The Origin of Organic Molecules 11 



Development of other planets 



It is evident that the processes outlined ahove could occur on other 

 planets than the earth. But first, nearly all of the solar components 

 of gases must he lost and then conditions must he such that hydrogen 

 can escape at a sufficiently slow rate for the synthesis of very complex 

 carhon compounds to occur. It is possible and indeed probable that 

 this has occurred very generally throughout the entire universe, and 

 it is possible that it has occurred on both Venus and Mars. At present 

 both these planets have carbon in the highly oxidized state of carbon 

 dioxide in their atmospheres, though elementary oxygen has not been 

 detected in either; on the other hand, neither has the highly reduced 

 form of carbon, namely, methane, been detected. 



The atmosphere of Venus contains about 1 km atmosphere of car- 

 bon dioxide above the cloud layer. Aside from a very small amount of 

 water vapor, no other gas has been. detected with certainty in its 

 atmosphere. Several explanations have been offered for the presence 

 of large amounts of carbon dioxide in spite of the affinity of carbon 

 dioxide for silicate rocks which favors its presence as limestone of 

 dolomite. (1) The surface of the planet is arid so that erosion is 

 negligible; hence contact between the gas and solid rocks is ineffective 

 and an equilibrium condition is not approximated. (2) The surface 

 of the planet is covered by oceans and again effective contact is not 

 possible. (3) An excess of carbon dioxide exists such that all surface 

 silicates have been converted to carbonates and the atmospheric 

 carbon dioxide remains in the uncombined state. (4 I The tempera- 

 tures below the atmosphere are so high that the equilibrium pressure 

 is much higher than that appropriate to the earth. The surface tem- 

 peratures as reported at present are consistent with the first and third 

 alternatives only. It has also been suggested that an excess of hydro- 

 carbons exists and that the surface is covered with oceans of petro- 

 leum-like compounds. The temperature in the high atmosphere from 

 infrared measurements is reported to be some — 40°C. From the 

 intensities in the rotational spectrum of visible carbon dioxide bands, 

 the temperature is observed to be some 10 or 15C. But the intensity of 

 the radiation in the centimeter wavelength region indicates tempera- 

 tures in the region of 300°C. It appears that the first two temperatures 

 must be characteristic of some layers in the atmosphere above the 

 clouds, and the last temperature is generally thought to be that of the 

 solid surface. Sagan (1961) has given reasons for believing that a 

 very effective "greenhouse effect" due to carbon dioxide and water 

 may account for this high temperature. If these high temperatures 



