THE BEGINNINGS OF LIFE 



need not have been anything either sudden or 

 abnormal. 



When our earth, refusing to follow in their 

 retreat the heavier portions of the solar nebula, 

 began its independent career as a planet, its 

 surface was by no means so heterogeneous as at 

 present. We may fairly suppose that the tem- 

 perature of that surface cannot have been lower 

 than the temperature of the solar surface at the 

 present time, which is estimated at three mil- 

 lion degrees Fahrenheit, or some fourteen thou- 

 sand times hotter than boiling water. At such 

 a temperature there could have been no forma- 

 tion of chemical compounds, so that the chief 

 source of terrestrial heterogeneity did not ex- 

 ist ; while physical causes of heterogeneity were 

 equally kept in abeyance by the maintenance 

 of all things in a gaseous state. We have now 

 to note how the mere consolidation and cooling 

 of this originally gaseous planet must have 

 given rise to the endless variety of structures, 

 organic as well as inorganic, which the earth's 

 surface now presents. The origination of life 

 will thus appear in its proper place, as an event 

 in the chemical history of the earth. Let us 

 see what must have been the inevitable chemi- 

 cal consequences of the earth's cooling. 



In a large number of cases heat is favourable 

 to chemical union, as in the familiar instance 

 of lighting a candle, a gas jet, or a wood fire. 

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