ORIGIN OF ORGANIC COMPOUNDS I37 



the peculiarities of the solar system, which have been men- 

 tioned abo\e, in this way. In connection with the solution 

 of the problem of the formation of the first organic com- 

 pounds, which is our present task, special interest attaches to 

 the chemical processes which went on during the formation 

 of the Earth and in the earliest stages of its existence. 



The investigations of G. P. Kuiper and the facts put for- 

 ward by H. C. Urey in his book The planets, their origin and 

 developtnejit^" are of special value in this connection. 



According to Urey the early chemical history of the Earth 

 and the other planets is determined by the follo^ving basic 

 factors (cf . Table i ) : — 



(1) The distribution of the elements in the cosmos, especi- 

 ally the composition of the primaeval solar nebula ; (2) the 

 temperatures which prevailed at the various periods of the 

 formation of the Earth ; (3) the gravitational field of a planet 

 in the course of its formation ; (4) the properties of the 

 chemical substances taking part in this formation. 



We may judge of the composition of the primaeval solar 

 nebula by studying the clouds of dust and gas which exist 

 at present. The predominant element here, as in the cosmos 

 in general, is hydrogen. Helium and the other inert gases 

 are also present, though in considerably smaller quantities. 

 Such elements as carbon, nitrogen, oxygen, iron, calcium, 

 silicon, etc., are present in proportions of 1 : 1,000, 1 : 10,000 

 or even less compared w^ith hydrogen. At the extremely lo\v 

 temperatures (near to absolute zero) which prevail in a 

 nebula, only hydrogen, the inert gases and methane can exist 

 in the gaseous state. Oxygen is present in the form of metallic 

 (iron) oxides and water, and nitrogen in the form of am- 

 monia. All these compounds exist in the nebula in the solid 

 state in the form of fine particles of dust ^\ hich also contain 

 silicates, metallic iron, iron sulphide, etc. 



Urey points out that all the free radicals of carbon, nitro- 

 gen and oxygen would be transformed into the stable mole- 

 cules CH4, NH3 and H.o on account of the catalytic action of 

 the dust and the presence of large amounts of hydrogen in 

 the nebula. There would also be formed from the free radicals 

 compounds of high molecular weight characterised by the 

 linkages c-c, n-n, n-c and c-o. 



