The Evolution of the Atmosphere 

 of the Earth 



V. A. SOKOLOV 

 Petroleum Institute of the Academy of Sciences of the U.S.S.R., Moscow 



The problem of the evolution of the atmosphere of the Earth has attracted much 

 attention in recent years both in connection with the new cosmogonie hypotheses 

 concerning the formation of the Earth [1,2] and in connection with the problem 

 of the origin of life [3-5]. 



From contemporary scientific evidence one may, it seems, draw the most 

 generally accepted conclusion, that the Earth, Hke the other planets, was derived 

 from a cloud of dust and gas which lay in an equatorial plane round the Sun. 

 The substance of the Earth, like that of the other planets, is closely associated 

 with the substance of the primitive Sun. The age of the substance of the Earth 

 is estimated at 5000-7000 million years. 



Assuming that this view is correct, the composition of the gas in the cloud of 

 dust and gas must have corresponded with the composition of the outer layers 

 of the Sun at the time when it was formed by condensation. 



The interstellar medium itself is well known to contain a very rarified gas 

 (lO"-* g/cm^) composed mainly of hydrogen (about 90"^,) and helium (about 9°ô)- 

 The quantity of such elements as oxygen, carbon, nitrogen and neon in the gas 

 amounts, in all, to about 1%, while all the other elements together, mainly 

 iron, sihcon, magnesium, sulphur, etc., account for only about o-2-o-3"y. The 

 interstellar gas contains not only elements, but also their compounds. 



Hydrogen and helium predominate in the atmosphere of the Sun at present. 

 All the rest of the elements only constitute about 1-2" (, of it and among these, 

 according to the evidence of spectrographic analysis, O, Mg, N, Si, C, S and Fe 

 are present in by far the greatest concentrations. A high concentration of light 

 gases, e.g. H2, CHj and NH3, may be observed in the atmospheres of the large 

 planets of the solar system. 



During the condensation of the cloud of dust and gas there took place a 

 differentiation of its substance, with the formation of the denser, heavier nuclei 

 of the incipient planets and their somewhat lighter surrounding envelopes. This 

 is the period at which we may properly consider the history of the Earth to have 

 started. The primary atmosphere undoubtedly contained H and He. As to other 

 elements and compounds, their presence in the atmosphere depended on the 

 temperature. 



Different opinions have been expressed as to the temperature of the Earth 

 at the time of its formation. Some investigators have thought that its tempera- 

 ture was very low, others that it was so high that the Earth was, so to speak, in 

 a molten state. 



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