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. Geological periods in 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 with new information and changed, as a result, now it reflects all geological periods in chronological order.
The largest divisions in this scale are eonotemes, eras and periods.
Earth Formation
Geological periods of the Earth in chronological order begin theirhistory since the formation of the planet. Scientists have concluded that the Earth 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 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 as an independent eon.
At this time, the formation of the earth's crust, land and water. 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.
Catarchaean 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 aeon is at4 billion years ago.
Popular literature depicts the Catarchean as a time of active volcanic and geothermal changes on the Earth's surface. However, this is not actually true.
Katarchean eon - the 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.
Archaean eon
The second major 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, 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. mountainsBaikal folding. At present, they are small hills in 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, 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.
Proterozoic, on the other hand, consists of three large 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 the current level.
Mesoproterozoic - medium. It consists of three periods - potassium, ectasia and stenia. In this eraalgae and bacteria have reached their peak.
Neoproterozoic - a new one, consisting of Tonium, Cryogenium and Ediacaran. 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 major epochs that differ sharply from each other:
Paleozoic, or the era of ancient life. It began about 600 million years ago and ended 230 million years ago. The Paleozoic consists of 7 periods:
- Cambrian (a temperate climate is formed on Earth, the landscape is low-lying, during this period all modern types of animals originate).
- Ordovician (the climate on the entire planet is quite warm, even in Antarctica, while the land sinks significantly. The first fish appear).
- Silurian period (large inland seas are forming, while the lowlands are becoming drier due to land uplift. Fish development continues. The Silurian period is marked by the appearance of the first insects).
- Devon (appearance of the first amphibians and forests).
- Lower Carboniferous (dominance of ferns, spread of sharks).
- Upper and Middle Carboniferous (appearance of the first reptiles).
- Perm (most ancient animals are dying out).
Mesozoic, or the time of reptiles. The geological history of the Mesozoic era consists of threeperiods:
- Triassic (seed ferns die out, gymnosperms dominate, first dinosaurs and mammals appear).
- Jura (part of Europe and western America covered by shallow seas, appearance of first toothed birds).
- Chalk (appearance of maple and oak forests, the highest development and extinction of dinosaurs and toothed birds).
Cenozoic, or the time of mammals. Consists of two periods:
- 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, great apes appear, and in the Pliocene era, humans appear.
- Quaternary. Pleistocene - large mammals die out, human society is born, 4 ice ages occur, many plant species die out. The modern era - the last ice age ends, gradually the climate takes on its current form. The supremacy of man on the entire 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, ice ages repeated, periods of high volcanic activity were observed, there were eras of the dominance of various 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.
