Archea

Archean eon , archean ( ancient Greek ἀρχαῖος - ancient) is one of the four eons of the history of the Earth, spanning from 4.0 to 2.5 billion years ago ^[1] .

The most ancient stage of the life of the Earth. It began at the end of the Late Heavy Bombing about 3.8 billion years ago, before the Oxygen Event, about 2.5 billion years ago. Archaea covers the period from the first preserved solid rocks, which already had traces of a developed prokaryotic life in the form of full-fledged bacterial mats , before the appearance of eukaryotes .

The term “archaea” was suggested in 1872 by the American geologist James Dana ^[2] .

Archaea is divided into four eras (from the latest to the earliest):

• Neoarhey ,
• Mesoarcheal ,
• Paleoarchean ,
• Eoarhea .

Earth biota in the Archean eon was a community of anaerobic prokaryotes ^[3] . Geobiological studies of Archean sedimentary rocks indicate that a developed prokaryotic life on Earth existed more than 3.7–3.8 billion years ago ^[4] , but the question of when oxygenic photosynthesis arose still remains without a clear answer. The first fossils, which are believed to have imprinted filamentous photosynthetic organisms, were dated to 3.4 billion years ^{[5] [6]} . In the same period, many existing deposits of sulfur, graphite , iron and nickel are being actively formed.

In the early Archean, the atmosphere and hydrosphere, apparently, represented a mixed gas-vapor mass, which enveloped the entire planet with a powerful and dense layer. Its permeability to the sun was very weak, so darkness reigned on the surface of the Earth. The vapor-gas envelope consisted of water vapor and a certain amount of sour smoke. It was characterized by high chemical activity, as a result of which it actively affected the basaltic surface of the Earth. The mountainous landscape, as well as the deep depressions, were absent on Earth. It is believed that the density and pressure of the atmosphere in the Late Archean were significantly higher than the modern ones, but according to the results of some new studies, their values ​​were inferior to those of more than twice ^[7] . In the epoch of the Archean, the vapor-gas envelope was differentiated into the atmosphere and hydrosphere. The Archean Ocean was shallow, and its waters were a strong and very acidic saline solution ^[8] .

According to a study by Tanai Cardona and his colleagues at Imperial College London, oxygenic photosynthesis ( photosystem II ) appeared in the early Archean 3.5 billion years ago, long before the appearance of the first cyanobacteria and the oxygen catastrophe 2.45 billion years ago ^{[9] [10]} .