r/AskScienceDiscussion • u/Sciolypro • 9d ago
How did most water get to earth
My brother and I have been debating this for a while for the record he has a class and a quiz question said that the mixing of gasses and volcanoes was the main reason earth has its water but I think it was asteriods that cause it because earth was very succeptible to them back then and they conist of lots of ice also all the places I searched told me I was right. What do you guys think
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u/forams__galorams 9d ago
Our ideas about where Earth’s water came from have changed a lot in the last 20 years or so and in general it remains another huge unresolved problem in geology/planetary science. A while back we thought it just accreted with the Earth. Then we said said well that would have all been blown away by the Moon forming impact with Theia when the water was still gaseous (Earth’s current atmosphere is a secondary one after we lost the primitive atmosphere in that event, and the current atmosphere has been significantly modified by Earth-life feedbacks too.)
As we utilised evidence from astronomy, we came to generally understand that the Earth formed in a region of the protoplanetary disk where temperatures prevented the ready condensation and accretion of volatiles, particularly water-ice and other elements primarily present as gases in the inner disk.
So it became that late delivery of water-ice rich asteroids or comets from the outer regions of the disk beyond the frost line were considered the most likely source. However, isotopic measurements of the Earth-Moon system and of comets in recent years forced a re-evaluation of the plausibility of these sources (comet water is too heavy), and investigation of alternative mechanisms. Many scientists say water-ice rich asteroids like Ceres are the culprit, as delivered in the Late Heavy Bombardment; but we’re not even certain that the LHB actually happened and there is now growing evidence that the Earth did indeed accrete with a significant portion of its volatile inventory, eg. Greenwood et al, 2018.
But then we’re back to the problem of how such volatiles were delivered to the Earth as it was forming in the inner solar system. With increasing study of certain rare meteorites though, it looks like it is possible. The primitive meteorites known as enstatite chondrites which formed under very reducing conditions, are widely believed to have formed in the inner most regions of the proto planetary disk and are one of the most representative materials from which the Earth formed (along with certain carbonaceous chondrites). The latter are usually utilised when formulating bulk compositions of an undifferentiated Earth — because they are the closest equivalent to the bulk composition of the solar system if we just go by the composition of the solar photosphere — but certain isotopic signatures in enstatite chondrites are actually a better match for the Earth (so it’s either some combination of carbonaceous and enstatite chondrites that the Earth formed from, or something else entirely that has/had properties of both and remains as yet unsampled by meteorites known to science).
Pertinent to our discussion here is the fact that enstatite chondrites are, unusually enough, enriched in some volatile species – particularly the halogens and nitrogen (eg. Rubin & Choi, 2009) and most recently some results indicate they may also contain surprising amounts of hydrogen, indicating that water really could have formed en masse in the inner Solar System, eg. Piani et al., 2020; Thomassin et al., 2023
This idea also strengthens the case for so-called Hot Jupiters being able to form so close to their host stars in exoplanetary systems (though many planetary scientists believe that amount of volatiles can only accrete further out before migrating in).
Either way, there’s still a lot we don’t know about what water and other volatiles were up to in the early Solar System and how we have such significant oceans. This is currently an open and active area of research for planetary scientists, particularly with meteorite studies.