No. 56: Mar-Apr 1988
In keeping with the foregoing extraterrestrial flavor, we are happy to report that our oceans may be exogenous; that is, derived from extraterrestrial materials. Once again, comets seem to be the culprits. C.F. Chyba has examined the lunar impact record and derived an estimate of the total mass of objects impacting the moon during the (hypothetical) period of heavy bombardment 3.8 to 4.5 billion years ago. This allowed him to calculate the mass influx for the earth during this period. His conclusion: if only about 10% of the incoming mass consisted of comets (mostly ice), the earth would have acquired all its ocean water.
(Chyba, Christopher F.; "The Cometary Contribution to the Oceans of Primitive Earth," Nature, 330:632, 1987.)
Comment. Frank claims that the earth today is continually bombarded by small icy comets, which down the eons may have kept the ocean basins full. So, we have two possible extraterrestrial sources of oceans -- both of a cometary nature. It was only yesterday that the idea of ice surviving in outer space was ridiculed; no one even dreamed that our oceans could be composed of space ice!