The Original Home of Life 7 



living matter came into existence many times, probably always in 

 the sea where there was appropriate temperature and when the sea 

 water was more dilute than now. Allen (1923) also maintains that 

 life arose in the sea and stresses the importance of photocatalysts 

 acting on water, carbon dioxide, and simple compounds of nitrogen. 

 Richardson (1928) pictures the origin of life in tropical intertidal 

 pools along rocky seashores, and emphasizes colloids and pigments 

 as factors. Flattely & Walton (1922) say "the shore has strong 

 claims to be recognized as the birthplace of life," and cite the lit- 

 toral region as "the cradle of evolution." 



Woodruff (Barrell et al., 1924) has reviewed various theories of 

 the origin of life. 



The Sea as the Original Home of Life 



In the oldest strata of sedimentary rocks which contain fossils 

 the remains of plants and animals all appear to be marine. This 

 indicates that life immediately before that time probably existed 

 largely or wholly in the ocean. This of course does not preclude the 

 possibility that life previously existed on land or in fresh water and 

 became extinct without leaving records as fossils. However, "at the 

 very begining of the Paleozoic Era are found all of the main kinds 

 of marine animals other than fishes" (Schuchert, in Barrell et al., 

 1924) . The invertebrates had been in existence during the preced- 

 ing eras (Archeozoic, Proterozoic) long enough for the chief types 

 as they exist at present to become established. As time went on 

 many of the older types (trilobites, etc.) became completely extinct 

 and new types (chordates, etc.) came into existence. As evolution 

 progressed, certain animals that were related to early chordates (os- 

 tracoderms, arthrodires, etc.) and some that were clearly chordate 

 (cyclostomes, elasmobranchs) appeared in the ocean, but most of 

 them and the bony fishes apparently had their origin in fresh water 

 (Barrell, 1916; Noble, 1931; Bigelow, 1931; Romer, 1945). 



