254 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 40 



It is difficult for us, overwhelmed by the complexity of evolution, 

 to single out those features which are most distinctive of life, but 

 suppose we hand the problem over to reasonable beings of our imagi- 

 nation, who, coming from a world such as ours, but on which life 

 has never existed, view for the first time the earth. We may 

 imagine them to be physicists or chemists or even mathematicians, 

 for obviously no biologist could come from a lifeless world! 



Among many wonders, two things would strike these visitors as 

 outstandingly peculiar. The first concerns the structure of the 

 earth's crust. In it occur unlikely accumulations which would have 

 no counterpart in a lifeless world. Average sea water contains only 

 0.12 part of calcium carbonate per thousand, yet some 48 millions of 

 square miles of the ocean floor are covered with a deep deposit of 

 calcareous ooze containing calcium carbonate up to 90 percent. The 

 coral islands of modern seas, the chalk and limestone formations 

 which represent relics of the oceans of geologic times and which 

 make up a very considerable part of the solid crust upon which we 

 live, have been similarly abstracted and assembled by living animals 

 from sea water. Soluble silica occurs in very minute quantities in 

 the ocean, never exceeding 1.5 parts per million, yet in our present- 

 day oceans plants have assembled from such a dilution, 10 millions 

 of square miles of diatom ooze, and radiolarian ooze accounts for 

 another 2 millions of square miles of siliceous accumulations; 



From the atmosphere, as well as from the ocean, unlikely aggre- 

 gates have been sorted out. The average proportion of carbon 

 dioxide in the lower atmosphere is about 3 parts per 10,000, yet the 

 superficial deposits of peat and the deeper formations of coal, oil 

 shale, and the natural petroleum produced from them, consist essen- 

 tiallv of carbon sorted out by plants from that tenuous store. The 

 carbon dioxide, dispersed and inert, in 16,125,000 cubic yards of air 

 is gathered and made potentially efficient by a single tree of some 5 

 tons dry weight. 



To us these aggregates have lost all sense of wonder, but to our 

 physicists from a lifeless world they must seem as unbelievable as 

 the giraflPe to the youngster at the zoo, for they controvert one of 

 the established laws of physical order, that, left to themselves, units 

 of matter in a gas or a solution move toward their maximum dis- 

 persal. The normal physical course of dispersal in the cases I have 

 mentioned has been replaced by assortment and aggregation, and the 

 agent of the reversal has been the living organism. 



The second stumbling-block over which our visitors would trip in 

 their prospect of the earth is supplied by the history of living 

 things themselves. The life history of any multicellular organism 

 i§ j^ development, that is a selection and reassortment of material^ 



