted to different conditions of existence. New forms of life occupied and formed ever new ecological niches in different areas and depths of the ocean. Rocks 580 million years old already contain the imprints of creatures with hard skeletons, and therefore it is much easier to study evolution from this period. Solid skeletons serve as a support for the bodies of organisms and contribute to an increase in their size.

By the end of the Proterozoic era (570 million years ago), a producer-consumer system was formed and an oxygen-carbon biogeochemical cycle of substances was formed.

Paleozoic era (era of ancient life: 570-240 million years ago)

During the first period of the Paleozoic Era, Cambrian(570-505 million years ago) - there was a so-called "evolutionary explosion": in a short time, almost all currently known types of animals were formed. All the evolutionary time preceding this period was called Precambrian, or cryptozoic("era hidden life”) is 7/8 of the history of the Earth. The time after the Cambrian was called Phanerozoic(“the era of manifest life”).

As more and more oxygen was formed, the atmosphere gradually acquired oxidizing properties. When the concentration of O 2 in the atmosphere reached 10% of the current level (at the border of the Silurian and Devonian), at an altitude of 20-25 km, an ozone layer began to form in the atmosphere. It was formed from O 2 molecules under the influence of the energy of the ultraviolet rays of the Sun:

O 2 → O + O
O 2 + O → O 3

Ozone molecules (O 3) have the ability to reflect ultraviolet rays. As a result, the ozone shield has become a protection for living organisms from harmful ultraviolet rays in large doses. Before that, water served as protection. Now life has the opportunity to move out of the ocean onto land.

The emergence of living beings on land began in the Cambrian period: bacteria were the first to enter it, and then fungi and lower plants. As a result, soil was formed on land and in Silurian(435-400 million years ago), the first vascular plants appeared on land - psilophytes. Exit to land contributed to the appearance in plants of tissues (integumentary, conductive, mechanical, etc.) and organs (root, stem, leaves). As a result, higher plants appeared. The first land animals were arthropods, descended from marine crustaceans.

At this time, chordates evolved in the marine environment: vertebrate fish originated from invertebrate chordates, and amphibians from lobe-finned fish in the Devonian. They dominated the land for 75 million years and were represented by very large forms. In the Permian period, when the climate became colder and drier, reptiles gained superiority over amphibians.

Mesozoic era (era of middle life: 240-66 million years ago)

In the Mesozoic era - the "era of dinosaurs" - reptiles reached their peak (their numerous forms were formed) and decline. In the Triassic, crocodiles and turtles appeared, and the class Mammals originated from the animal-toothed reptiles. Throughout the Mesozoic era, mammals were small and not widely distributed. At the end of the Cretaceous, a cooling set in and a mass extinction of reptiles occurred, the final causes of which have not been fully elucidated. AT Cretaceous angiosperms (flowering) appeared.

Cenozoic era (era of new life: 66 million years ago - present)

In the Cenozoic era, mammals, birds, arthropods, and flowering plants were widely distributed. A man appeared.

At present, human activity has become an important factor development of the biosphere.

Life originated in the Archean era. Since the first living organisms did not yet have any skeletal formations, there were almost no traces of them left. However, the presence among the Archean deposits of rocks of organic origin - limestone, marble, graphite and others - indicates the existence of primitive living organisms in this era. They were unicellular pre-nuclear organisms (prokaryotes): bacteria and blue-green algae.

Life in water was possible due to the fact that water protected organisms from the harmful effects of ultraviolet rays. That is why the sea could become the cradle of life.

4 major events of the Archean era

In the Archean era, four major events (aromorphosis) occurred in the evolution of the organic world and the development of life:

• Eukaryotes appeared;
• photosynthesis;
• sexual process;
• multicellularity.

The emergence of eukaryotes is associated with the formation of cells that have a real nucleus (containing chromosomes) and mitochondria. Only such cells are able to divide mitotically, which ensured good preservation and transfer of genetic material. This was a prerequisite for the emergence of the sexual process.

The first inhabitants of our planet were heterotrophic and fed on organic substances of abiogenic origin, dissolved in the original ocean. The progressive development of primary living organisms subsequently provided a huge leap (aromorphosis) in the development of life: the emergence of autotrophs that use solar energy to synthesize organic compounds from the simplest inorganic ones.

Of course, such a complex compound as chlorophyll did not immediately appear. Initially, more simply arranged pigments appeared, which contributed to the assimilation of organic substances. Chlorophyll apparently developed from these pigments.

Over time, organic matter accumulated in it abiogenically began to dry out in the primordial ocean. The emergence of autotrophic organisms, primarily green plants capable of photosynthesis, provided further continuous synthesis of organic substances, thanks to the use of solar energy (the cosmic role of plants), and consequently, the existence and further development of life.

With the advent of photosynthesis, the organic world diverged into two stems, differing in the way of nutrition. Thanks to the emergence of autotrophic photosynthetic plants, water and the atmosphere began to be enriched with free oxygen. This predetermined the possibility of the emergence of aerobic organisms capable of more efficient use of energy in the process of life.

The accumulation of oxygen in the atmosphere led to the formation of an ozone screen in its upper layers, which does not let in harmful ultraviolet rays. This paved the way for life to land on land. The appearance of photosynthetic plants made possible the existence and progressive development of heterotrophic organisms.

The appearance of the sexual process led to the emergence of combinative variability, supported by selection. Finally, multicellular organisms apparently evolved from colonial flagellates in this era. The appearance of the sexual process and multicellularity prepared further progressive evolution.

Archean era- this is the first stage in the development of life on earth, an exciting time interval of 1.5 billion years. It originates 4 billion years ago. During the Archean era, the flora and fauna of the planet begin to emerge, from here the history of dinosaurs, mammals and humans begins. The first deposits of the natural wealth of nature appear. There were no mountain heights and the oceans, there was not enough oxygen. The atmosphere was mixed with the hydrosphere into a single whole - this prevented the sun's rays from reaching the earth.

The Archean era in translation from ancient Greek means "ancient". This era is divided into 4 periods - Eoarchean, Paleoarchean, Mesoarchean and Neoarchean.

The first period of the Archean era lasted approximately 400 million years. This period is characterized by increased meteor showers, the formation of volcanic craters and the earth's crust. Active formation of the hydrosphere begins, salty reservoirs isolated from each other appear with hot water. The atmosphere is dominated by carbon dioxide, the air temperature reaches 120 °C. The first living organisms appear - cyanobacteria, which begin to produce oxygen through photosynthesis. The formation of Vaalbara, the main earthly continent, takes place.

paleoarchaean

The next period of the Archean era captures a period of time of 200 million years. The Earth's magnetic field is enhanced by increasing the hardness of the Earth's core. This favorably affects the conditions of life and development of the simplest microorganisms. Days last about 15 hours. The oceans are being formed. Changes in submarine ridges lead to a slow increase in the volume of water and a decrease in the amount of carbon dioxide in the atmosphere. The formation of the first terrestrial continent continues. Mountain ranges do not yet exist. Instead, active volcanoes rise above the ground.

Mesoarchean

The third period of the Archean era lasted 400 million years. At this time, the main continent split into 2 parts. As a result of a sharp cooling of the planet, in which constant volcanic processes are to blame, the Pongol glacial formation is formed. During this period, the number of cyanobacteria begins to actively grow. Chemolithotrophic organisms develop that do not need oxygen and sunlight. Vaalbar is fully formed. Its size is approximately equal to the size of modern Madagascar. The formation of the Ur continent begins. Large islands slowly begin to form from volcanoes. The atmosphere is still dominated by carbon dioxide. The air temperature remains high.

The last period of the Archean era ended 2.5 billion years ago. At this stage, the formation of the earth's crust is completed, the level of oxygen in the atmosphere increases. The mainland of Ur becomes the basis of Kenorland. Most of the planet is occupied by volcanoes. Their vigorous activity leads to increased formation of minerals. Gold, silver, granites, diorites and other equally important natural resources were formed during the Neoarchean period. AT last centuries of the Archean era the first multicellular organisms appear, which later divided into terrestrial and marine inhabitants. Bacteria begin the development of the sexual process of reproduction. Haploid microorganisms have one chromosome set. They are constantly adapting to changes in their environment, but they do not have other properties. The sexual process allowed adaptation to life with changes in the set of chromosomes. This made it possible for the further evolution of living organisms.

Flora and fauna of the Archean era

The flora of this era cannot boast of diversity. The only kind Plants are unicellular filamentous algae - spheromorphids - the habitat of bacteria. When these algae form in colonies, they can be seen without special instruments. They can go free swimming or attach themselves to the surface of something. In the future, algae will form new form life - lichens.

During the Archean era, the first prokaryotes- single-celled organisms that do not have a nucleus. With the help of photosynthesis, prokaryotes produce oxygen and create favorable conditions for the emergence of new forms of life. Prokaryotes are divided into two domains - bacteria and archaea.

Archaea

It has now been established that they have features that distinguish them from other living organisms. Therefore, the classification that combines them with bacteria in one group is considered outdated. Outwardly, archaea are similar to bacteria, but some have unusual shapes. These organisms can absorb both sunlight and carbon. They can exist in the most unsuitable conditions for life. One type of archaea is food for marine life. Several species have been found in the human intestine. They take part in the processes of digestion. Other species are used to clean sewage ditches and ditches.

There is an unconfirmed theory that during the Archean era, the emergence and development of eukaryotes, microorganisms of the kingdom of fungi, similar to yeast fungi, occurred.

The fact that life on earth originated during the Archean era is evidenced by the found fossilized stromalites - waste products of cyanobacteria. The first stromatolites were discovered in Canada, Siberia, Australia and Africa. Scientists have proven that it was bacteria that had a huge impact on the formation of aragonite crystals, which is found in mollusk shells and is part of corals. Thanks to cyanobacteria, deposits of carbonate and siliceous formations arose. Colonies of ancient bacteria look like mold. They were located in the area of ​​volcanoes, and at the bottom of lakes, and in coastal areas.

Archean climate

Scientists have not yet been able to learn anything about the climatic zones of this period. The existence of zones of different climates in the Archean era can be judged by ancient glacial deposits - tillites. The remains of glaciations are now found in America, Africa, and Siberia. It is not yet possible to determine their true dimensions. Most likely, glacial deposits covered only the mountain peaks, because the vast continents during the Archean era had not yet been formed. The existence of a warm climate in some areas of the planet is indicated by the development of flora in the oceans.

Hydrosphere and Atmosphere of the Archean Era

AT early period there was little water on the ground. The water temperature during the Archean era reached 90°C. This indicates the saturation of the atmosphere with carbon dioxide. There was very little nitrogen in it, there was almost no oxygen in the early stages, the remaining gases are quickly destroyed under the influence of sunlight. The temperature of the atmosphere reaches 120 degrees. If nitrogen prevailed in the atmosphere, then the temperature would not be lower than 140 degrees.

In the late period, after the formation of the world ocean, the level of carbon dioxide began to decrease markedly. The temperature of water and air also dropped. And the amount of oxygen increased. Thus, the planet gradually became habitable for various organisms.

Minerals of Archaea

It is in the Archean era that the greatest formation of minerals occurs. This is facilitated by the active activity of volcanoes. Colossal deposits of iron, gold, uranium and manganese ores, aluminum, lead and zinc, copper, nickel and cobalt ores were laid by this era of the life of the earth. Within the territory of Russian Federation Archean deposits have been found in the Urals and Siberia.

In details periods of the archean era will be discussed in the next lectures.