Sodium (for the sodium chloride, common table salt, which is the most abundant in the oceans) could have reached the waters from the rocks of the Earth, but chlorine is much rarer, and may be extraterrestrial in origin (not ET, just from debris hitting the Earth).
Small Comets and Our Origins
University of Iowa | circa 1999 | Louis A. Frank
Posted on 10/20/2004 2:13:25 AM EDT by SunkenCiv
http://www.freerepublic.com/focus/f-bloggers/1250694/posts
so enuf comets of sodium all at a soon enuf time to salinate the ocean, why are they not still acomin asalinating?