Hi Elton, Steve, and List, The reason we don't see a similar amount of water on the Moon is due in part to insufficient gravitation. The Moon doesn't have the ability to retain water vapor and volatiles like the Earth does. Secondly, the Moon is a smaller target and probably suffered fewer water-bearing impacts.
The Earth's water is due to a combination of factors, including cometary bombardment, and local processes like volcanism. And, it's a known fact, that Mother Nature left the tap running for several million years, resulting in a larger volume of water on the planet's surface, and a massive water bill that took her thousands of years to pay off. Best regards, MikeG -- ------------------------------------------------------------- Web - http://www.galactic-stone.com Facebook - http://www.facebook.com/galacticstone Twitter - http://twitter.com/GalacticStone Pinterest - http://pinterest.com/galacticstone RSS - http://www.galactic-stone.com/rss/126516 ------------------------------------------------------------- On 10/3/12, Steve Dunklee <steve.dunk...@yahoo.com> wrote: > If the oceans were from comet impacts both the moon and mars would have > similar amounts of water. Or shall we delve into the atmosphere of Venus? > Things at the beginning of the system were most probably interesting. why > not just accept it was random bombardment and outgassing from solar > radiation which caused a variety of planets and planetismals. > > --- On Wed, 10/3/12, MstrEman <mstre...@gmail.com> wrote: > >> From: MstrEman <mstre...@gmail.com> >> Subject: [meteorite-list] Critical Assessment of the Comet as Provider of >> Earth's Waters >> To: "Meteorite-list" <meteorite-list@meteoritecentral.com> >> Date: Wednesday, October 3, 2012, 6:53 AM >> What do we know about the origin of >> the earth's oceans? Is it more >> likely that they derive from icy comets that struck the >> young earth or >> from material released from the earth's interior during >> volcanic >> activity? >> >> Full Article at >> <http://www.scientificamerican.com/article.cfm?id=what-do-we-know-about-the> >> >> Tobias C. Owen of the Institute for Astronomy in Honolulu, >> Hawaii, >> offers this overview: >> "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 planetesimals. >> 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. >> >> "The composition of the ocean offers some clues as to its >> origin. If >> all the comets contain the same kind of water ice that we >> have >> examined in Comets Halley and Hyakutake- -the only ones >> whose water >> molecules we've been able to study in detail-- then comets >> cannot have >> delivered all the water in the earth's oceans. We know this >> because >> the ice in the comets contains twice as many atoms of >> deuterium (a >> heavy isotope of hydrogen) to each atom of ordinary hydrogen >> as we >> find in seawater. >> >> "At the same time, we know that the meteorites could not >> have >> delivered all of the water, because then the earth's >> atmosphere would >> contain nearly 10 times as much xenon (an inert gas) as it >> actually >> does. Meteorites all carry this excess xenon. Nobody has yet >> measured >> the concentration of xenon in comets, but recent laboratory >> experiments on the trapping of gases by ice forming at low >> temperatures suggest that comets do not contain high >> concentrations of >> the xenon. A mixture of meteoritic water and cometary water >> would not >> work either, because this combination would still contain a >> higher >> concentration of deuterium than is found in the oceans. >> >> "Hence, the best model for the source of the oceans at the >> moment is a >> combination of water derived from comets and water that was >> caught up >> in the rocky body of the earth as it formed. This mixture >> satisfies >> the xenon problem. It also appears to solve the deuterium >> problem--but >> only if the rocky material out near the earth's present >> orbit picked >> up some local water from the solar nebula (the cloud of gas >> and dust >> surrounding the young sun) before they accreted to form the >> earth. >> Some new laboratory studies of the manner in which deuterium >> gets >> exchanged between hydrogen gas and water vapor have >> indicated that the >> water vapor in the local region of the solar nebula would >> have had >> about the right (low) proportion of deuterium to balance the >> excess >> deuterium seen in comets. >> >> "The point to emphasize here is that this is a model, a >> working >> hypothesis that must be rigorously tested by many >> additional >> measurements. We need to study more comets. We also need to >> learn more >> about the water on Mars, where we have another chance to >> investigate >> the sources described above. On the earth, plate tectonics >> has caused >> oceanic water to mix considerably with material from the >> planet's >> interior; such contamination probably did not occur on Mars, >> where >> plate tectonics does not seem to occur. These investigations >> (and >> other related studies) are currently under way. This is an >> active area >> of research!" >> >> James C. G. Walker of the University of Michigan confirms >> that >> conclusion, adding his perspective: >> >> "The best current thinking is that volatiles (elements and >> compounds, >> including water, that vaporize at low temperatures) were >> released from >> the solid phase as the earth accreted. Thus, the earth and >> its oceans >> and atmosphere grew together. >> >> During accretion, the kinetic energy of the colliding >> planetesimals >> was converted into thermal energy, so the earth grew >> extremely hot as >> it came together. The material forming the earth was >> probably too hot >> for ice to have been a major carrier of water. Most of the >> water was >> probably present originally as water trapped in clay >> minerals or as >> separate hydrogen (in hydrocarbons) and oxygen (in iron >> oxides), >> rather than as ice. "Since the end of the period of >> accretion, more >> than four billion years ago, there has been a continual >> exchange of >> volatile material--including water--between the surface of >> the earth >> and the planet's interior (that is, between the crust and >> the mantle). >> Volcanoes release water and carbon dioxide to the atmosphere >> and >> ocean. Subduction of sediments rich in volatiles takes place >> at deep >> ocean trenches. The sinking of oceanic crust at subduction >> zones >> carries water and carbon dioxide back into the mantle. These >> processes >> can all be seen at work today. >> >> In short, icy cometary material probably has not been >> important in >> providing water for the earth's oceans, but there is little >> sure >> knowledge in this field. " >> >> Elton >> ______________________________________________ >> >> Visit the Archives at >> http://www.meteoritecentral.com/mailing-list-archives.html >> Meteorite-list mailing list >> Meteorite-list@meteoritecentral.com >> http://six.pairlist.net/mailman/listinfo/meteorite-list >> > > ______________________________________________ > > Visit the Archives at > http://www.meteoritecentral.com/mailing-list-archives.html > Meteorite-list mailing list > Meteorite-list@meteoritecentral.com > http://six.pairlist.net/mailman/listinfo/meteorite-list > ______________________________________________ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
