What periods were the longest on earth. Geological eras

I have long been interested in the history of our planet. After all, the world that we see today was not always so. It is difficult to even imagine what was on our planet many millions or even several billion years ago. Each period was characterized by some of its own characteristics.

What were the main eras and periods on our planet

I will touch a little on the topic of eras and periods in in general terms. So, all 4.5 billion years, scientists divide like this.

• The Precambrian era (Catarchean, Archean and Proterozoic periods) - in terms of duration, this is the longest era, which lasted almost 4 billion years.
• The Paleozoic era (includes six periods) - lasted a little less than 290 million years, at which time the conditions for life were finally formed, first in water, and then on land.
• The Mesozoic era (includes three periods) is the era of the dominance of reptiles on our planet.
• The Cenozoic era (consists of the Paleogene, Neogene and Anthropogenic periods) - in this era we now live, and to be more specific, in the Anthropogene.

Each era usually ended with some kind of cataclysm.

Mesozoic era

Almost everyone knows about this era, because many have seen american film"Jurassic Park", which featured different breeds dinosaurs. Yes, yes, it was these animals that dominated at that time.

The Mesozoic consists of the following segments:

• Triassic;
• Jurassic;
• chalky.

During the Jurassic period, dinosaurs reached greatest development. There were giant species that reached a length of up to thirty meters. There were also very large and tall trees, and there was a minimum of vegetation on the ground. Of the low-growing plants, ferns predominated.

At the beginning of this era, there was a single mainland, but then it split into six parts, which eventually took on a modern look.

Two million years before the extinction of the dinosaurs, the most formidable predator appeared - Tyrannosaurus. And these reptiles died out after the earth collided with a comet. As a result, about 65% of all life on the planet died.

This era ended about sixty-five million years ago.

Geological time and methods for its determination

In the study of the Earth as a unique cosmic object, the idea of ​​its evolution occupies a central place, therefore an important quantitative evolutionary parameter is geological time. The study of this time is engaged in a special science called Geochronology- geological reckoning. Geochronology May be absolute and relative.

Remark 1

Absolute geochronology deals with the determination of the absolute age of rocks, which is expressed in units of time and, as a rule, in millions of years.

The determination of this age is based on the rate of decay of isotopes of radioactive elements. This speed is a constant value and does not depend on the intensity of physical and chemical processes. Age determination is based on nuclear physics methods. Minerals containing radioactive elements, when formed crystal lattices, form closed system. In this system, the accumulation of radioactive decay products occurs. As a result, the age of the mineral can be determined if the rate of this process is known. The half-life of radium, for example, is $1590$ years, and the complete decay of the element will occur in $10$ times the half-life. Nuclear geochronology has its leading methods − lead, potassium-argon, rubidium-strontium and radiocarbon.

Methods of nuclear geochronology made it possible to determine the age of the planet, as well as the duration of eras and periods. Radiological time measurement proposed P. Curie and E. Rutherford at the beginning of the $XX$ century.

Relative geochronology operates with such concepts as " early age, middle, late. There are several developed methods for determining the relative age of rocks. They fall into two groups - paleontological and non-paleontological.

First play a major role due to their versatility and ubiquity. The exception is the absence of organic remains in the rocks. With the help of paleontological methods, the remains of ancient extinct organisms are studied. Each rock layer has its own complex of organic remains. In each young layer there will be more remains of highly organized plants and animals. The higher the layer lies, the younger it is. A similar pattern was established by the Englishman W. Smith. He owns the first geological map of England, on which the rocks were divided by age.

Non-paleontological methods determinations of the relative age of rocks are used in cases where there are no organic remains in them. More efficient then will be stratigraphic, lithological, tectonic, geophysical methods. Using the stratigraphic method, it is possible to determine the sequence of stratification of layers in their normal occurrence, i.e. the underlying layers will be older.

Remark 3

The sequence of formation of rocks determines relative geochronology, and their age in units of time determines already absolute geochronology. Task geological time is to determine the chronological sequence of geological events.

Geological table

To determine the age of rocks and their study, scientists use various methods, and for this purpose a special scale has been compiled. Geological time on this scale is divided into time periods, each of which corresponds to a certain stage in the formation of the earth's crust and the development of living organisms. The scale is called geochronological table, which includes the following divisions: eon, era, period, epoch, century, time. Each geochronological unit is characterized by its own set of deposits, which is called stratigraphic: eonoteme, group, system, department, tier, zone. A group, for example, is a stratigraphic unit, and the corresponding temporal geochronological unit is era. Based on this, there are two scales - stratigraphic and geochronological. The first scale is used when it comes to deposits, because in any period of time some geological events took place on the Earth. The second scale is needed to determine relative time. Since the adoption of the scale, the content of the scale has been changed and refined.

The largest stratigraphic units at present are eonotemes - Archean, Proterozoic, Phanerozoic. In the geochronological scale, they correspond to zones of different duration. According to the time of existence on Earth, they are distinguished Archean and Proterozoic eonotemes covering nearly $80$% of the time. Phanerozoic eon in time is much less than the previous eon and covers only $ 570 $ million years. This ionoteme is divided into three main groups - Paleozoic, Mesozoic, Cenozoic.

The names of eonotems and groups are of Greek origin:

• Archeos means ancient;
• Proteros - primary;
• Paleos - ancient;
• Mezos - medium;
• Cainos is new.

From the word " zoiko s”, which means vital, the word “ zoi". Based on this, the eras of life on the planet are distinguished, for example, the Mesozoic era means the era of average life.

Eras and periods

According to the geochronological table, the history of the Earth is divided into five geological eras: Archean, Proterozoic, Paleozoic, Mesozoic, Cenozoic. The eras are further subdivided into periods. There are much more of them - $12$. The duration of the periods varies from $20$-$100$ million years. The last one points to its incompleteness. Quaternary period of the Cenozoic era, its duration is only $1.8 million years.

Archean era. This time began after the formation of the earth's crust on the planet. By this time there were mountains on the Earth and the processes of erosion and sedimentation had come into play. The Archean lasted for approximately $2 billion years. This era is the longest in duration, during which volcanic activity was widespread on Earth, there were deep uplifts, which resulted in the formation of mountains. Most of the fossils were destroyed under the influence of high temperature, pressure, mass movement, but little data about that time was preserved. In the rocks of the Archean era, pure carbon is found in dispersed form. Scientists believe that these are altered remains of animals and plants. If the amount of graphite reflects the amount of living matter, then there was a lot of it in the Archaean.

Proterozoic era. In terms of duration, this is the second era, spanning $1 billion years. During the era, there was the deposition of a large amount of precipitation and one significant glaciation. Ice sheets extended from the equator to $20$ degrees of latitude. Fossils found in the rocks of this time are evidence of the existence of life and its evolutionary development. Spicules of sponges, remains of jellyfish, fungi, algae, arthropods, etc. have been found in the Proterozoic deposits.

Palaeozoic. This era stands out six periods:

• Cambrian;
• Ordovician,
• Silur;
• Devonian;
• Carbon or coal;
• Perm or Perm.

The duration of the Paleozoic is $370$ million years. During this time, representatives of all types and classes of animals appeared. Only birds and mammals were missing.

Mesozoic era. The era is divided into three period:

• Triassic;

The era started about $230 million years ago and lasted $167 million years. During the first two periods Triassic and Jurassic- most of the continental regions rose above sea level. The climate of the Triassic is dry and warm, and in the Jurassic it became even warmer, but was already humid. In state Arizona there is a famous stone forest that has existed since Triassic period. True, only trunks, logs and stumps remained from the once mighty trees. At the end of the Mesozoic era, or rather in the Cretaceous period, a gradual advance of the sea takes place on the continents. The North American continent experienced a subsidence at the end of the Cretaceous, and as a result, the waters of the Gulf of Mexico joined with the waters of the Arctic basin. The mainland was divided into two parts. The end of the Cretaceous period is characterized by a large uplift, called Alpine orogeny. At this time there were Rocky Mountains, Alps, Himalayas, Andes. In the West North America intense volcanic activity began.

Cenozoic era. This new era, which has not yet ended and continues at the present time.

The era was divided into three periods:

• Paleogene;
• Neogene;
• Quaternary.

Quaternary period has whole line unique features. This is the time of the final formation of the modern face of the Earth and ice ages. Became independent New Guinea and Australia, moving closer to Asia. Antarctica has remained in its place. Two Americas united. Of the three periods of the era, the most interesting is quaternary period or anthropogenic. It continues today, and was allocated in $1829$ by a Belgian geologist J. Denoyer. Coolings are replaced by warmings, but its most important feature is appearance of man.

Modern man lives in the Quaternary period of the Cenozoic era.

Life on Earth originated over 3.5 billion years ago, immediately after the completion of the formation of the earth's crust. Throughout time, the emergence and development of living organisms influenced the formation of relief and climate. Also, tectonic and climatic changes that have taken place over the years have influenced the development of life on Earth.

A table of the development of life on Earth can be compiled based on the chronology of events. The entire history of the Earth can be divided into certain stages. The largest of them are the eras of life. They are divided into eras, eras - into periods, periods -for epochs, epochs - for centuries.

Ages of life on earth

The entire period of the existence of life on Earth can be divided into 2 periods: the Precambrian, or Cryptozoic (primary period, 3.6 to 0.6 billion years), and Phanerozoic.

Cryptozoic includes the Archean (ancient life) and Proterozoic (primary life) eras.

Phanerozoic includes Paleozoic (ancient life), Mesozoic (middle life) and Cenozoic ( new life) era.

These 2 periods of life development are usually divided into smaller ones - eras. The boundaries between eras are global evolutionary events, extinctions. In turn, eras are divided into periods, periods - into epochs. The history of the development of life on Earth is directly related to changes in the earth's crust and the planet's climate.

Era of development, countdown

It is customary to single out the most significant events in special time intervals - eras. Time is counted backwards, from ancient life to the new. There are 5 eras:

Periods of development of life on Earth

The Paleozoic, Mesozoic and Cenozoic eras include periods of development. These are smaller periods of time, compared to eras.

• Cambrian (Cambrian).
• Ordovician.
• Silurian (Silur).
• Devonian (Devonian).
• Carboniferous (carbon).
• Perm (Perm).

• Lower Tertiary (Paleogene).
• Upper Tertiary (Neogene).
• Quaternary, or anthropogen (human development).

The first 2 periods are included in the Tertiary period lasting 59 million years.

Proterozoic era (early life)

6. Perm (Perm)

2. Upper Tertiary (Neogene)

3. Quaternary or anthropogen (human development)

The development of living organisms

The table of the development of life on Earth involves the division not only into time intervals, but also into certain stages of the formation of living organisms, possible climatic changes (ice age, global warming).

• Archean era. The most significant changes in the evolution of living organisms are the appearance of blue-green algae - prokaryotes capable of reproduction and photosynthesis, the emergence of multicellular organisms. The appearance of living protein substances (heterotrophs) capable of absorbing organic substances dissolved in water. In the future, the appearance of these living organisms made it possible to divide the world into flora and fauna.

• Mesozoic era.

• Triassic. Distribution of plants (gymnosperms). An increase in the number of reptiles. The first mammals, bony fish.
• Jurassic period. The predominance of gymnosperms, the emergence of angiosperms. The appearance of the first bird, the flowering of cephalopods.
• Cretaceous period. Spread of angiosperms, reduction of other plant species. The development of bony fish, mammals and birds.

• Cenozoic era.
  • Lower Tertiary period (Paleogene). The flowering of angiosperms. The development of insects and mammals, the appearance of lemurs, later primates.
  • Upper Tertiary period (Neogene). Formation modern plants. The appearance of human ancestors.
  • Quaternary period (anthropogen). Formation of modern plants, animals. The appearance of man.

Development of conditions of inanimate nature, climate change

The table of the development of life on Earth cannot be presented without data on changes in inanimate nature. The emergence and development of life on Earth, new species of plants and animals, all this is accompanied by changes in inanimate nature and climate.

Climate Change: Archean Era

The history of the development of life on Earth began through the stage of the predominance of land over water resources. The relief was poorly outlined. The atmosphere is dominated by carbon dioxide, the amount of oxygen is minimal. Salinity is low in shallow water.

The Archean era is characterized by volcanic eruptions, lightning, black clouds. The rocks are rich in graphite.

Climatic changes during the Proterozoic era

Land is a stone desert, all living organisms live in water. Oxygen accumulates in the atmosphere.

Climate change: the Paleozoic era

During various periods of the Paleozoic era, the following climate changes occurred:

• Cambrian period. The land is still deserted. The climate is hot.
• Ordovician period. The most significant changes are the flooding of almost all northern platforms.
• Silurian. Tectonic changes, the conditions of inanimate nature are diverse. Mountain building occurs, the seas prevail over the land. Regions of different climates, including areas of cooling, were determined.
• Devonian. Dry climate prevails, continental. Formation of intermountain depressions.
• Carboniferous period. The sinking of the continents, wetlands. The climate is warm and humid, with a lot of oxygen and carbon dioxide in the atmosphere.
• Permian period. Hot climate, volcanic activity, mountain building, drying up of swamps.

During the Paleozoic era, the mountains of the Caledonian folding formed. Such changes in the relief affected the world's oceans - the sea basins were reduced, a significant land area was formed.

The Paleozoic era marked the beginning of almost all major deposits of oil and coal.

Climatic changes in the Mesozoic

The climate of different periods of the Mesozoic is characterized by the following features:

• Triassic. Volcanic activity, the climate is sharply continental, warm.
• Jurassic period. Mild and warm climate. The seas prevail over the land.
• Cretaceous period. Retreat of the seas from the land. The climate is warm, but at the end of the period, global warming is replaced by cooling.

In the Mesozoic era, the previously formed mountain systems are destroyed, the plains go under water ( Western Siberia). In the second half of the era, the Cordilleras, the mountains of Eastern Siberia, Indochina, partly Tibet, formed the mountains of the Mesozoic folding. A hot and humid climate prevails, contributing to the formation of swamps and peat bogs.

Climate change - Cenozoic era

In the Cenozoic era, there was a general uplift of the Earth's surface. The climate has changed. Numerous glaciations of the earth covers advancing from the north have changed the appearance of the continents of the Northern Hemisphere. Due to such changes, hilly plains were formed.

• Lower Tertiary period. Mild climate. Division into 3 climatic zones. Formation of continents.
• Upper Tertiary period. Dry climate. The emergence of steppes, savannahs.
• Quaternary period. Multiple glaciation of the northern hemisphere. Climate cooling.

All changes during the development of life on Earth can be written in the form of a table that will reflect the most significant stages in the formation and development modern world. Despite the already known methods of research, and now scientists continue to study history, make new discoveries that allow modern society learn how life developed on Earth before the appearance of man.

Development of life on Earth lasts over 3 billion years. And this process is still going on.

Bacteria were the first living things in the Archaean. Then unicellular algae, animals and fungi appeared. The unicellular ones have been replaced by multicellular ones. At the beginning of the Paleozoic, life was already very diverse: representatives of all types of invertebrates lived in the seas, and the first land plants appeared on land. In the following eras, over many millions of years, they formed and died out different groups plants and animals. Gradually, the living world became more and more similar to the modern one.

2.6. History of the development of life

Previously, scientists believed that living things came from living things. Bacterial spores were brought from space. Some bacteria have created organic matter others consumed and destroyed them. As a result, an ancient ecosystem arose, the components of which were connected by the circulation of substances.

Modern scientists have proved that living things originated from inanimate nature. IN aquatic environment organic substances were formed from inorganic substances under the influence of the energy of the Sun and the internal energy of the Earth. They formed the oldest organisms - bacteria.

There are several eras in the history of the development of life on Earth.

archaeus

The first organisms were prokaryotes. In the Archean era, a biosphere already existed, consisting mainly of prokaryotes. The very first living creatures on the planet are bacteria. Some of them were capable of photosynthesis. Photosynthesis was carried out by cyanobacteria (blue-green).

Proterozoic

As the oxygen content of the atmosphere increased, eukaryotic organisms began to appear. In the Proterozoic, unicellular plants arose in the aquatic environment, and then unicellular animals and fungi. important event Proterozoic was the emergence of multicellular organisms. By the end of the Proterozoic, various types of invertebrates and chordates had already appeared.

Paleozoic

Plants

Gradually, dry land appeared in place of warm shallow seas. As a result, the first land plants originated from multicellular green algae. Forests arose in the second half of the Paleozoic. They consisted of ancient ferns, horsetails and club mosses that reproduced by spores.

Animals

At the beginning of the Paleozoic, marine invertebrates flourished. Vertebrate animals - armored fish - developed and spread in the seas.

In the Paleozoic, the first terrestrial vertebrates appeared - the oldest amphibians. From them at the end of the era came the first reptiles.

The most numerous in the seas of the Paleozoic (era ancient life) were trilobites - fossil arthropods, outwardly similar to giant wood lice. Trilobites - existed at the beginning of the Paleozoic, completely died out 200 million years ago. They swam and crawled in shallow bays, feeding on plants and animal remains. There is an assumption that there were predators among the trilobites.

The very first among animals to master the land were arachnids and giant flying insects - the ancestors of modern dragonflies. Their wingspan reached 1.5 m.

Mesozoic

In the Mesozoic, the climate became more arid. The ancient forests gradually disappeared. The spore-bearing plants were replaced by seeds. Among animals, reptiles flourished, including dinosaurs. At the end of the Mesozoic, many types of ancient seed plants and dinosaurs became extinct.

Animals

The largest of the dinosaurs were the brachiosaurs. They reached more than 30 m in length and weighed 50 tons. These dinosaurs had a huge body, long tail and neck, and a small head. If they lived in our time, they would be taller than five-story houses.

Plants

The most complexly organized plants are flowering plants. They appeared in the middle of the Mesozoic (the era of middle life). Material from the site http://wikiwhat.ru

Cenozoic

Cenozoic - the heyday of birds, mammals, insects and flowering plants. Warm-bloodedness arose in birds and mammals due to the more perfect structure of organ systems. They became less dependent on environmental conditions and spread widely on Earth.

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 production of minerals. Gold, silver, granites, diorites and other equally important natural resources, were formed during the Neoarchean period. IN 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 to free swimming or stick to the surface of something. In the future, algae will form new form life - lichens.

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

Archaea

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

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

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 about climatic zones of this period. The existence of zones of different climates in the Archean era can be judged by the ancient glacial deposits- tillites. The remains of glaciations are now found in America, Africa, and Siberia. Their true dimensions is not yet possible to determine. 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 early period there was little water on the ground. The water temperature during the Archean era reached 90°C. This indicates the saturation of the atmosphere with carbon dioxide. There was very little nitrogen in it, there was almost no oxygen in the early stages, the remaining gases are quickly destroyed under the influence of sunlight. The temperature of the atmosphere reaches 120 degrees. If nitrogen prevailed in the atmosphere, then the temperature would not be lower than 140 degrees.

IN late period, after the formation of the oceans, 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. In the territory 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 history of the planet Earth already has about 7 billion years. During this time, our common home has undergone significant changes, which was the result of changing periods. V chronological order reveal the entire history of the planet from its very appearance to the present day.

Geological chronology

The history of the Earth, presented in the form of eons, groups, periods and epochs, is a certain grouped chronology. At the first international congresses of geology, a special chronological scale was developed, which represented the periodization of the Earth. Subsequently, this scale was replenished new information and changed, as a result, now it reflects all geological periods in chronological order.

The largest subdivisions in this scale are eonotemes, eras and periods.

Formation of the Earth

The geological periods of the Earth in chronological order begin their history precisely with the formation of the planet. Scientists have come to the conclusion that the Earth was formed about 4.5 billion years ago. The very process of its formation was very long and, possibly, began as early as 7 billion years ago from small cosmic particles. Over time, the gravitational force grew, along with it, the speed of bodies falling on the forming planet increased. Kinetic energy was transformed into heat, resulting in a gradual heating of the Earth.

The core of the Earth, according to scientists, was formed over several hundred million years, after which the gradual cooling of the planet began. Currently, the molten core contains 30% of the mass of the Earth. The development of other shells of the planet, according to scientists, has not yet been completed.

Precambrian eon

In the geochronology of the Earth, the first eon is called the Precambrian. It covers the time 4.5 billion - 600 million years ago. That is, the lion's share of the history of the planet is covered by the first. However, this eon is divided into three more - Katarchean, Archean, Proterozoic. And often the first of them stands out in an independent eon.

At this time, the formation of land and water occurred. All this happened during active volcanic activity for almost the entire eon. Shields of all continents were formed in the Precambrian, but traces of life are very rare.

Catharhean eon

The beginning of the history of the Earth - half a billion years of its existence in science is called katarchey. The upper limit of this eon is at around 4 billion years ago.

Popular literature portrays the Catarchean as a time of active volcanic and geothermal changes on the Earth's surface. However, this is not actually true.

The Katharhean eon is a time when volcanic activity was not manifested, and the surface of the Earth was a cold, inhospitable desert. Although quite often there were earthquakes that smoothed the landscape. The surface looked like a dark gray primary substance covered with a layer of regolith. The day at that time was only 6 hours.

archean eon

The second main eon out of four in the history of the Earth lasted about 1.5 billion years - 4-2.5 billion years ago. Then the Earth did not yet have an atmosphere, and therefore there was no life yet, but in this eon bacteria appear, due to the lack of oxygen they were anaerobic. As a result of their activities, today we have deposits of natural resources such as iron, graphite, sulfur and nickel. The history of the term "archaea" dates back to 1872, when it was proposed by the famous American scientist J. Dan. The Archean eon, unlike the previous one, is characterized by high volcanic activity and erosion.

Proterozoic eon

If we consider the geological periods in chronological order, the next billion years took the Proterozoic. This period is also characterized by high volcanic activity and sedimentation, and erosion continues over vast areas.

The formation of the so-called. mountains Currently they are small hills on the plains. The rocks of this eon are very rich in mica, non-ferrous metal ores and iron.

It should be noted that the first living creatures appeared in the Proterozoic period - the simplest microorganisms, algae and fungi. And by the end of the eon, worms, marine invertebrates, and mollusks appear.

Phanerozoic eon

All geological periods in chronological order can be divided into two types - explicit and hidden. Phanerozoic refers to explicit. At this time, a large number of living organisms with mineral skeletons appear. The era preceding the Phanerozoic was called hidden because its traces were practically not found due to the absence of mineral skeletons.

The last about 600 million years of the history of our planet are called the Phanerozoic eon. The most significant events of this eon are the Cambrian explosion, which occurred approximately 540 million years ago, and the five largest extinctions in the history of the planet.

Eras of the Precambrian eon

During the Katarchean and Archean, there were no generally recognized eras and periods, so we will skip their consideration.

The Proterozoic consists of three major eras:

Paleoproterozoic- i.e. ancient, including siderium, riasian period, orosirium and staterium. By the end of this era, the concentration of oxygen in the atmosphere reached its present level.

Mesoproterozoic- average. It consists of three periods - potassium, ectasia and stenia. In this era, algae and bacteria reached their greatest prosperity.

Neoproterozoic- new, consisting of tonium, cryogenium and ediacarium. At this time, the formation of the first supercontinent, Rodinia, takes place, but then the plates parted again. The coldest ice age took place during an era called the Mesoproterozoic, during which most of the planet froze over.

Eras of the Phanerozoic eon

This eon consists of three large epochs, which differ sharply from each other:

Paleozoic, or an era of ancient life. It began about 600 million years ago and ended 230 million years ago. The Paleozoic consists of 7 periods:

1. Cambrian (a temperate climate is formed on Earth, the landscape is low-lying, during this period all modern types animals).
2. Ordovician (the climate on the entire planet is quite warm, even in Antarctica, while the land sinks significantly. The first fish appear).
3. Silurian period (the formation of large inland seas takes place, while the lowlands become increasingly arid due to land uplift. The development of fish continues. The Silurian period is marked by the appearance of the first insects).
4. Devon (appearance of the first amphibians and forests).
5. Lower Carboniferous (dominance of ferns, distribution of sharks).
6. Upper and Middle Carboniferous (appearance of the first reptiles).
7. Perm (most of the ancient animals are dying out).

mesozoic, or the time of the reptiles. Geological history consists of three periods:

1. Triassic (seed ferns die out, gymnosperms dominate, the first dinosaurs and mammals appear).
2. Jura (part of Europe and the western part of America is covered with shallow seas, the appearance of the first toothed birds).
3. Chalk (appearance of maple and oak forests, highest development and the extinction of dinosaurs and toothed birds).

cenozoic, or the time of mammals. Consists of two periods:

1. Tertiary. At the beginning of the period, predators and ungulates reach their dawn, the climate is warm. There is a maximum spread of forests, the oldest mammals are dying out. Approximately 25 million years ago, a person appears and in the Pliocene era, a person arises.
2. Quaternary. Pleistocene - large mammals die out, originate human society 4 ice ages occur, many plant species die out. The modern era - the last ice age ends, gradually the climate takes on its present form. The supremacy of man on the whole planet.

The geological history of our planet has a long and contradictory development. In this process, there was a place for several extinctions of living organisms, repeated ice ages, there were periods of high volcanic activity, there were eras of the dominance of different organisms: from bacteria to humans. The history of the Earth began about 7 billion years ago, it was formed about 4.5 billion years ago, and less than a million years ago, man ceased to have competitors in all living nature.