PAST AND FUTURE 21 



A question Rubey does not consider in his exposition 

 concerns the rate at which these contributions from 

 below to the ocean water masses have been delivered. 

 Dividing the total volume of water in the oceans — 

 1.3 X 10^'^ cubic meters through two billion years (a 

 conservative estimate for the age of the oceans) — one 

 finds the annual increment to have been on an average 

 .65 X 10'^ cubic meters, a small fraction of the present 

 annual rainfall over the planet's surface. There are, 

 however, strong reasons for assuming that this contribu- 

 tion from juvenile water may have varied considerably 

 in the course of geological ages and that it has reached 

 higher values than the average during epochs of in- 

 tensified volcanic and magmatic activity. 



More recently Roger Revelle, director of Scripps 

 Institution of Oceanography, has taken up the problem 

 of the origin of ocean water.- Revelle believes a large 

 part of the magmatic volatiles — water vapor, carbon 

 dioxide, and mineral acids — has been released from the 

 ocean floor itself through a process of recrystallization 

 of the underlying substratum. In the last 100 million 

 years of earth history a water layer over 3,000 feet deep, 

 according to Revelle, has been produced "from below." 

 With this release the ocean floor has sunk considerably, 

 so that no very great change in the water level has 

 occurred. Such a subsidence of the ocean floor would 

 explain the gradual sinking of the volcanic islands and 

 the present great depth of the mysterious guyots, the 

 truncated, flat-topped volcanic cones with wave-planed 



