CHAPTER III 



THE PROTOVERTEBRATE 



The first episode of mountain building to leave a recog- 

 nizable geologic record was the Laurentian revolution, 

 some thousand million years ago, when molten granite 

 of volcanic origin poured over older sedimentary strata, 

 and these strata were themselves lifted and folded into 

 mountain chains. These Laurentian mountains are long 

 since gone but the sediments to which they were re- 

 duced remain exposed in areas in eastern Canada and 

 give name to this moimtain-building episode. After the 

 Laurentian came the Algoman revolution, then two 

 more, which are obscure, and then the Chamian, which 

 closed the ancient history of the earth— a period cover- 

 ing six-sevenths of its entire d^lration— and ushered in the 

 Paleozoic (palaios = ancient; zoe = life) era, five h\m- 

 dred and fifty million years ago, in which life first began 

 to leave indubitable traces of its existence. 



Speculations on the origin of life can be deferred un- 

 til more knowledge is available about the chemistry of 

 the ancient seas. There need have been nothing unique 

 about the circimistances attending its birth except that 

 protoplasm spun itself out of sunlight and the available 

 stuflFs of water and air, and operated according to the 

 laws of thermodynamics— with only this to distinguish it 

 from sea, wind, and rain: that by a favorable concatena- 

 tion of molecular forces it automatically became organ- 



