Brief history of the development of the organic world. Archean Era
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 meteorite showers, the formation of volcanic craters and the earth's crust. Active formation of the hydrosphere begins, salty reservoirs with hot water isolated from each other appear. 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. Vaalbara, the main terrestrial continent, is being formed.
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 plant species are unicellular filamentous algae - spheromorphids - the habitat of bacteria. When these algae form in colonies, they can be seen without special instruments. They can go free swimming or attach themselves to the surface of something. In the future, algae will form a new form of life - lichens.
During the Archean era, the first prokaryotes- single-celled organisms that do not have a nucleus. 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.
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
In the early period, there was little water on earth. The water temperature during the Archean era reached 90°C. This indicates the saturation of the atmosphere with carbon dioxide. There was very little nitrogen in it, there was almost no oxygen in the early stages, the remaining gases are quickly destroyed under the influence of sunlight. The 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 water and air temperature 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. On the territory of the Russian Federation, Archean deposits have been found in the Urals and Siberia.
In details periods of the archean era will be discussed in the next lectures.
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 oldest period of the earth's existence, covering the time interval from 4 to 2.5 billion years ago, is called the "Archaean era". The flora and fauna were just beginning to emerge, there was very little oxygen on Earth, and of the water bodies on the planet there was only one shallow ocean, consisting of several reservoirs with saturated salt water, while there was no mountain landscape and depressions at all. This is the period of the beginning of the formation of mineral deposits: graphite, nickel, sulfur, iron and gold.
At that time, the rays of sunlight could not yet penetrate the hydrosphere and atmosphere mixed together, which constituted a single shell of steam and gas. The resulting greenhouse effect prevented the sun from touching the ground.
The Archean era was named so by the American scientist J. Dana in 1872. The term "archean" from ancient Greek means "ancient". The Archean is divided into four main eras, ranging from the most ancient, the Eoarchean, to the Neoarchean. Let's dwell on them in more detail.
Beginning of the Archean - Eoarchean
The 400 Ma period began about 4 billion years ago. The Eoarchean is characterized by the frequent fall of meteorites and the formation of craters. The lava covering the surface of the planet gradually began to give way to the earth's crust, which was actively forming.
The Archean era in this time period is known for laying the oldest rocks, the largest formations of which were found in Greenland. Their age is approximately 3.8 billion years.
The formation of the hydrosphere was just beginning. And although the oceans had not yet appeared, there were already hints of the first small water formations. With their characteristic isolation from each other, with concentrated salty and very hot water.
There was little oxygen and nitrogen in the atmosphere, a significant part of it was carbon dioxide. The temperature in the air shell of the Earth reached 120 °C.
The first organisms of the Archean era began to appear just then. These were cyanobacteria that left behind ancient stromatolites - waste products. These microorganisms produce oxygen through photosynthesis, being the most ancient form of life on the planet.
The most important moment in the Eoarchean is the beginning of the formation of the first terrestrial continent - Vaalbara.
Second era - paleoarchaean
The Archean era of this period covers a time interval of 200 million years, which began 3.6 billion years ago. Then the day had a duration of no more than 15 hours. The formation of the main continent was coming to an end, the still shallow World Ocean appeared. The Earth's core has become more solid, which has strengthened the Earth's magnetic field almost to the current level.
It is this period that allows us to assert that already at that time the first living organisms appeared. It is known for sure that the remains of their waste products, found today, date back to the Paleoarchean.
Animals of the Archean era are the first bacteria, organisms that contributed to the formation of the Earth's atmosphere through photosynthesis, creating conditions for the development of new forms of life.
Mesoarchean: the split of Vaalbara
Mesoarchean - a period that lasted 0.4 billion years (began 3.2 billion years ago). It was then that the split of Vaalbara occurred, which was divided at an angle of 30 ° into two separate parts. And also appeared from a collision with an asteroid, the most famous crater in our time in Greenland. Perhaps during the Mesoarchean period, the first glaciation, the Pongolian, also occurred on Earth.
The development of life in the Archean era of the Mesoarchean period was characterized by an increase in the number of cyanobacteria.
The final stage - neoarchaean
The Neoarchean ended 2.5 billion years ago. It is characterized by the completion of the formation of the earth's crust, as well as the release of a large amount of oxygen, which subsequently led (at the beginning of the next era) to an oxygen catastrophe. It was then that the Earth's atmosphere completely changed - oxygen began to predominate in its composition.
Volcanic activity developed rapidly, which contributed to the formation of rocks and precious metals and stones. Granites, syenites, gold, silver, emeralds, chrysoberyls - all this and much more appeared several billion years ago, in the Neoarchean.
What else is interesting about the Archean era? The flora and fauna at that time formed the oldest deposits of minerals that are widely used today. Also, this was influenced by the unstable situation on the planet. Forming landscapes, the earth's crust and the first mountain formations were destroyed under the influence of ocean waters and the spill of volcanic lava.
Animal world
Scientists say that the origin of life began precisely in the Archean period. And although these forms were too small, they still represented real living microorganisms, the first bacteriological communities that left their mark on the planet in the form of fossilized stromatolites.
It was established that it was the bacteria that made a significant contribution to the formation of nanocrystals of arogonite, a mineral based on calcium carbonate. Aragonite is part of the surface layer of the shells of modern molluscs and is contained in the exoskeleton of corals.
Cyanobacteria became the culprits of the occurrence of deposits of not only carbonate, but also siliceous sedimentary formations.
The Archean era is characterized by the appearance of the first prokaryotes - pre-nuclear unicellular organisms.
Characteristics of prokaryotes
Living organisms do not have a formed nucleus, but they are a complete cell. Prokaryotes produce oxygen through photosynthesis. The DNA information (nucleotide) that a cell carries is not packaged in the protein shell of the nucleus (histone).
The group is divided into two domains:
- bacteria.
- Archaea.
Archaea
Archaea are the oldest microorganisms, like prokaryotes, which do not have a nucleus. However, their structure of life organization differs from that of other types of microbes. In appearance, archaea are similar to bacteria, but some of them have an unusual flat or square shape.
There are five types of archaea, despite the fact that it is quite difficult to classify them. It is impossible to grow archaebacteria in nutrient media, therefore all studies are carried out only on the basis of samples taken from their habitat.
These microorganisms can use both sunlight and carbon as an energy source, depending on the species. Archaea do not form spores and reproduce asexually. They are not pathogenic for humans, they can survive in the most extreme conditions: the ocean, hot springs, soil, salt lakes. The most numerous species of archaea makes up a significant part of the plankton in the oceans, which serves as food for marine animals.
Some species even live in the intestines of humans, helping to carry out the processes of digestion. Archaea are used to create biological gas, clean sewers, and sedimentation tanks.
Plants
As you can understand, the Archean era, the plant world of which was a little richer than the animal world, is not characterized by the presence of vertebrates, fish, and even multicellular algae. Although the beginnings of life have already appeared. As for the flora, scientists have found that the only plants at that time were filamentous algae, in which, by the way, bacteria lived.
And blue-green algae, previously erroneously considered plants, turned out to be colonies of cyanobacteria that use both carbon and oxygen as a resource to sustain life and are not part of the Archean plant world.
filamentous algae
The Archean era was marked by the appearance of the first plants. They are unicellular filamentous algae which are the simplest form of flora. They do not have a specific shape, structure, organs and tissues. Forming colonies, they become visible to the naked eye. This is mud on the surface of the water, phytoplankton in its depths.
The cells of filamentous algae are connected into a single thread, which may have branches. They can easily both float freely and attach to various surfaces. Reproduction occurs by dividing the thread into two separate ones. Both all threads, and only extreme, or main ones, can be capable of division.
Algae do not have flagella, they are interconnected by microscopic cytoplasmic bridges (plasmodesmata).
In the course of evolution, algae formed another form of life - lichens.
The Archean era is the first period when biological life appeared on Earth almost out of nothing. This is a turning point in the history of the evolution of the planet, characterized by the emergence of conditions for the emergence of flora and fauna: the formation of the earth's crust, the oceans, the atmosphere, suitable for other more complex forms of flora and fauna.
The end of the Archaean marked the beginning of the development of the sexual process of reproduction in bacteria, the appearance of the first multicellular microorganisms, some of which later became terrestrial organisms, others acquired signs of waterfowl and settled in the ocean.
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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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. .).
| Period, duration, million years | Climate and geological processes | Animal world | plant world | The most important aromorphoses |
|---|---|---|---|---|
| Cenozoic, 66 Ma | ||||
| Anthropogen, 1.5 | Repeated changes of warming and cooling. Large glaciations in the middle latitudes of the Northern Hemisphere | Modern animal world. Evolution and domination of man | Modern flora | Intensive development of the cerebral cortex; upright posture |
| Neogene, 23.0 Paleogene, 41±2 |
Uniform warm climate. Intensive mountain building. The movement of the continents, the Black, Caspian, Mediterranean Seas are isolated | Mammals, birds, insects dominate; the first primates appear (lemurs, tarsiers), later parapithecus and dryopithecus; many groups of reptiles, cephalopods disappear | Flowering plants, especially herbaceous ones, are widely distributed; the flora of gymnosperms is reduced | |
| Mesozoic, 240 Ma | ||||
| Cretaceous (chalk), 70 | Cooling of the climate, increase in the area of the World Ocean | Bony fish, first birds, and small mammals predominate; placental mammals and modern birds appear and spread; giant reptiles die out | Angiosperms appear and begin to dominate; ferns and gymnosperms are reduced | Emergence of flower and fruit. The appearance of the uterus |
| Jurassic (Jurassic), 60 | At first, the humid climate changes to arid one at the equator. | Giant reptiles, bony fish, insects, and cephalopods predominate; Archeopteryx appears; ancient cartilaginous fish die out | Modern gymnosperms dominate; ancient gymnosperms die out | |
| Triassic (Triassic), 35±5 | Weakening of climatic zonality. The beginning of the movement of the continents | Amphibians, cephalopods, herbivorous and predatory reptiles predominate; bony fish, oviparous and marsupial mammals appear | Ancient gymnosperms predominate; modern gymnosperms appear; seed ferns are dying out | The appearance of a four-chambered heart; complete separation of arterial and venous blood flow; the appearance of warm-bloodedness; appearance of the mammary glands |
| Paleozoic, 570 Ma | ||||
| Permian (Perm), 50±10 | Sharp climate zoning, completion of mountain building processes | Marine invertebrates, sharks dominate; reptiles and insects develop rapidly; there are animal-toothed and herbivorous reptiles; stegocephalians and trilobites are dying out | Rich flora of seed and herbaceous ferns; ancient gymnosperms appear; tree-like horsetails, club mosses and ferns die out | Pollen tube and seed formation |
| Carbon (carbon), 65±10 | Distribution of forest swamps. The uniformly humid warm climate is replaced at the end of the period by arid | Amphibians, mollusks, sharks, lungfish dominate; winged forms of insects, spiders, scorpions appear and develop rapidly; the first reptiles appear; trilobites and stegocephals are noticeably reduced | An abundance of tree-like, fern-like, forming "coal forests"; seed ferns appear; psilophytes disappear | The appearance of internal fertilization; the appearance of dense egg shells; keratinization of the skin |
| Devonian (Devonian), 55 | Change of dry and rainy seasons, glaciation in the territory of modern South Africa and America | Armored, molluscs, trilobites, corals prevail; lobe-finned, lung-breathing and ray-finned fish, stegocephals appear | Rich flora of psilophytes; mosses, ferns, mushrooms appear | The dismemberment of the body of plants into organs; transformation of fins into terrestrial limbs; the emergence of respiratory organs |
| Silurian (Silur), 35 | Initially dry, then humid climate, mountain building | Rich fauna of trilobites, molluscs, crustaceans, corals; armored fish appear, the first terrestrial invertebrates: centipedes, scorpions, wingless insects | Abundance of algae; plants come to land - psilophytes appear | Differentiation of the plant body into tissues; division of the animal body into sections; formation of jaws and limb girdles in vertebrates |
| Ordovician (Ordovician), 55±10 Cambrian (Cambrian), 80±20 |
Glaciation is replaced by a moderately humid, then dry climate. Most of the land is occupied by the sea, mountain building | Sponges, coelenterates, worms, echinoderms, trilobites predominate; jawless vertebrates (scutes), molluscs appear | Prosperity of all departments of algae | |
| Proterozoic, 2600 Ma | ||||
| — | The surface of the planet is bare desert. Frequent glaciations, active rock formation | Protozoa are widespread; all types of invertebrates, echinoderms appear; primary chordates - subtype Cranial | Bacteria, blue-green and green algae are widespread; red algae appear | The emergence of bilateral symmetry |
| Archean, 3500 (3800) Ma | ||||
| — | Active volcanic activity. Anaerobic living conditions in shallow water | The emergence of life: prokaryotes (bacteria, blue-green algae), eukaryotes (green algae, protozoa), primitive metazoans | Emergence of photosynthesis, aerobic respiration, eukaryotic cells, sexual process, multicellularity | |
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 a mandatory 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 began to be 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:
- a long duration of ontogenesis, since in the course of the individual development of the organism, some cells are replaced by others;
- numerous offspring, since the organism can allocate more cells for reproduction;
- 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) various types of living organisms appeared, 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(“the era of 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 high 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 heyday (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. In the Cretaceous period, 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 in the development of the biosphere.
