60 The Outline of Science 



tender plant we call LIFE. There are very tough living crea- 

 tures, but the average organism is ill suited for violence. Most 

 living creatures are adapted to mild temperatures and gentle 

 reactions. Hence the fundamental importance of the early 

 atmosphere, heavy with planetesimal dust, in blanketing the 

 earth against intensities of radiance from without, as Chamberlin 

 says, and inequalities of radiance from within. This was the 

 first preparation for life, but it was an atmosphere without free 

 oxygen. Not less important was the appearance of pools and 

 lakelets, of lakes and seas. Perhaps the early waters covered the 

 earth. And water was the second preparation for life water, 

 that can dissolve a larger variety of substances in greater con- 

 centration than any other liquid; water, that in summer does 

 not readily evaporate altogether from a pond, nor in winter 

 freeze throughout its whole extent; water, that is such a mobile 

 vehicle and such a subtle cleaver of substances; water, that 

 forms over 80 per cent, of living matter itself. 



Of great significance was the abundance of carbon, hydro- 

 gen, and oxygen (in the form of carbonic acid and water) in the 

 atmosphere of the cooling earth, for these three wonderful ele- 

 ments have a unique ensemble of properties ready to enter into 

 reactions and relations, making great diversity and complexity 

 possible, favouring the formation of the plastic and perme- 

 able materials that build up living creatures. We must not 

 pursue the idea, but it is clear that the stones and mortar of 

 the inanimate world are such that they built a friendly home 

 for life. 



Origin of Living Creatures upon the Earth 



During the early chapters of the earth's history, no living 

 creature that we can imagine could possibly have lived there. 

 The temperature was too high; there was neither atmosphere 

 nor surface water. Therefore it follows that at some uncertain, 

 but inconceivably distant date, living creatures appeared upon 



