Posted by arleneteng on November 30, 2009 at 6:34 AM
by Tobias C. Owen, Institute for Astronomy in Honolulu, Hawaii
This is a very good question, because we do not yet have an answer that everyone accepts.
The origin of the oceans goes back to the time of the earth's formation 4.6 billion years ago, when our planet was forming through the accumulation of smaller objects, called planetesimials. There are basically three possible sources for the water. It could have (1) separated out from the rocks that make up the bulk of the earth; (2) arrived as part of a late-accreting veneer of water-rich meteorites, similar to the carbonaceous chondrites that we see today; or (3) arrived as part of a late-accreting veneer of icy planetesimals, that is, comets.