100 LECTURES ON BIOLOGY 



a natural, law-governed development. At what period in the 

 earth's history life appeared for the first time and what were 

 the external conditions will always remain a matter of specu- 

 lation. Nevertheless, the attempt to form an idea of the con- 

 ditions which then existed might not prove entirely futile. Let 

 us, therefore, return in imagination to the original state of our 

 earth, to the time when it was a sphere of incandescent gases. 



It is known that very high temperatures suspend all chemical 

 compounds and decompose them into their single elements. We 

 must, therefore, assume that this glowing nebular mass contained 

 within itself all the numerous constituents disintegrated into the 

 last elements, which build up the earth and all objects at present 

 upon it. It is even conceivable that, seeing the enormous tem- 

 peratures which then existed, the substanceswhich we regard at 

 the present state of our knowledge as being incapable of further 

 division i.e., carbon hydrogen, oxygen, nitrogen and sulphur 

 or, iron, lead, gold and silver were decomposed into still more 

 elementary substances. This fiery ball, continually emitting its 

 heat into the icy space, continually lost warmth ; thus slowly 

 but steadily the cooling process went on. Then came the time 

 when the first chemical compounds came into existence, followed 

 by the period of the formation of a strong earth-crust. Never- 

 theless, we must assume that the temperature of the earth and 

 the gases surrounding it the atmosphere was at that time yet 

 so high that water could only be present in the atmosphere in a 

 gaseous form. 



The period of the formation of the earth-crust was probably 

 followed by a very long waterless period. When afterwards, 

 corresponding to the continued loss of heat, water became 

 deposited on the solid earth-crust and when this primeval 

 ocean had further cooled there were then at last present the 

 conditions of the possibility of existence of organisms like those 

 that exist to-day. But who would venture to say what enormous 

 periods of time had to elapse even then before the first life 

 appeared on the earth? It is possible to defend with good reason 

 the assumption, though it may appear at the first glance as a 

 contradictio in adjecto, that there first followed a time in which 

 organic compounds were formed before plants and animals came 

 into existence. 



