Primitive Planetary Atmospheres 19 



(2) The enormous iron deposit of the pre-Cambrian some 2 x 10^ years ago 

 may mark the time of transition from a reducing to an oxidizing atmosphere, 

 as MacGregor [12] suggested. 



Attempts have been made in the writer's laboratories to find primitive sources 

 of hydrogen and to determine the relative abundance of deuterium in such 

 hydrogen. It was thought that fractionation of the hydrogen isotopes during 

 escape would occur and hence that primitive hydrogen would have less deuterium 

 than the hydrogen of the present oceans and that the difference in deuterium 

 content would give an indication of the total loss of hydrogen. No conclusive 

 decision in regard to this question has been deduced. 



THE ATMOSPHERE OF VENUS 



The atmosphere of Venus contains large amoimts of carbon dioxide above 

 the cloud layer estimated by Herzberg [13] as some lo^ cm atmospheres. No 

 water or oxygen has been detected. Some evidence has been found by Kozyrev 

 [14] for the presence of nitrogen and carbon monoxide. 



Recent data of Pettit & Nicholson [15] on the intensity of hght reflected and 

 absorbed in the 8-14 cm region indicate that the temperatures of the light and 

 dark hemispheres are 233 °K and 238 °K respectively, Adel [16] has given 

 reasons for believing that this radiation comes partly at least from higher tran- 

 sitions of the CO2 molecule and since this radiation is absorbed by great thick- 

 nesses of this gas, the radiation in this region probably originates fairly high in 

 the atmosphere and not at the cloud level. From the distribution of intensity 

 in the P & R branches of the 7820 and 8689 Â bands of CO2 Chamberlain & 

 Kuiper [17] estimate a temperature of 285 °K, Their measurements refer to 

 regions well away from the mid solar point. Since these bands are partly absorbed 

 by the atmosphere the temperature must be some average for all the gas above 

 the clouds at the positions investigated. Mayer, Stoanaker & McCollough [18] 

 have reported a temperature greater than 350 °K by observations on the 3-15 cm 

 radiation. Possibly this radiation comes from the surface of the planet, though 

 this point is uncertain. 



From the standpoint of the question as to whether life exists on the planet, 

 the problem of the presence of water on the planet is of paramount importance 

 for no life as we know it exists in the absence of condensed water, and though 

 many terrestrial plants grow in very dry places and conserve their hquid water, 

 it is very difficult to believe that hfe could have evolved in the absence of copious 

 amounts of Hquid water. 



The planet is covered with clouds of a slightly yellow colour which show marked 

 absorption in the blue and near ultraviolet [14], These clouds clear slightly and 

 permanent surface markings have been observed by Danjon [19] and Dollfus [20]. 

 If conditions were similar to those of the Earth, nearly all carbon dioxide would 

 have reacted with the silicate rocks and form limestone, dolomite and sand [9], 

 Whipple & Menzel [21] suggest that the planet is completely covered by oceans 

 so that no effective contact between rocks and carbon dioxide exists, Urey 

 assumed that no water existed and hence erosion was ineffective in making con- 

 tact between carbon dioxide and the rocks, Danjon's and Dollfus' observations 



