56 V. A. SOKOLOV 



Temperatures of the order of looo °C prevailed in the deep zones of the Earth 

 in earlier epochs too. Heat was lost from these deep zones by the emission of 

 hot gases, lava and water during volcanic activity, and by thermal conduction 

 by the crust of the Earth. 



From the point of view of those who hold that the Earth was formed at low 

 temperatures, conditions on it were favourable to the retention of numerous 

 substances which, when the temperature rose, provided the necessary conditions 

 for the formation of an atmosphere and a hydrosphere. If we assume that the 

 Earth existed for a long time in a completely molten state at a temperature of 

 some thousands of degrees, then, it is clear that light gaseous substances, and 

 even water, would have been almost completely lost and thus there could not 

 have occurred the enaission of vapours and gases from volcanoes, such as is 

 seen now and occurred in earlier times. 



Thus, a number of different considerations tell against the idea that the atmos- 

 phere and hydrosphere of the Earth were formed as a result of its complete 

 melting with a subsequent condensation of water. It would seem more satis- 

 factory to suppose that there was a gradual emission of gases and water vapour 

 during the whole course of the history of the Earth. 



Let us consider the history of the atmosphere of the Earth starting from the 

 hypothesis that the temperature of its surface was low. 



At low temperatures (10-20 °K) such as may have prevailed in the proto- 

 planetary envelope of the Earth, only hydrogen and helium can exist in the 

 gaseous state. All the other elements and their compounds are soUds at such 

 temperatures. 



As is well known, the speed for escape of gases amounts, in the case of the 

 Earth, to about 11-3 km/sec and the root-mean-square speed of gaseous mole- 

 cules at different temperatures changes in proportion to \/T. According to the 

 calculation of Jeans, the retention of the atmosphere of a planet is assured under 

 conditions in which the root-mean-square speed of the molecules does not 

 exceed 0-2 x the speed for escape. 



However, the actual conditions for the dissipation of gases from the atmosphere 

 seem to be more complicated in that, at great heights, owing to the ratification 

 of the atmosphere, the atomic state of the gases and the action of the rays of the 

 Sun, the molecules and atoms of these gases can attain considerable speeds, 

 corresponding to a temperature of some hundreds of degrees or perhaps even 

 more. 



A study of the composition of the present-day atmosphere shows a minute, 

 insignificant concentration of such inert gases as Ne, Kr and Xe. According to 

 the hypothesis which we have discussed these gases were lost from the primary 

 atmosphere. It has been shown by V. G. Fcsenkov that, during its escape, 

 hydrogen may carry other gases away from the atmosphere with it. The condi- 

 tions for the loss of gases would seem to be determined by other factors as well 

 as their temperature [7-10]. In this connection it has been held that, during the 

 formation of the Earth, the primary atmosphere was lost and that later, owing 

 to the heating of the Earth and the consequent formation of gases, a new, 

 secondary atmosphere made its appearance. 



