Geochronology is a conditional division of the entire history of the Earth into long periods of time, which are characterized by any particular sign. The periods of the 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.
Subdivisions of periods
There are two scales that determine the periods of existence of our planet. They are called: stratigraphic, studying sections of fossil deposits, and geochronological, taking into account changes in the organic and inorganic world.
In large periods of
time, the geological periods of the Earth’s development bear certain names: eons, epochs, periods, centuries, times. There are smaller time intervals that are mentioned in scientific papers, but they do not play a role for a general understanding of the history of the Earth.
The largest periods
Stratigraphically, the geological periods of the Earth’s geological history are chronologically divided into three large time intervals, which scientists call eonotems:
- Archean;
- Proterozoic;
- Phanerozoic.
This separation has a different time frame. The first period of life lasted more than 2 billion years, and the last lasts about 512 million years. Geological eras and the history of life on Earth are inextricably linked. Gradual quantitative changes in the percentage of oxygen, water, stabilization of atmospheric pressure and temperature cause a qualitative leap in the evolutionary process. This relationship can be observed by the example of a brief description of the three main periods of the Earth’s life.
Archaea
Archean and Proterozoic time is 4/5 of the entire history of our planet. From the Archean period begins the history of the Earth. The geological timeline pushes the beginning of the Archean period 4 billion years ago. The Archean era - the oldest, longest in time - lasts about 12 million years. It was at this time that our planet cools down, a metal core forms, the first igneous rocks, such as diorite and granite, form. Traces of ancient times, scientists found on the edge of the Greenland shield. In the middle of the Archean period, the first continent was formed, which scientists called Valbar.
At the same time, the first living organisms were born on Earth. 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 occurred in blue-green algae and in cyanobacteria, which had such a primitive internal structure that even nuclei were absent in them.
Proterozoic
The very first period in the history of the Proterozoic is characterized 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 such a change was fatal for anaerobic microorganisms - for them, molecular oxygen was fatal. So, the first living organisms on Earth died out, giving the opportunity to exist other forms of life, aimed at the consumption of O 2 .
In the atmosphere, the level of carbon dioxide decreases and the amount of water increases - the first World Ocean is formed, which, of course, was much smaller than today. And the continents are merging into a new continent, which was named Rodinia - this event occurred 1150 million years ago. At the end of this period, the first ice age begins, associated with the displacement of the magnetic poles and, possibly, a change in the rotation period of our planet. By this time, scientists attribute the oldest finds to the remains of the first living organisms - this is due to the appearance of skeletons in living beings.
Phanerozoic
The periods of the geological history of the Earth that are closest to us in chronological order are 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 provoked a real boom in the emergence of new amazing plants and animals. Scientists call this process the Cambrian explosion. Most species of modern plants appeared in Phanerozoic, and animals found their spine and made up a new class of living creatures on Earth.
This division gives a general idea of what scientists call the periods of the geological history of the Earth. In chronological order they are very easy to remember - the first letters of the Archean, Proterozoic and Phanerozoic era are arranged in alphabetical order.