64 V. A. SOKOLOV 



the first place, CHj, N-j, CO and the rare gases, and later COj and small quan- 

 tities of HjS and NH:j. Such gases as NH3, HjS and, to a considerable extent, 

 CO2, took part in chemical reactions during their migration within the crust 

 of the Earth and dissolved in water, so their concentrations in the atmosphere 

 were small. 



The next, or third stage may be referred to as transitional, in reference to the 

 transition from the reducing to the oxidizing state of the atmosphere. 



Through volcanoes and in other ways, such gases as CO2, CO, N2, CH4, Ho, 

 NH3, HoS and the rare gases continued to be given off into the atmosphere. 

 During both this and the preceding stage, radiochemical and chemical processes 

 led to the formation of oxygen from those oxides of which the crust of the Earth 

 essentially consists. The chemical activity of the oxygen, however, hindered its 

 emission into the atmosphere. During its migration within the crust of the Earth 

 the oxygen oxidized those substances which it encountered there. Such oxygen 

 as reached the atmosphere there oxidized hydrogen and its compounds (CH4 

 etc.). The presence of hydrogen and some of its compoimds in the first and 

 second stage thus precluded any considerable accumulation of oxygen in the 

 atmosphere. 



During the course of the third stage the No, COo and CO given off from the 

 interior of the Earth accumulated in the atmosphere owing to the preferential 

 loss from it of the light gases such as H2 and CH4. As the solution of CO2 in 

 the waters of the surface of the Earth and its reaction with silicates lowered its 

 concentration in the atmosphere, the main components of the atmosphere came 

 to be the chemically inert nitrogen, with a greater or less admixture of carbon 

 dioxide and a small admixture of methane and other gases. It may also be that 

 small amounts of oxygen made their appearance in excess of the amoimts used 

 in oxidizing carbon monoxide and methane. 



The fourth, or biogenic stage in the evolution of the atmosphere of the Earth 

 is associated with the appearance and development of plant-Uke organisms. The 

 biochemical taking up of CO2 and giving out of O2 led to a considerable accumu- 

 lation of O2 in the atmosphere. The continued emission of CO2, No, the rare 

 gases and others from the interior of the Earth gave the atmosphere its present 

 characteristics. The taking up of COo by plants and the laying down of organic 

 residues in sedimentary formations has led to a transfer of the carbon of CO2 

 from the atmosphere to these sedimentary formations. 



Only a very small amount (2-4%) of the oxygen given off during this process 

 is present in the present-day atmosphere. The remainder would appear to have 

 been put out of circulation by the oxidation of the minerals of the superficial 

 layers of the crust of the Earth, and possibly part of it was lost. Such gases as 

 CO, H2, CHi and hydrocarbons containing two or more carbon atoms were 

 oxidized by oxygen in the atmosphere. CO2 and HoO were thus formed. The 

 carbon of the atmosphere (in the form of CO2) and also the nitrogen, took part 

 in cycUc processes associated with living material. The gases given off from the 

 interior of the Earth (H2S, SO2, NH3, CI, HCl, etc.) underwent oxidation and 

 entered into various chemical combinations. 



In the scheme of the evolution of the atmosphere just enunciated, the primary 



