Scientists divide the history of the Earth into long periods of time - eras. Eras are divided into periods, periods - into epochs, epochs - into centuries.
The division into eras is not accidental. The end of one era and the beginning of another was marked by a significant transformation of the face of the Earth, a change in the ratio of land and sea, and intensive mountain-building processes.
The name of the eras of Greek origin, their meaning is as follows: Archean - the most ancient, Proterozoic - primary life, Paleozoic - ancient life, Mesozoic - middle life, Cenozoic - new life.
Archean - the most ancient era, began more than 3.5 billion years ago and lasted about 1 billion years. Little is known about life in the Archean, almost no traces of organic life remain: the sedimentary layers of the Archean age were strongly modified under the influence of high temperature and pressure. The presence of rocks of organic origin - limestone, marble indicates the existence of bacteria and blue-green algae in the Archean era.
In the Archean era, major aromorphoses occurred: the emergence of cells with a cell nucleus, the sexual process, photosynthesis and multicellularity.
Sexual process - expands the possibilities of natural selection, increases the possibility of adapting to environmental conditions due to the creation of countless combinations in chromosomes. The new method of reproduction, as useful in the conservation of species, was fixed by natural selection, and now it prevails in the animal and plant kingdoms.
The emergence of photosynthesis marked the beginning of the division of a single trunk of life into two - plants and animals - according to the method of nutrition and the type of metabolism. Saturation of water with oxygen, its accumulation in the atmosphere and the presence of food created the prerequisites for the development of animals in water, which protected living organisms from harmful ultraviolet radiation. Over time, ozone began to form in the atmosphere, absorbing almost all ultraviolet radiation - protecting life on the surface of water and land.
The emergence of a multicellular structure led to a complication in the organization of living beings: the differentiation of tissues, organs and systems, their functions. The paths of evolutionary transformations of the first multicellular organisms were different. Some moved to a sedentary lifestyle and turned into organisms such as sponges. Others began to crawl along the substrate with the help of cilia - flatworms. Still others have maintained a floating lifestyle. They acquired a mouth and gave rise to coelenterates.
Development of life in the Proterozoic era.
The Proterozoic era is the longest in the history of the Earth. It lasted about 2 billion years. On the border of the Archean and Proterozoic eras, the first great period of mountain building took place. It led to a significant redistribution of land and sea areas on Earth. These changes in the face of the Earth did not endure all types of organisms, many of them died out. Most of the fossil remains were destroyed, as a result of which so little is known about life in the Archean era.
During this era, bacteria and algae flourish exceptionally. An extremely intensive process of sedimentation proceeded with the participation of organisms. It is known that sedimentary iron is a waste product of iron bacteria. The Proterozoic includes the formation of the largest deposits of iron ores on Earth (Kursk, Krivoy Rog ores, iron ore of Lake Superior in the USA, etc.). The dominance of blue-greens is replaced by an abundance of green algae, including multicellular ones attached to the bottom. This required the dismemberment of the body into parts. The most important aromorphosis was the appearance of bilateral symmetry, which led to the differentiation of the body into the anterior and posterior ends, as well as the ventral and dorsal sides.
The anterior end is the place where the sense organs, nerve nodes, and later the brain develop. The dorsal side performs a protective function, in connection with which various skin glands, mechanical formations (bristles, hairs), protective coloration develop here. Most Proterozoic animals were multicellular. Not only lower multicellular organisms lived in the seas - sponges and radially symmetrical coelenterates; are also bilaterally symmetrical. Among the latter, annelids are known - molluscs and arthropods originated from them. By the end of the Proterozoic, the most ancient representatives of arthropods, the crustacean scorpions, appeared in the seas.
The accumulation of oxygen in the atmosphere led to the formation of an ozone screen in the atmosphere. The land is lifeless, but soil-forming processes have begun along the banks of water bodies as a result of the activity of bacteria and microscopic algae.
Development of life in the Paleozoic era.
The Paleozoic era is much shorter than the previous ones, it lasted about 340 million years. At the end of the Proterozoic, the land represented a single supercontinent, split into separate continents, grouped near the equator. This led to the creation of a large number of coastal areas suitable for the settlement of living organisms. By the beginning of the Paleozoic, some animals had an external organic or mineral skeleton. Its remains have been preserved in sedimentary rocks. That is why, starting from the first period of the Paleozoic-Cambrian, the paleontological record is quite complete and relatively continuous.
Periods:
Cambrian;
Ordovician;
Cambrian (80 20 Ma)
The climate of the Cambrian was temperate, the continents were low-lying. In the Cambrian, animals and plants inhabited mainly the seas. Bacteria and blue-green algae still lived on land.
Life in the Cambrian seas was most diverse and richly represented. Their area was larger than the area of modern seas. Almost all of Europe was under the sea. These seas were dominated by green and brown algae attached to the bottom; diatoms, aureus and euglena algae swam in the water column.
Among unicellular animals, there were numerous foraminifers - representatives of protozoa, which had a calcareous or shell glued from grains of sand. Sponges were very diverse. Along with sessile benthic animals, mobile organisms were also very diverse. Among them were bivalves, gastropods and cephalopods and annelids, from which arthropods had already evolved by the Cambrian. The most ancient arthropods - trilobites in body shape resembled modern crustaceans - wood lice. The body of trilobites was enclosed in a chitinous shell and dissected into 40-50 segments. The number of body segments in modern crustaceans is known to be much less.
Ordovician(5510 Ma)
In the Ordovician, significant areas of the Cambrian land subside, with the land area shrinking most in Siberia in North America. On the verge of the Cambrian and Ordovician, intense tectonic movements took place, which continued to the verge of the Ordovician and Silurian.
In the seas of the Ordovician, eukaryotes are very diverse - siphon green, brown and red algae. There is an intensive process of formation of reefs by corals. At the end of the Ordovician, the first land plants appear - psilophytes. They were preceded by aromorphosis, tissues appeared: integumentary with stomata, mechanical, supporting the plant in space, and conductive.
Further evolution of plants went in the direction of dividing the body into vegetative organs and tissues, improving the vascular system (ensuring the rapid movement of water to a great height). Psilophytes were transitional forms from the lower, avascular spores to the higher, vascular ones (lycopsids, horsetails, and ferns). They were transitional from aquatic to terrestrial plants. Their distribution on land was already prepared by the vital activity of prokaryotes, algae, fungi, which created the first soil.
Considerable diversity is observed among cephalopods and gastropods. Trilobites are very numerous. The diversity of foraminifera, sponges and some bivalves is decreasing.
In animals, a large aromorphosis occurs - the appearance of a grasping mouth apparatus, which caused a restructuring of the entire organization of vertebrates.. The ability to choose food contributed to the improvement of orientation in space by improving the senses. The first jaws did not have fins and moved in the water by snake-like movements. However, this method of movement, if necessary, to catch moving prey turned out to be ineffective.
Therefore, to improve movement in the water, skin folds were important, in the future certain parts of this fold develop further and give rise to fins, paired and unpaired. The appearance of paired fins - limbs - is the next major aromorphosis in the evolution of vertebrates. So, jawed vertebrates acquired prehensile mouthparts and limbs. In their evolution, they were divided into cartilaginous and bony fish.
Silurus(35 10 Ma)
As a result of intensive tectonic movements, the warm shallow seas of the Ordovician are replaced by significant land areas; significant climate desiccation was noted.
At the end of the Silurian, the development of peculiar arthropods - crustaceans - is observed. The flowering of cephalopods in the seas belongs to the Ordovician and Silurian (modern representatives of this class are squids, cuttlefish, octopuses). New representatives of invertebrates appear - corals (coelenterates), which begin to gradually replace sea urchins (echinoderms).
In the Silurian seas, the first representatives of vertebrates appear - the so-called armored fish. Their internal skeleton was cartilaginous, and outside the body was enclosed in a bony shell, consisting of scutes. Armored fish only in the shape of the body resembled real fish. They belonged to another class of vertebrates - jawless, or cyclostomes. They did not have true paired fins, they had one nostril (the modern representative of this class is the lamprey).
By the end of the Silurian is the beginning of the intensive development of land plants. The first land plants psilophytes - were deprived of true leaves, their structure is very similar to the structure of multicellular green algae, from which they originated. Ferns are growing.
The appearance of higher plants on land was prepared by the earlier release of bacteria and blue-green algae from the water, the presence of a biogenic layer of soil on land, from which psilophytes and ferns could draw food resources. In the development of mosses, ferns, horsetails, club mosses, the stage of motile flagellar gametes is preserved, for which an aquatic environment is required. Thus, the exit to land and separation from the aquatic environment of the Silurian plants were not yet final.
The accumulation of a large number of organic residues in the soil created prerequisites for the appearance on land of heterotrophic organisms using these organic substances. Indeed, non-chlorophyll heterotrophic organisms, fungi, appear in the Silurian.
The presence of significant reserves of plant biomass contributed to the emergence of animals on land. One of the first to move from the aquatic environment were representatives of the arthropod type - spiders.
Towards the end of the Silurian, the so-called Caledonian orogeny period began again. The mountains that arose during this period have survived to this day - these are the Scandinavian mountains, the ridges of the Sayano-Baikal mountain arc. Mountains of Scotland etc.
This mountain building again changed the contours of land and sea, changed the climate and the conditions for the existence of organisms.
Devonian(55 10 Ma)
As a result of the uplift of the land and the reduction of the seas, the Devonian climate was more sharply continental than in the Silurian. In the Devonian, glaciations were also observed in the mountainous regions of South Africa. In warmer regions, the climate changed towards greater desiccation, desert and semi-desert areas appeared.
In the seas of the Devonian fish reach great prosperity. Descendants of armored fishes give the most diverse representatives of real fishes. Among them were cartilaginous fish (modern representatives - sharks), and fish with a bone skeleton also appear. Among them, lungfish lived in shallow water bodies, in which, along with gill breathing, pulmonary respiration arose (the lung developed from the swim bladder), as well as lobe-finned fish, which were typically aquatic animals, but could breathe atmospheric air with the help of primitive lungs.
To understand the further evolution of fish, it is necessary to imagine the climatic conditions in the Devonian period. Most of the land was a lifeless desert. Along the banks of freshwater reservoirs, in dense thickets of plants, annelids and arthropods lived. The climate is dry, with sharp temperature fluctuations during the day and seasons. The water level in rivers and reservoirs often changed. Many reservoirs completely dried up and froze in winter. Aquatic vegetation died when water bodies dried up, plant residues accumulated and then rotted. All this created a very unfavorable environment for fish.
Under these conditions, only breathing atmospheric air could save them. Thus, the emergence of lungs can be considered as an idioadaptation to a lack of oxygen in the water. When water bodies dried up, animals had two ways of escape: burying themselves in silt or migrating in search of water. The lungfish, whose structure has hardly changed since the time of the Devonian, and which now live in shallow, drying water bodies of Africa, went along the first path. These fish survive the dry season by burrowing into the silt and breathing atmospheric air.
Only lobe-finned fish could adapt to life on land, due to the structure of paired fins. Until recently, it was believed that the crossopterans almost died out at the end of the Paleozoic and completely disappeared by the end of the Mesozoic. But in 1938, 1952 and in subsequent years, modern lobe-finned fish were caught off the coast of South Africa and Madagascar - real "living fossils" that have survived in a slightly modified form to this day.
At the end of the Devonian, the descendants of lobe-finned fish come to land, forming the first terrestrial class of vertebrates - amphibians or amphibians. The most ancient amphibians - stegocephals - were covered with a bone shell that dressed their heads, the shape of their bodies somewhat resembled newts and salamanders. Stegocephalians differed in a variety of sizes (from a few centimeters to 4 m in length). Stegocephalians combined the signs of fish, amphibians and reptiles. Stegocephalus - "combined" form. The reproduction of stegocephals, like all other amphibians, took place in the water. The larvae had gill breathing and developed in water.
On land, the first forests of giant ferns, horsetails and club mosses appear, psilophytes disappear. New groups of animals begin to conquer land. Representatives of arthropods that have acquired air breathing give rise to centipedes and the first insects.
The separation of amphibians from the aquatic environment was not yet final. They depended on the aquatic environment to the same extent as ferns. Therefore, the first terrestrial higher plants and animals could not conquer the inland land masses located far from water bodies.
At the end of the Devonian, a large aromorphosis occurs in plants - the appearance of a seed covered with a shell that protects it from drying out, a new group of gymnosperms arises. Interchangeable reproduction provides a number of advantages: the embryo is protected from adverse conditions by membranes, provided with food, and began to have a diploid number of chromosomes. In seed plants, fertilization occurs without the participation of water.
Carbon(65 10 Ma)
In the Carboniferous period, or Carboniferous, there was a noticeable warming and humidification of the climate. On the low continents, marshy lowlands are very common. Huge (up to 40 m high) ferns, horsetails and club mosses grew in hot, tropical swampy forests. In addition to these plants that reproduce by spores, gymnosperms, which arose as early as the end of the Devonian, begin to spread in the Carboniferous. The flowering of woody vegetation in the Carboniferous led to the formation of large seams of coal. This period includes the emergence of Donbass coals and the coal basin near Moscow.
In humid and warm marshy forests, the most ancient amphibians, stegocephals, reached exceptional prosperity and diversity. The first orders of winged insects appear - cockroaches, whose body length reached 10 cm, and dragonflies, some species of which had a wingspan of up to 75 cm.
Life in the seas of the Carboniferous did not differ significantly from that of the Devonian.
By the end of the Carboniferous, a slight rise in land begins, some drying up of the climate and cooling, unfavorable conditions for amphibians have been created. A certain group of amphibians turned out to be capable of further conquest of the land, which underwent very large changes that were useful in new conditions. The method of reproduction changed: internal fertilization arose: the egg had a large supply of yolk, a dense shell and an internal cavity with liquid, which protected the embryo from drying out. The development of the embryo took place in the egg on land.
Permian(50 10 Ma)
In the Permian, further land uplift led to the development of an arid climate and cooling. Wet and lush forests will mingle towards the equator, ferns are gradually dying out. They are replaced by gymnosperms. In their development, there are no flagellar stages, for the existence of which water is necessary. It was this adaptation that allowed gymnosperms to successfully withstand competition with spore plants in the Permian and displace them. Dying forests from ancient ferns formed the coals of Kuzbass and the Pechora-Vorkuta basin.
The drying up of the climate contributed to the disappearance of the amphibian stegocephalians. A significant part of large amphibians died out. Those that could hide in the remaining swamps and swamps gave rise to small amphibians. But the most ancient reptiles reach a significant diversity. Even in the Carboniferous, a group stood out among the stegocephalians, which had well-developed limbs and a mobile system of the first two vertebrae. Representatives of the group bred in the water, but went on land further than amphibians, fed on terrestrial animals, and then plants. This group is called cotylosaurs. Subsequently, reptiles and mammals descended from them.
Reptiles acquired properties that allowed them to finally break the connection with the aquatic environment. Internal fertilization and the accumulation of yolk in the egg made reproduction possible on land. The keratinization of the skin and the more complex structure of the kidney contributed to a sharp decrease in water loss by the body and a wide distribution. The chest provided a more efficient type of breathing - suction. The lack of competition caused the widespread distribution of reptiles over land and the return of some of them to the aquatic environment.
Questions of self-control
1. What hypotheses for the origin of life do you know?
2. What is the essence of the theory of panspermia?
3. Who proved that "the living can arise from the living"?
4. What is the geological age of the Earth?
5. Was the first stage on the way to the emergence of life on Earth?
6. Who proposed the coocervate theory?
7. What are coocervates?
8. Is it possible at the present stage of the emergence of life on Earth?
9. Read the study material below.
10. Answer the self-control questions.
Archean era- the most ancient, the earliest period in the history of the earth's crust. AT archean era the first living organisms arose. They were heterotrophs and used organic compounds as food. End archean era- the time of the formation of the earth's core and a strong decrease in volcanic activity, which allowed the development of life on the planet.
Archean era which began about 4 billion years ago lasted about 1.5 billion years. Archean era divided into 4 periods: Eoarchean, Paleoarchean, Mesoarchean, Neoarchean
Earth's crust
The lower period of the Archean era - Eoarchean 4 - 3.6 billion years ago
About 4 billion years ago the earth was formed as a planet. Almost the entire surface was covered with volcanoes and rivers of lava flowed everywhere. Lava, erupted in large quantities, formed continents and oceanic depressions, mountains and plateaus. Constant volcanic activity, exposure to high temperatures and high pressure led to the formation of various minerals: various ores, building stone, copper, aluminum, gold, cobalt, iron, radioactive minerals and others. Approximately 3.8 billion years ago the first reliably confirmed igneous and metamorphic rocks such as granite, diorite and anorthosite were formed on Earth. These rocks were found in a wide variety of places: on the island of Greenland, within the Canadian and Baltic shields, etc.
Approximately 2.8 billion years ago, the first supercontinent in the history of the Earth began to break apart.
| Heoarchean 2.8 - 2.5 billion years ago - the last period of the archean era, ending 2.5 billion years ago, is the time of formation of the main mass of the continental crust, which indicates the exceptional antiquity of the Earth's continents. Atmosphere and climate of the Archean era. At the beginning archean era there was little water on Earth, instead of a single ocean, there were only shallow pools that were not connected to each other. Atmosphere archean era, mainly consisted of carbon dioxide CO2 and its density was much higher than the current one. Due to the carbonic atmosphere, the water temperature reached 80-90°C. The nitrogen content was low, on the order of 10-15%. There was almost no oxygen, methane and other gases. The temperature of the atmosphere reached 120°C. |
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Flora and fauna of the Archean era
Archean era This is the time of the birth of the first organisms. The first inhabitants of our planet were anaerobic bacteria. The most important stage in the evolution of life on Earth is associated with the emergence of photosynthesis, which leads to the division of the organic world into flora and fauna. The first photosynthetic organisms were prokaryotic (pre-nuclear) cyanobacteria and blue-green algae. The eukaryotic green algae that then appeared released free oxygen from the ocean into the atmosphere, which contributed to the emergence of bacteria capable of living in an oxygen environment.
At the same time - on the border of the Archean Proterozoic era, two more major evolutionary events occurred - the sexual process and multicellularity appeared. Haploid organisms (bacteria and blue-greens) have one set of chromosomes. Each new mutation immediately manifests itself in their phenotype. If the mutation is beneficial, it is retained by selection; if it is harmful, it is eliminated by selection. Haploid organisms continuously adapt to the environment, but they do not develop fundamentally new features and properties. The sexual process dramatically increases the possibility of adapting to environmental conditions, due to the creation of countless combinations in the chromosomes.
Archean era (Archaean) - from 4.0 to 2.5 billion years ago
archean eon, archaean(ancient Greek ρχαος - ancient) - one of the four eons (the period of geological history during which the eonoteme was formed combines several eras) of the Earth's history, covering the time from 4.0 to 2.5 billion years ago.
The term archaea was coined in 1872 by the American geologist James Dana.
Archaean is divided into four eras (from latest to earliest):
neoarchean,
Mesoarchean,
paleoarchaean,
Eoarchaeus.
At that time, the Earth did not yet have an oxygen atmosphere, but the first anaerobic organisms appeared. During the same period, many currently existing deposits of sulfur, graphite, iron and nickel were actively formed.
Archaean and subsequent Proterozoic enter the time period Precambrian.
Hydrosphere and atmosphere. Climate
At the very beginning of the Archean era, there was little water on Earth; instead of a single ocean, there were only scattered shallow basins. The water temperature reached 70-90°C, which could only be observed if the Earth had a dense carbon dioxide atmosphere at that time. After all, of all possible gases, only CO2 could create an increased pressure of the atmosphere (for Archaean - 8-10 bar).
There was very little nitrogen in the atmosphere of the early Archean (10-15% of the volume of the entire Archean atmosphere), there was practically no oxygen at all, and gases such as methane are unstable and quickly decompose under the influence of hard solar radiation (especially in the presence of hydroxyl ion, also while arising in a humid atmosphere).
The temperature of the Archean atmosphere during the greenhouse effect reached almost 120°C. If, at the same pressure, the atmosphere in the Archaean consisted, for example, only of nitrogen, then surface temperatures would be even higher and reach 100 ° C, and the temperature during the greenhouse effect would exceed 140 ° C.
Approximately 3.4 billion years ago, the amount of water on Earth increased significantly and the World Ocean arose, overlapping the crests of the mid-ocean ridges. As a result, the hydration of the basaltic oceanic crust noticeably increased, and the growth rate of CO2 partial pressure in the Late Archean atmosphere somewhat decreased. The most radical drop in CO2 pressure occurred only at the turn of the Archean and Proterozoic after the release of the Earth's core and the associated sharp decrease in the Earth's tectonic activity.
Due to this, in the Early Proterozoic, the melting of oceanic basalts also sharply decreased. The basalt layer of the oceanic crust became noticeably thinner than it was in the Archaean, and under it the serpentinite layer formed for the first time - the main and constantly renewed reservoir of bound water on Earth.
Flora and fauna
There is no skeletal fauna in the Archean deposits, which serves as the basis for constructing the Phanerozoic stratigraphic scale; nevertheless, there are quite a lot of various traces of organic life here.
These include the waste products of blue-green algae - stromatolites, which are coral-like sedimentary formations (carbonate, less often silicic), and the waste products of bacteria - oncolites.
The first reliable stromatolites were discovered only at the turn of 3.2 billion years ago in Canada, Australia, Africa, the Urals and Siberia. Although there is evidence of the discovery of the remains of the first prokaryotes and stromatolites in sediments aged 3.8-3.5 billion years, in Australia and South Africa.
Also, in the siliceous rocks of the early Archean, peculiar filamentous algae were found, which are well preserved, in which details of the cellular structure of the organism can be observed. At many stratigraphic levels, there are the smallest rounded bodies (up to 50 m in size) of algal origin, which were previously taken for spores. They are known under the name "akritarch", or "spheromorphids".
The fauna of the Archean is much poorer than the flora. Separate indications of the presence of animal remains in the Archean rocks refer to objects that, apparently, are of inorganic origin (Aticocania Walcott, Tefemar kites Dons, Eozoon Dawson, Brooksalla Bassler) or are products of stromatolite leaching (Carelozoon Metzger). Many Archean fossils are not fully deciphered (Udokania Leites) or do not have an exact reference (Xenusion querswalde Pompecki).
Thus, prokaryotes of two kingdoms were reliably found in the Archean zone: bacteria, predominantly chemosynthetic, anaerobic and photosynthetic oxygen-producing cyanobionts. It is possible that the first eukaryotes from the kingdom of fungi, morphologically similar to yeast fungi, also appeared in the Archaean.
The oldest bacterial biocenoses, i.e. communities of living organisms, which included only producers and destructors, looked like mold films (the so-called bacterial mats) located at the bottom of reservoirs or in their coastal zone. Volcanic regions often served as oases of life, where hydrogen, sulfur and hydrogen sulfide, the main electron donors, came to the surface from the lithosphere.
Throughout almost the entire Archean era, living organisms were single-celled creatures that were highly dependent on natural factors. And only at the turn of the Archean and Proterozoic two major evolutionary events occurred: the sexual process and multicellularity appeared.
Haploid organisms (bacteria and blue-green algae) have one set of chromosomes. Each new mutation immediately manifests itself in their phenotype. If the mutation is beneficial, it is preserved by natural selection; if it is harmful, it is eliminated.
Haploid organisms continuously adapt to the environment, but they do not develop fundamentally new features and properties. The sexual process dramatically increases the possibility of adapting to environmental conditions, due to the creation of countless combinations in the chromosomes.
Diploidy, which arose simultaneously with the formed nucleus, makes it possible to preserve mutations and use them as a reserve of hereditary variability for further evolutionary transformations.
The Archean era is the most ancient, the earliest period in the history of the earth's crust. In the Archean era, the first living organisms arose. They were heterotrophs and used organic compounds as food. The end of the Archean era is the time of the formation of the earth's core and a strong decrease in volcanic activity, which allowed the development of life on the planet.
Earth's crust Lower period of the Archean era - Eoarchean 4 - 3.6 billion years ago About 4 billion years ago the earth was formed as a planet. Almost the entire surface was covered with volcanoes and rivers of lava flowed everywhere. Lava, erupted in large quantities, formed continents and oceanic depressions, mountains and plateaus. Constant volcanic activity, exposure to high temperatures and high pressure led to the formation of various minerals: various ores, building stone, copper, aluminum, gold, cobalt, iron, radioactive minerals and others. Approximately 3.8 billion years ago the first reliably confirmed igneous and metamorphic rocks such as granite, diorite and anorthosite were formed on Earth. These rocks were found in a wide variety of places: on the island of Greenland, within the Canadian and Baltic shields, etc.
The next period of the Archean era is Paleoarchean 3.6 - 3.2 billion years ago. It is the time of the formation of the first supercontinent in the history of the Earth - Valbaru and the unified World Ocean, which changed the structure of the crests of oceanic ridges, which led to the process of increasing the amount of water on Earth, and the amount of CO2 in the atmosphere began to decrease.
Atmosphere and climate of the Archean era At the very beginning of the Archean era, there was little water on Earth, instead of a single ocean, there were only shallow pools that were not connected to each other. The atmosphere of the Archean era consisted mainly of carbon dioxide CO2 and its density was much higher than the current one. Due to the carbonic atmosphere, the water temperature reached 80-90°C. The nitrogen content was low, on the order of 10-15%. There was almost no oxygen, methane and other gases. The temperature of the atmosphere reached 120°С
Flora and fauna of the Archean era The Archean era is the time of the birth of the first organisms. The first inhabitants of our planet were anaerobic bacteria. The most important stage in the evolution of life on Earth is associated with the emergence of photosynthesis, which leads to the division of the organic world into flora and fauna. The first photosynthetic organisms were prokaryotic (pre-nuclear) cyanobacteria and blue-green algae. The eukaryotic green algae that then appeared released free oxygen into the atmosphere from the ocean, which contributed to the emergence of bacteria capable of living in an oxygen environment. At the same time - on the border of the Archean Proterozoic era, two more major evolutionary events occurred - the sexual process and multicellularity appeared. Haploid organisms (bacteria and blue-greens) have one set of chromosomes. Each new mutation immediately manifests itself in their phenotype. If the mutation is beneficial, it is retained by selection; if it is harmful, it is eliminated by selection. Haploid organisms continuously adapt to the environment, but they do not develop fundamentally new features and properties. The sexual process dramatically increases the possibility of adapting to environmental conditions, due to the creation of countless combinations in chromosomes.
The most ancient remains of organisms and the substances created with their participation have come down to us from the Archean deposits of the earth's crust.
These deposits are extremely powerful (thick): it is clear that hundreds of millions of years passed while they accumulated. The most ancient, lower deposits, squeezed by the enormous weight of the overlying layers, have changed greatly: from layered, they have turned into crystalline. In addition to pressure, this was also helped by the action of the internal heat of the globe. The remains of organisms that could be in them, while also changed beyond recognition. We would not even know whether there was life then or not, if not for some substances accumulated in the Archean layers; these substances, as we well know, can be formed in the earth's crust only through the action of organisms. They really formed from the remains of ancient plants and animals. But we do not find these remnants themselves in the crystalline rocks of the Archean period.
The situation is better with those Archean deposits that have come down to us in the form of layered rocks that have not yet had time to recrystallize. These are the younger layers. They found the remains of bacteria that looked like microscopically small balls. The remains of other bacteria, the so-called iron bacteria, whose relatives still live on Earth, have been preserved. Iron bacteria perform a huge chemical work, taking part in the creation of iron ores. They live in those waters that contain salts (nitrous) of iron, and are surrounded by the thinnest filamentous tubes that have arisen from the mucus they secrete; they extract salts (nitrous) of iron from water, process them in their tiny body and impregnate tubes with them (turning them into oxide salts). These bacteria live in colonies. When the tubules are completely saturated with iron, the bacteria leave them and begin to build new tubules. As a result of their activity, iron compounds accumulate, which, after hundreds of thousands and millions of years, turn into powerful deposits of iron ores.
Bacteria play a huge role in the life of the Earth. Even Pasteur did not quite grasp it. Bacteria win for themselves more and more new food sources; they filled the soil, water and air. One gram of forest soil contains about 3 billion bacteria; even in a gram of sandy soil there are about 1 billion of them.
They inhabit the seas in great numbers. In the depths of the Black Sea there are huge accumulations of hydrogen sulfide, making life here impossible for plants and animals. This hydrogen sulfide, however, does not penetrate the surface layers of the water, and therefore life flourishes in these seas down to a depth of 200 meters. Where does hydrogen sulfide go? It turns out that it is captured by sulfuric bacteria that live at a depth of 200 meters and process it into sulfuric acid compounds. Approximately the same picture is observed in the Caspian Sea. How many bacteria work in such a giant chemical laboratory? Their number is unimaginable.
Since bacteria can adapt to the most diverse conditions of life, they could give rise to other groups of organisms. From them, indeed, some algae got their origin. The transition from bacteria to algae was a big step forward in evolution. True, algae, for the most part, still belong to the world of microscopically small creatures, but they have a more definite organization and belong to more complex creatures, along with the simplest animal organisms. Like bacteria, single-celled plants and animals swarm everywhere on earth, and they were first discovered by Leeuwenhoek in stagnant water. In the unicellular bodies of these beings we find a division into protoplasm and nucleus; in addition, they often have a protective shell or a kind of skeleton, sometimes striking in the subtlety and elegance of the structure.
In the body of algae, in addition to the nucleus, there is another important formation, which is already characteristic of all typical plants. This is the so-called pigment, a coloring matter concentrated in special grains (sometimes in the surface layers of protoplasm). Not all algae have the same pigment. According to its color, several groups of algae are distinguished: blue-green, green, crimson, brown.
A special group among algae are flagella. These are unicellular organisms equipped with a movable flagellum, thanks to which they move through the water. They stand at the boundary of the plant and animal worlds. Some of them have a pigment spot and are classified as algae, others are devoid of pigment and are able to capture food, which they digest. These are the simplest animals.
The green pigment characteristic of a plant cell, the so-called chlorophyll, is a special substance that captures the energy of sunlight and uses it for chemical activity. This activity consists, firstly, in the splitting of carbon dioxide in the air into its constituent parts - carbon and oxygen, and secondly, in performing creative work: in building organic compounds - sugar, starch, and other carbohydrates - from released carbon and water. , fats and protein bodies. All these complex chemicals arise in the plant cell from inorganic substances due to the activity of chlorophyll. Another released component of carbon dioxide - oxygen - goes back into the air in its pure form. The air is thus constantly replenished with oxygen.
Recall that animals eat only ready-made complex organic compounds - carbohydrates, fats and proteins. Animals cannot prepare these compounds for themselves. They get them from the plant world. Without plants, animals would die of starvation. Therefore, animals could appear on Earth only after the appearance of plants. Plants have prepared a supply of nutrients for them. In addition, they created another condition necessary for animal life. Animals need not only food, but also breathing. And for that they need oxygen. Currently, the air, as we know, contains about 21% oxygen. Its quantity is constant, and this constancy is maintained by the activity of plants, which continuously enrich the air with oxygen. Not so in the Archean era.
The composition of the atmosphere in the early days of the earth's life, as we have already pointed out earlier, apparently differed sharply from the present. First, there was almost no oxygen in the air; secondly, the air then contained a lot of carbon dioxide. This gas made the air impervious to sunlight; therefore, the heating by the sun was not too strong. But the presence of this gas and water vapor in the air greatly delayed the cooling of the air at night. The earth was, as it were, enveloped in a shell that was hardly permeable to heat, which retained its own earthly heat and increased the average temperature of the earth. One scientist calculated that if the amount of carbon dioxide in the air were now tripled, the average temperature on Earth would rise by almost 10 degrees. This rise would be more than sufficient to melt the ice in the polar regions and to remove the snow from the high mountain peaks. The Earth's climate would have to change drastically: prolonged frosts would occur only occasionally, winters would be shortened, summers would become longer and hotter; in general, in our places the climate would be the same as we find now, for example, in our Transcaucasia. And in the far north, where the permafrost region now extends, a rather mild temperate climate would be established.
There is every reason to think that in the Archean era the climate was even much warmer, both due to the high content of carbon dioxide in the air, and due to the fact that the Earth had not yet squandered its original heat, and, finally, due to the fact that the Sun itself shone dazzlingly white. light and sent hotter rays to Earth. Life flourished in the warm waters of the then seas and oceans. New forms of the plant world were created, and as a result of the work of plants, the earth's atmosphere began to be gradually cleansed of carbon dioxide and enriched with oxygen. Oxygen in dissolved form also appeared in the sea. This created the conditions under which animal life became possible. It arose after the plant.
However, we know even less about the animals of the Archean era than about plants. In some places, shells of unicellular animals, the so-called rootlets, have been preserved. Apparently, animals in those days still played a small role in the life of the Earth. Of greater interest are other forms of life that arose in the Archean era, and perhaps even earlier.
Modern science is more interested in the smallest organisms than in the large ones. Not elephants or whales are the focus of scientists, but the smallest, barely visible or completely invisible living particles. Practical life requires the most detailed study of precisely these smallest organisms. The discovery and study of them can serve to explain the mysterious nature of many diseases: after all, many diseases are based on an attack on a person by microscopic or ultramicroscopic organisms. In agriculture, the properties of these creatures are associated with issues of increasing productivity and increasing soil fertility. Science is occupied with the study of these negligibly small beings and in the hope of approaching the solution of the question of the first stages of evolution and the beginning of life.
At the edge of our knowledge are organisms that are so small that the best modern ultramicroscopes are powerless to make them visible. They pass (filter) through the finest filters and cannot be trapped and separated from other substances to make them more accessible to study. It is natural to ask how it was possible to know about their existence if they elude our most advanced instruments? Although they themselves are invisible, we can both see and study their actions. The smallest of the "filtering creatures" are called bacteriophages. We become aware of their presence because they devour or destroy living bacteria. Science has not yet established a final view of the nature of these bacteriophages. Many scientists consider them the simplest of all living organisms. Others are more inclined to see them not as organisms, but as chemicals. But whatever their nature, it is clear that here we are dealing with particles that stand on the border of the living and non-living world.
Somewhat larger than bacteriophages are ultramicroscopic creatures called viruses (the word "virus" is Latin and in Russian means "poison").
These viruses cause a number of severe diseases in humans, animals and plants. Hoof disease of cattle and pigs, canine distemper, smallpox, typhus, yellow fever, rabies, measles and influenza in humans, a number of diseases of potatoes, tobacco and other plants are caused by the presence of viruses. Although they are larger than bacteriophages, they are still so small that they freely pass through filters, for which they received their name "filterable viruses".
It is possible that bacteriophages and viruses are the remains of ancient organisms. They also changed during the history of the Earth, adapting to the existence in new conditions. Bacteriophages developed the ability to fight bacteria, viruses began to destroy plants and animals. But for all that, they have not even risen to the same level of organization as the bacteria. Therefore, in them one can see the remains of primary organisms that existed in the Archean era.
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