HYDROCARBONS FORMED A B lO GEN I C ALL Y 125 



Here too, as in other heavenly bodies, we find hydro- 

 carbons, as was to be expected from a theoretical considera- 

 tion of the circumstances under which comets were formed. 



In the light of all that has gone before we see that not only 

 is it perfectly possible that hydrocarbons could have been 

 formed abiogenically under natural conditions but this pro- 

 cess seems to be extremely widespread throughout the uni- 

 verse. Hydrocarbons have been found everywhere, on all 

 bodies accessible to investigation ; in the atmosphere of stars 

 of different spectral types, particularly in the atmosphere of 

 the Sun ; in the cold clouds of gas and dust in interstellar 

 space ; on the surfaces of the large planets and their satellites, 

 in the substance of comets and, finally, in meteorites falling 

 on the surface of the Earth. Is it possible that our planet 

 is an exception to this general rule and that the simplest 

 organic substances could never have arisen abiogenically on 

 it? Is it not more probable that this process took place in 

 the past before the appearance of life on the Earth and 

 perhaps still goes on although we do not notice it? 



Geological finds of hydrocarbons 

 formed abiogenically on the Earth. 



Most astronomers and geologists believe that in the centre 

 of the Earth, at a depth of 2,900 km., there is a nucleus 

 which is far denser than the superficial formations and which 

 is similar in chemical composition to the metallic (iron) 

 meteorites. This consists, for the most part, of iron and 

 nickel, with a small admixture of cobalt and other elements. 

 If it is assumed that carbon is present in the core of the 

 Earth, it is present there in the form of carbides of iron and 

 nickel similar to those in the iron meteorites (Fig. 9). 



On the other hand, O. Shmidt^^ and a number of his 

 colleagues at the Geophysical Institute of the Academy of 

 Sciences of the U.S.S.R. consider that the outer parts of the 

 Earth and its core do not differ from one another in their 

 chemical composition but only in their physical state. Accord- 

 ing to Shmidt the differences in density, seismic and other 

 phenomena which have led people to postulate a nucleus in 

 the Earth could be due to phase transformations of siliceous 

 material into the metallic state brought about by the high 



