general characteristics Archean era
Archean is the oldest era, the upper limit of which is about 2.5 billion years ago, and the lower limit is 3.8-4 billion years ago.
The duration of the Archean era is approximately 1.5 billion years. During this time, the primary continental crust completes its formation, and mountainous relief of volcanic origin appears.
The landmass are represented by Gondwanaland and Laurasia.
The atmosphere has a low density and consists of ammonia, hydrogen, methane, hydrogen sulfide, water vapor, carbon monoxide and carbon dioxide. There is no oxygen in it.
Experts suggest that the water in the ocean at that time was slightly brackish. Climatic zonation was already evident.
The rocks exposed on the surface of the continents are of Archean age, but their recognition is complicated by the fact that the outcrops of these rocks cover thick strata of younger rocks.
Even in places where they are exposed, it is impossible to determine their original character, because they are highly metamorphosed.
In addition, ancient rocks were melted and destroyed during magmatic intrusions, which means that to this day traces of the primary earth's crust not detected.
Large areas of exposure of Archean rocks to the surface are known within North America, these are:
- The Canadian Shield, located on both sides of Hudson Bay;
- Rocky Mountains.
Archean rocks of the Canadian Shield are in some places overlain by younger rocks. The oldest rocks known are marble, slate and crystalline schist.
The limestones and shales were sealed by lava. Later they were subjected to powerful tectonic movements and strong metamorphism.
As a result of long-term denudation, in some places they came to the surface.
Archean rocks in the Rocky Mountains form the crests of individual peaks, such as Pikes Peak and many mountain ranges.
There are Archean outcrops of rocks within Sweden, Norway, Finland, Russia - these are metamorphosed sedimentary rocks and granites. Archean rocks are found in the south and southeast of Siberia, China, western Australia, Africa, and the northeastern part of South America.
In Archean rocks of South Africa and in the province of Ontario in Canada, traces of colonies of unicellular blue-green algae and traces of bacterial activity were found.
Archean climate
The prevailing view among 19th-century scientists was that the temperature on the Earth's surface in ancient eras was maintained mainly by internal heat.
In all likelihood, this was true for the earliest stages of the development of the planet - lunar and nuclear. But, in the Archean era, the atmosphere and hydrosphere already existed and, in the distribution of heat on the earth's surface, the leading role was to be played by the energy of the Sun.
If this is accepted as true, then in the Archean there was climatic zonation, because The amount of solar heat is related to the latitude of the place.
Some evidence of climatic zonation is confirmed, however, by isolated facts - these are the finds of ancient metamorphosed glacial deposits - tillites.
Their remains were found in North America, Central and South Africa, in southern Australia and Siberia.
Unfortunately, scientists have not yet been able to determine their centers, as well as the direction of movement of these glaciers.
In North America, traces of glaciers can be traced north of the modern 42nd latitude parallel by almost 1850 km and north by 370 km.
The thickness of the Early Proterozoic tillites was found to reach 160-180 m.
Tillite horizons are interbedded with clay shales, and their accumulation took place in lacustrine or river conditions.
Note 1
Thus, there was an alternation of glacial and interglacial eras.
At this time, the size of glaciers was shrinking, and lakes of glacial origin took their place.
Ancient glaciation, according to N.M. Strakhov, had a mountain character.
In all likelihood, the glaciers of modern Antarctica did not yet exist in the Archean and Proterozoic, because there were no vast continental masses.
Ancient glaciers may have covered the tops of some mountains and descended in tongues to the foothills.
Associated with glacial deposits are metamorphosed organic remains—graphite schists. The presence of this primitive vegetation in the ancient oceans suggests that in certain areas of the planet the climate was relatively warm.
The temperature of the atmosphere itself, according to scientists, could reach 120 degrees.
Note 2
The data is very scarce, but, nevertheless, they allow us to conclude that climatic zonation existed on Earth 2-3 billion years ago, but scientists practically do not know which belts existed and where they passed.
Flora and fauna of the Archean
There are four eras in the Archean era:
- Eoarchaean;
- paleoarchaean;
- Mesoarchaean;
- Neoarchaean.
Eoarchaean, lasting 400 million years, is the beginning of the Archean era. Meteorites fall on the Earth, craters are formed, and the active formation of the earth's crust and hydrosphere is underway.
There is still negligibly little oxygen and nitrogen in the earth's atmosphere, but a significant part belongs to carbon dioxide. It was under these conditions that the first organisms appeared - cyanobacteria, leaving behind waste products that produced oxygen through photosynthesis.
In the Eoarchean, the formation of the first earthly continent, Vaalbara, took place.
The second, Paleoarchean era lasted 200 million years. The formation of the first continent was completed, and another shallow ocean appeared. The length of the day at this time was 15 hours. The Earth's magnetic field strengthened because the core became more solid.
Scientists believe that at this time the first living organisms appeared - the first bacteria.
In the Mesoarchean, which lasted 0.4 billion years, the Vaalbara split occurred. The modern crater in Greenland appeared precisely then as a result of a collision with an asteroid. Perhaps at this time the first Pongol glaciation began on the planet.
In the Mesoarchean, the number of cyanobacteria increases.
The Archean era ends with the Neoarchean 2.5 billion years ago.
By this time, the formation of the earth's crust is completed, the release of large quantity oxygen. The Earth's atmosphere at this time completely changed and oxygen became the predominant gas.
As a result of violent volcanic activity, precious metals and stones were formed. The animal forms are very small, but nevertheless they were real living microorganisms.
Carbonate and siliceous sedimentary rocks were created by cyanobacteria.
At this time, the first prokaryotes—prenuclear unicellular organisms—appear.
At the end of the Archaean, the sexual process of reproduction in bacteria begins, and the first multicellular microorganisms appear.
Subsequently, some of them became terrestrial organisms, while the other part acquired characteristics of waterfowl and settled in the water.
Note 3
The Archean era as a whole is the most ancient period in the life of the Earth, at this time photosynthesis appeared, the separation of flora and fauna occurred, and the outlines of continents and oceans were formed. An important point was the accumulation of oxygen, which changed the structure of the planet’s air envelope and gave rise to new chemical processes.
Archean era- this is the first stage in the development of life on earth, spanning a time interval of 1.5 billion years. It originates 4 billion years ago. During the Archean era, the flora and fauna of the planet began to emerge, and the history of dinosaurs, mammals and humans began from here. The first deposits of natural resources appear. There were no mountain heights and no ocean, 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.
Archean era translated 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. The active formation of the hydrosphere begins, salty reservoirs isolated from each other appear with hot water. Prevails in the atmosphere 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 covers a period of time of 200 million years. The Earth's magnetic field is strengthened by increasing the hardness of the earth's core. This has a beneficial effect on the living conditions and development of simple microorganisms. A day lasts about 15 hours. The formation of the world's oceans takes place. Changes in underwater 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 earth's 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 splits into two parts. As a result of a sharp cooling of the planet, which is caused by constant volcanic processes, the Pongol glacial formation is formed. During this period, the number of cyanobacteria begins to actively grow. Chemolithotrophic organisms develop that do not require oxygen and sunlight. Vaalbar is fully formed. Its size is approximately equal to the size of modern Madagascar. The formation of the continent of Ur begins. Large islands slowly begin to form from volcanoes. The atmosphere, as before, is 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, and the level of oxygen in the atmosphere increases. The continent of Ur becomes the basis of Kenorland. Most planets are occupied by volcanoes. Their active work leads to increased formation of minerals. Gold, silver, granites, diorites and others, no less important natural resources, were formed during the Neoarchean period. IN last centuries Archean era appear first multicellular organisms, which were later divided into terrestrial and sea inhabitants. Bacteria begin to develop the sexual process of reproduction. Haploid microorganisms have one chromosome set. They constantly adapt to changes in their environment, but at the same time they do not develop 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 to the surface of something. Later the algae will form new uniform life - lichens.
During the Archean era the first prokaryotes- single-celled organisms that do not have a nucleus. Through photosynthesis, prokaryotes produce oxygen and create favorable conditions for the emergence of new life forms. 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 into one group is considered outdated. Externally, 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 digestive processes. Other types are used to clean sewage ditches and ditches.
There is a theory, unconfirmed by facts, that during the Archean era the birth and development of eukaryotes - microorganisms of the fungal kingdom, similar to yeasts - 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 find out anything about climatic zones of this period. The existence of zones of different climates in the Archean era can be judged by ancient glacial deposits - tillites. Remains of glaciations have been found in America, Africa, and Siberia today. It is not yet possible to determine their true size. Most likely, glacial deposits covered only mountain peaks, because vast continents had not yet been formed during the Archean era. 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 atmospheric temperature reaches 120 degrees. If nitrogen predominated 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 noticeably. The temperature of water and air also dropped. And the amount of oxygen increased. Thus, the planet gradually became suitable for life of various organisms.
Archean minerals
It was during the Archean era that the greatest formation of minerals occurred. 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 down by this era of the earth's life. In the territory Russian Federation Archean deposits were found in the Urals and Siberia.
In details periods of the Archean era will be discussed in subsequent lectures.
The oldest period of the earth's existence, covering the time period from 4 to 2.5 billion years ago, is called the “Archaean era”. Vegetable and animal world It was 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, and there were no mountainous landscapes or depressions at all. This is the period when mineral deposits began to form: graphite, nickel, sulfur, iron and gold.
Rays of sunlight could not yet penetrate through the mixed hydrosphere and atmosphere, which made up a single shell of steam and gas. The resulting greenhouse effect prevented the sun from touching the earth.
The Archean era was named so by the American scientist J. Dana in 1872. The term “archaean” from ancient Greek means “ancient.” The Archean is divided into four main eras, starting from the most ancient - the Eoarchean - and ending with the Neoarchean. Let's look at them in more detail.
The beginning of the Archean - Eoarchean
The 400 million year period began about 4 billion years ago. The Eoarchean is characterized by frequent meteorite falls 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 the laying of the most ancient 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 World Ocean 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 Earth's air envelope reached 120 °C.
The first organisms of the Archean era began to appear precisely 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 considered to be the beginning of the formation of the first earthly continent - Vaalbara.
Second era - Paleoarchean
The Archean era of this period covers a time period 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 ending, and the still shallow World Ocean appeared. The Earth's core became more solid, which strengthened the Earth's magnetic field almost to modern levels.
It is this period that allows us to assert that already in those times 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 the conditions for the development of new forms of life.
Mesoarchean: Vaalbara Schism
Mesoarchean - a period that lasted 0.4 billion years (began 3.2 billion years ago). It was then that Vaalbara split, which split at an angle of 30° into two separate parts. The most famous crater in our times in Greenland also appeared from a collision with an asteroid. Perhaps the first glaciation, the Pongolian glaciation, occurred on Earth during the Mesoarchean period.
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 is Neoarchean
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 large amounts 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 most ancient deposits of minerals, which are still widely used today. This was also 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 claim that the origin of life began precisely during 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 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 shells of modern mollusks and is found in the exoskeleton of corals.
Cyanobacteria became the culprits in the formation of deposits of not only carbonate, but also siliceous sedimentary formations.
The Archean era is characterized by the appearance of the first prokaryotes - prenuclear single-celled organisms.
Characteristics of prokaryotes
Living organisms do not have a formed nucleus, but they are a full-fledged cell. By feeding through photosynthesis, prokaryotes produce oxygen. The DNA information (nucleotide) carried by the cell 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. At the same time, their structure of life organization differs from that of other types of microbes. By appearance Archaea are similar to bacteria, but some have an unusual flat or square shape.
There are five types of archaea, although it is quite difficult to classify them. Grow archaebacteria in nutrient media impossible, so all research is 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 to humans and can survive in the most extreme conditions: ocean, hot springs, soil, salt lakes. The most abundant species of archaea makes up a significant portion of the plankton in the oceans, which serves as food for marine animals.
Some species even live in the human intestines, helping to carry out digestive processes. Archaea are used to create biological gas, clean sewers, and settlers.
Plants
As you can understand, the Archean era, whose flora was slightly richer than animals, was 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 established that the only plants at that time were filamentous algae, in which, by the way, bacteria lived.
And blue-green algae, previously mistakenly considered plants, turned out to be colonies of cyanobacteria that use both carbon and oxygen as a resource to support life and are not part of flora archaea.
filamentous algae
The Archean era was marked by the appearance of the first plants. These are single-celled filamentous algae that are the simplest form of flora. They do not have a specific shape, structure, organs or 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 can have branches. They can easily either float freely or attach to different surface. Reproduction occurs by dividing the threads into two separate ones. Both all threads and only the outermost, or main, threads can be capable of division.
Algae do not have flagella; they are connected to each other through microscopic cytoplasmic bridges (plasmodesmata).
During evolution, algae formed another form of life - lichens.
The Archaean Era is the first period when biological life on Earth appeared from almost 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 World Ocean, the atmosphere, suitable for life of other more complex forms of flora and fauna.
The end of the Archean 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 characteristics of waterfowl and settled in the ocean.
Archaea or Archean eon- one of the four main periods in the history of the Earth, lasted from 4.0 to 2.5 billion years ago. At this time, there was no oxygen atmosphere on Earth, but the first anaerobic bacteria appeared, which formed many of the existing deposits of minerals: sulfur, graphite, iron and nickel.
Eoarchaean
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. The active formation of the hydrosphere begins, and salty bodies of hot water appear, isolated from each other. Carbon dioxide predominates in the atmosphere; air temperatures reach 120 °C. The first living organisms appear - cyanobacteria, which begin to produce oxygen through photosynthesis. The formation of a hypothetical Vaalbara, the main earthly continent, is taking place.
Paleoarchaean
The next period of the Archean era covers a period of time of 400 million years. The Earth's magnetic field is strengthened by increasing the hardness of the earth's core. This has a beneficial effect on the living conditions and development of simple microorganisms. A day lasts about 15 hours. The formation of the world's oceans takes place. Changes in underwater 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 earth's 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 splits into two parts. As a result of a sharp cooling of the planet, which is caused by constant volcanic processes, the Pongol glacial formation is formed. During this period, the number of cyanobacteria begins to actively grow. Chemolithotrophic organisms develop that do not require oxygen and sunlight. Vaalbar is fully formed. Its size is approximately equal to the size of modern Madagascar. The formation of the continent of Ur begins. Large islands slowly begin to form from volcanoes. The atmosphere, as before, is dominated by carbon dioxide. The air temperature remains high.
Neoarchaean
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, and the level of oxygen in the atmosphere increases. The continent of Ur becomes the basis of Kenorland. Most of the planet is occupied by volcanoes. Their active activity leads to increased formation of minerals. Gold, silver, granites, diorites and other equally important natural resources were formed during the Neoarchean period. In the last centuries of the Archean era, the first multicellular organisms appeared, which were later divided into terrestrial and marine inhabitants. Bacteria begin to develop the sexual process of reproduction. Haploid microorganisms have one set of chromosomes. They constantly adapt to changes in their environment, but at the same time they do not develop 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 Archaea
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 to the surface of something. In the future, the algae will form a new form of life - lichens.
During the Archean era, the first prokaryotes appeared - single-celled organisms without a nucleus. Through photosynthesis, prokaryotes produce oxygen and create favorable conditions for the emergence of new life forms. Prokaryotes are divided into two domains - bacteria and archaea.
It has now been established that archaea have features that distinguish them from other living organisms. Therefore, the classification that combines them with bacteria into one group is considered outdated. Externally, 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 digestive processes. Other types are used to clean sewage ditches and ditches.
There is a theory, unconfirmed by facts, that during the Archean era the birth and development of eukaryotes - microorganisms of the fungal kingdom, similar to yeasts - 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 find out anything about the climate zones of this period. The existence of zones of different climates in the Archean era can be judged by ancient glacial deposits - tillites. Remains of glaciations have been found in America, Africa, and Siberia today. It is not yet possible to determine their true size. Most likely, glacial deposits covered only mountain peaks, because vast continents had not yet been formed during the Archean era. 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 Archean
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 atmospheric temperature reaches 120 degrees. If nitrogen predominated 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 noticeably. The temperature of water and air also dropped. And the amount of oxygen increased. Thus, the planet gradually became suitable for life of various organisms.
Archean minerals
It was during the Archean era that the greatest formation of minerals occurred. 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 down by this era of the earth's life. On the territory of the Russian Federation, Archean deposits have been found in the Urals and Siberia.
The oldest period of the earth's existence, covering the time period 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 among the water bodies on the planet there was only one shallow ocean, consisting of several reservoirs with saturated salt water, and there were no mountainous landscapes or depressions at all. This is the period when mineral deposits began to form: graphite, nickel, sulfur, iron and gold.
Rays of sunlight could not yet penetrate through the mixed hydrosphere and atmosphere, which made up a single shell of steam and gas. The resulting greenhouse effect prevented the sun from touching the earth.
The Archean era was named so by the American scientist J. Dana in 1872. The term “archaean” from ancient Greek means “ancient.” The Archean is divided into four main eras, starting from the most ancient - the Eoarchean - and ending with the Neoarchean. Let's look at them in more detail.
The beginning of the Archean - Eoarchean
The 400 million year period began about 4 billion years ago. The Eoarchean is characterized by frequent meteorite falls 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 the laying of the most ancient 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 World Ocean 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 Earth's air envelope reached 120 °C.
The first organisms of the Archean era began to appear precisely 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 considered to be the beginning of the formation of the first earthly continent - Vaalbara.
Second era - Paleoarchean
The Archean era of this period covers a time period 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 ending, and the still shallow World Ocean appeared. The Earth's core became more solid, which strengthened the Earth's magnetic field almost to modern levels.
It is this period that allows us to assert that already in those times 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 the conditions for the development of new forms of life.
Mesoarchean: Vaalbara Schism
Mesoarchean - a period that lasted 0.4 billion years (began 3.2 billion years ago). It was then that Vaalbara split, which split at an angle of 30° into two separate parts. The most famous crater in our times in Greenland also appeared from a collision with an asteroid. Perhaps the first glaciation, the Pongolian glaciation, occurred on Earth during the Mesoarchean period.
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 is Neoarchean
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 large amounts 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 most ancient deposits of minerals, which are still widely used today. This was also 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 claim that the origin of life began precisely during 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 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 shells of modern mollusks and is found in the exoskeleton of corals.
Cyanobacteria became the culprits in the formation of deposits of not only carbonate, but also siliceous sedimentary formations.
The Archean era is characterized by the appearance of the first prokaryotes - prenuclear single-celled organisms.
Characteristics of prokaryotes
Living organisms do not have a formed nucleus, but they are a full-fledged cell. By feeding through photosynthesis, prokaryotes produce oxygen. The DNA information (nucleotide) carried by the cell 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. At the same time, their structure of life organization differs from that of other types of microbes. Archaea are similar in appearance to bacteria, but some have an unusual flat or square shape.
There are five types of archaea, although it is quite difficult to classify them. It is impossible to grow archaebacteria in nutrient media, so all research is 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 to humans and can survive in the most extreme conditions: ocean, hot springs, soil, salt lakes. The most abundant species of archaea makes up a significant portion of the plankton in the oceans, which serves as food for marine animals.
Some species even live in the human intestines, helping to carry out digestive processes. Archaea are used to create biological gas, clean sewers, and settlers.
Plants
As you can understand, the Archean era, whose flora was slightly richer than animals, was 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 established that the only plants at that time were filamentous algae, in which, by the way, bacteria lived.
And blue-green algae, previously mistakenly considered plants, turned out to be colonies of cyanobacteria that use both carbon and oxygen as a resource to support life and are not part of the archaeal plant world.
filamentous algae
The Archean era was marked by the appearance of the first plants. These are single-celled filamentous algae that are the simplest form of flora. They do not have a specific shape, structure, organs or 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 can have branches. They can easily either float freely or attach to various surfaces. Reproduction occurs by dividing the threads into two separate ones. Both all threads and only the outermost, or main, threads can be capable of division.
Algae do not have flagella; they are connected to each other through microscopic cytoplasmic bridges (plasmodesmata).
During evolution, algae formed another form of life - lichens.
The Archaean Era is the first period when biological life on Earth appeared from almost 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 World Ocean, the atmosphere, suitable for life of other more complex forms of flora and fauna.
The end of the Archean 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 characteristics of waterfowl and settled in the ocean.