Periods of geological history of the Earth in chronological order. The emergence of life
Geochronology is a conditional division of the whole historyEarth for long periods of time, which are characterized by some specific feature. Periods of geological history of the Earth in chronological order were adopted at the first international congresses of geologists. The established separation of periods is used in geology, geography and related sciences.
Period subdivisions
There are two scales that determine the periodsthe existence of our planet. They are called: stratigraphic, studying sections of fossil deposits, and geochronological, taking into account the change in the organic and inorganic world.
The largest periods
Stratigraphically, the geological periods of the geological history of the Earth in chronological order are divided into three large time intervals, which scientists call eonotems:
- archaean;
- Proterozoic;
- Phanerozoic.
This division has different timeframework. The first period of life lasted more than 2 billion years, and the last one lasts about 512 million years. Geological eras and the history of life on Earth are inextricably linked. Gradual quantitative changes in the percentage content of oxygen, water, stabilization of atmospheric pressure and temperature cause a qualitative leap in the evolutionary process. Observe this relationship can be an example of a brief description of the three main periods of life of the Earth.
Archaean
Archean and Proterozoic times are 4/5 of the entire history of the existence of our planet. From the Archean period begins the history of the Earth. Geological time scale postpones the beginning of the Archaean period by 4a billion years ago. The Archean era - the oldest, the longest in time - lasts about 12 million years. It is at this time that our planet cools, a metal core is formed, the first magmatic rocks such as diorite and granite are formed. Traces of ancient times, scientists found on the edge of the Greenland Shield. In the middle of the Archean period, the first continent is being formed, which the scientists called Valbaru.
At the same time on Earth the first livingorganisms. Most likely, they were extinct anaerobic bacteria. The emergence of life is directly related to the processes of photosynthesis, which immediately divides all living organisms into plants and animals. The first photosynthesis took place in blue-green algae and in cyanobacteria, which had a primitive internal structure such that they did not even have nuclei.
Proterozoic
The very first period in the history of the Proterozoiccharacterized by a sharp decrease in the level of oxygen in the atmosphere. Perhaps this happened at the time of some unexplored cosmic catastrophe, but even this change proved to be fatal to anaerobic microorganisms - for them molecular oxygen turned out to be fatal. Thus, the first living organisms on Earth became extinct, giving the opportunity to exist other forms of life aimed at consuming O2.
In the atmosphere, the level of carbon dioxide decreases andthe amount of water increases - the first World Ocean is formed, which, of course, was much smaller than today's. And the continents merge into a new continent, which was named Rodinia - this event took place 1150 million years ago. At the end of this period, the first ice age begins, connected with the displacement of the magnetic poles and, possibly, the change in the period of rotation of our planet. By this time, scientists attribute the earliest finds of the remains of the first living organisms - this is due to the emergence of skeletons in living beings.
Phanerozoic
The closest to us periods of geological historyThe Earth in chronological order is called the Phanerozoic. The most obvious characteristic of this time interval is the emergence of life in the modern sense of the word. The Phanerozoic era began 542 million years ago and continues to this day. A sharp increase in oxygen has provoked a real boom in the emergence of new amazing plants and animals. Scientists call this process Cambrian explosion. In the Phanerozoic, most species of modern plants have appeared, and animals have acquired a spine and made up a new class of living beings on Earth.
This division gives a general idea of how,as scientists call periods of geological history of the Earth. In chronological order, they are very easy to remember - the first letters of the Archaean, Proterozoic and Phanerozoic eras are arranged in alphabetical order.
