OCEANS AND THEIR HISTORY 13 



sea surface but which in a remote past afforded roads 

 for the migration of nonaquatic organisms across the 

 wide gulfs separating one continent from another. 



In general, it has been assumed that the Pacific Ocean 

 is the most ancient of all the seas, possibly a primary 

 feature of the earth's crust. Some theoreticians have even 

 gone so far as to suppose its basin to be the "birth scar" 

 left behind when our satellite, the moon, was torn out of 

 the earth's body by enormous tidal forces. Those who 

 had the privilege of listening to Harold Urey's masterly 

 exposition of the origin of the planets, and especially of 

 the earth and its moon, in the Silliman Lectures of 195 1 

 will remember on how slight a foundation this hypothe- 

 sis is based.- Nonetheless, the demand for a reconstruc- 

 tion of the Pacific basin which would satisfy paleontolo- 

 gists and biogeographers has found support among 

 eminent geologists like the late J. W. Gregory. The need 

 to postulate an ancient path of migration from northeast 

 Asia over the Hawaiian Islands to Central America has 

 led to the reconstruction of a hypothetical ancient land 

 bridge called Archigalenis. A similar bridge, called 

 Archinotis, has been suggested as a link between the 

 Antarctic Continent and South America. 



These and similar tamperings with the map of the 

 Pacific Ocean are not much favored by present-day 

 geologists. However, the evidence for an intercon- 

 tinental land bridge in the far North appears to be much 

 better founded. Behring Strait, which separates north- 

 east Siberia from northwest Alaska, is fairly narrow 



