CHAPTER XX 

 FOSSIL ANIMALS 



Not all the animal kinds that have lived on this' earth 

 still live on it. Indeed those that now exist, as many hun- 

 dred thousands.or millions as they may be, are certainly only 

 a small part of all that have existed. The farth has had 

 a history of life as varied and nearly as old as the history 

 of its own liquid and solid self. As soon as it had cooled 

 and contracted from a great gaseous mass to a smaller com- 

 pacter liquid and solid one it began to be a possible abode of 

 life. And sometime after its temperature had got below the co- 

 agulation or killing point for protoplasm — ^which is the basic 

 substance of every living thing — life appeared. Whence it 

 came or how it came to be produced are great questions that 

 science has yet no answer for and may never have. The 

 speculations about it are various: such as that living germs 

 reached the earth from other planets in meteorites or as 

 "cosmic dust," or that it originated spontaneously under 

 the peculiar chemical and physical conditions of the earth's 

 surface in those ancient dim days of the first hardening and 

 cooling. And there are even some biologists who think that 

 such spontaneous generation of life from non-living sub- 

 stances may be going on today. But no one of them has 

 been able to prove this. "All life froin previous life" is 

 the dictum of most naturalists of today. And this poses the 

 problem of the origin of the first life as one far beyond 

 present scientific knowledge. , ; , 



If, however science knows nothing about the origin of life 

 in the early days of the earth's history it does know something 



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