40 Proceedings of the Ohio State Academy of Science 



The planetesimal hypothesis gives a wholly new explanation 

 of the atmosphere and of the oceans. The material of both was 

 brought in dissolved or occluded in the infalling planetesimals, 

 just as now the meteorites contain three to four times their 

 volume of dissolved gases. With the later development of high 

 temperatures these gases made their escape to the surface, and 

 after the earth became large enough for gravity to overcome the 

 tendency of the gaseous molecules to fly off into space an atmos- 

 phere and later a hydrosphere came into existence. In this case 

 oceans may have existed on the earth well before it attained its 

 present size. Life, too, may have come into existence at a very 

 early stage, as soon as conditions of air and water were such as 

 to support living beings. 



The future of the Planetesimal hypothesis no one can fore- 

 cast. The hypothesis of La Place held almost undisputed sway 

 for a century. Perhaps this newer one will iji its turn oass. O^. 

 more or less modified, it may finally establish itself as a better 

 statement of our earth's- earlier history. I wish only to point out 

 that it gives a fundamentally dift'erent interpretation of this earlier 

 history and of the forces which are at work within the globe as a 

 whole, and that this new interpretation must modify, indeed, al- 

 ready has modified our thinking on the great fundamental 

 problems of geology. Our conception of the causes of volcanic 

 action, of all movements of the earth's crust, from the great 

 periodic readjustments between continents and oceanic segments, 

 with their accompaniments of mountain folding and plateau 

 formation, to the slighter movements which are constantly pres- 

 ent, of the origin of the great complex of rocks which makes up 

 the Archean ; — our conception of the causes of all of these and of 

 many minor geological matters, is profoundly different on the two 

 hypotheses. Many of them seem much clearer on the newer than 

 on the older theory. 



IN CONCLUSION. 



Several matters of human interest come out in the progress 

 of this paper. I have already mentif^neJ the control which local 

 geological phenomena exert over geological theory, in speaking of 



