Has there ever been an estimate made of the number of strikes needed to deliver the volume of water currently on Earth? I have to think it's enormous.
have a look at the image in this link:
>>A reservoir of water three times the volume of all the oceans has been discovered deep beneath the Earth's surface. The finding could help explain where Earth's seas came from.
http://www.newscientist.com/article/dn25723-massive-ocean-di...
Note: at extreme temps and pressures in the core, water as we know it is not a good guidepost. It may be crystallized or associating strongly with other exotic crystals and 'plastic'-y compounds at the Moho layer and other transition zones deep down. Also, just counting O and H elements is likely to not get you far there either. The story of how we got our oceans is FAR from complete. I'd wager we are in the 2nd page of the prologue though, which, for 60 years of real work, is pretty good compared to most fields.