256 ANNUAL REPORT SMITHSONIAN tNSTlTUTION, 1950 



circulation. These material constituents comprise the familiar chem- 

 ical elements, only a few of which, occurring in quantities of but a few 

 parts per million, are significantly radioactive. 



For the present discussion we shall restrict our attention to the non- 

 radioactive materials and shall summarily state that the events of our 

 interest are the result of a flux and degradation of a supply of energy, 

 and the corresponding circulation of matter regarded as consisting of 

 nontransmutable and indestructible chemical elements. 



All but a minute part of the energy involved in this process is that 

 derived from solar radiation, and a small fraction of the matter at 

 or near the surface of the earth occurs in the peculiar aggregates known 

 as living organisms. A part of the solar radiation incident upon the 

 earth serves to propel a circulation of matter into and out of this 

 organic assemblage. In this process an amount of energy roughly 

 proportional to the mass of the matter incorporated in organisms is 

 held in storage as chemical potential energy. 



From geological evidence, organisms have existed upon the earth 

 for probably as long as a billion years, during the last 500 million of 

 which a fraction of these organisms has become buried in the accumu- 

 lations of sediments under conditions which have prevented complete 

 disintegration and complete loss of their energy content. Conse- 

 quently, there exist in the sedimentary rocks of the earth today ac- 

 cumulations of the remains of fossil organisms in the form of coal, 

 oil shale, and petroleum and natural gas, which are rich in fossil 

 energy stored up from the sunshine of the past 500 million years. 

 This process of accumulation is doubtless still occurring, but the rate 

 is probably not very different from that of the past, so that, for an 

 order of magnitude, the accimiulation during the next million years 

 will probably not exceed one five-hundredth of the accumulation which 

 has occurred already. 



RISE OF HUMAN SPECIES 



With this background let us now consider the development of the 

 human species. From archeological and geological evidence it ap- 

 pears that a species recognizable as man must have existed roughly a 

 million years ago. The population of this species at that stage is un- 

 known but evidently was not large. It existed in some sort of eco- 

 logical adjustment with the rest of the organic complex, and competed 

 with the other members of the complex for a share of solar energy es- 

 sential to its existence. At that hypothetical stage its sole capacity 

 for the utilization of energy consisted in the food it was able to eat — 

 about 2,000 kilogram-calories per capita per day. 



Between that stage and the dawn of recorded history, this species 

 is distinfifuished from all others in its inventiveness of means for the 



