490 THE THEORY OF EVOLUTION 



bearing rocks is to be reckoned in hundreds of millions of years, 

 and since the original organisms must have antedated any fossil 

 remains by a considerable period (Fig. 259). There must have 

 been a time when the earth was too hot to support anything 

 resembling protoplasm as we know it to-day. Protoplasm must 

 have appeared during the period between this heated state and the 

 time of the earliest fossils, after suitable environmental conditions 

 had arisen. If the age of the Cambrian fossils is as great as 800,000,- 

 000 years, as some geologists now believe, organisms may have 

 come into existence 1,500,000,000 years ago. In arriving at such a 

 conclusion one must have due regard for the limitations of all 

 attempts to estimate geologic time. What can be said with 

 certainty is that protoplasm has existed upon our planet for a very 

 long period, as shown by the record in the rocks, and that it was 

 presumably in existence for a long time before the period of the 

 earliest fossils. In this connection it will be noted that the time 

 during which the higher animals, such as the vertebrates, have 

 been in existence is a very small fraction of the entire history 

 of life. 



Manner of Origin. — Here again, one must have recourse to 

 speculation, based upon facts that suggest possibilities. Accord- 

 ing to the Cosmozoic Theory, or, as it might be called, the " Infec- 

 tion Hypothesis," the original germs of protoplasm accidentally 

 reached the earth from some other body in space. A simple form 

 of protoplasm thus " infected " a waiting planet, much as germs 

 infect a test-tube containing a sterile medium fit for their develop- 

 ment. It might be supposed that the primeval organisms arose 

 from such an original infection, and that by evolutionary develop- 

 ment there were produced the vast array of plants and animals that 

 have since existed. This theory is unsatisfactory because it does 

 not explain how the protoplasm originated, which is the real ques- 

 tion at issue. The problem is sufficiently remote from any possible 

 solution, if the origin of life is traced to the early stages of our 

 earth. It becomes hopeless if removed to some other body in 

 time and space, since there still remains the question of how life 

 could have come into existence in some other part of the universe. 

 Moreover, it may be objected that the infecting germs could hardly 

 have survived the low temperature of interstellar space ; nor could 

 they have survived the heat generated by bodies entering the 

 atmosphere. The possibility that such a " cosmic rain " of germs 



