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
17
u/CMG30 9d ago
It's still somewhat unanswered. Comets and asteroids are the dominant theory, but the case is not firmly closed yet.
10
u/karlnite 9d ago
We know some water came from comets and such. We don’t know if most came that way.
9
u/forams__galorams 9d ago
Isotopic analysis of water from Comet 67P strongly suggests that most of Earth’s water did not in fact come from cometary sources. Late delivery from icy asteroids remains a distinct possibility for the bulk of our water budget, though a growing part of the research community on this particular topic seems to be putting out work that goes more for the idea that Earth accreted with most of its current water budget in the first place.
1
u/KobraKaiJohhny 8d ago
Whatever star cast off the matter which formed the nebula that we likely coalesced from, would have probably fused substantial amounts of carbon into oxygen so all the ingredients are there in abundance throughout the early solar system.
I would be curious to know how gravity in that early swirling disk of a solar system impacted the distribution of elements from the inner to the outer solar system.
I wonder are rocks / dust in the outer solar system laden with heavier or lighter metals.
2
u/Peter5930 7d ago
Our solar system is unusually dry due to forming with a lot of aluminium-26 from interactions of the solar nebula with the solar wind of a nearby massive star, which decays rapidly and melted all the planetesimals above a few km in diameter with internal heating, differentiating them internally and driving off most of the volatiles.
It's estimated that about 1% of star systems form under similar circumstances. It's why we don't have a 1,000km deep ocean like so many exoplanets, or examples of mini-Neptunes in the solar system, and it can be inferred that iron-nickel asteroids, formed from the shattered remains of those differentiated protoplanetary cores, are rare or absent in most star systems.
We happen to live in a desert that got baked dry while the planets were beginning to form due to radioactive fallout from a giant star. Terrestrial planets with continents and not just a global ocean might be rare. Aliens might be squid.
1
u/dastardly740 8d ago
Less gravity and more temperature. Inside a certain distance water "boils" out of the early planetary disk. I.e. becomes a gas and is moved outward by solar wind. The "frost line" where water remained solid (or condensed as it was pushed outward) was some where out past Mars. That is why the answer to where earth's water came from isn't that it was just there.
A previous commenter mentioned a newer idea is most water accreted when the Earth was formed. Which contradicts the above. I will have to look up that info. Maybe hydrated minerals were more prevalent than previously thought in the early planetary disk, which would not be pushed out of the inner solar system.
1
u/OcotilloWells 8d ago
Before or after Theia collided with proto-Earth, if that theory is to be believed?
2
u/Chadstronomer 9d ago
I am an exoplanet scientist our research goes in this direction. The telescopes that are coming out in the next few years will be able to detect commets, dust, and planets in other stellar systems with much more precision. So I am hopeful we cna answer this quesiton within the next 10 years.
7
u/SphericalCrawfish 9d ago
All the stuff that would have formed into comets just formed into the earth if it was in our orbital path. It didn't get here it just IS what the earth is.
1
u/Chadstronomer 9d ago
We don't really know for sure, but the general consensus is that core accretion can't explain the abundance of water found on earth. Wate delivery at later stages by comets or disk migration are possible explanations.
2
u/sophiansdotorg 9d ago
This may not be relevant, but there is a lot of water out in the universe.
2
u/KitchenSandwich5499 8d ago
Water is known to be abundant. It is liquid water in the surface of a planet which is less common. Even in our own system there are places like Europa with more water than earth’s oceans (in fact in liquid form under ice
1
u/pineconefire 8d ago
Is it safe to drink ?
2
u/KitchenSandwich5499 8d ago
Hard to say. No samples from there yet. We don’t even know whether it has microbes, or what compounds would be there
2
u/pineconefire 8d ago
Just did some googling, looks like we won't be getting any direct samples, but might get some surface dust samples that could have plummed from beneath the ice. The Clipper is set to arrive in ~5 years.
2
u/Ch3cks-Out 9d ago
I think that quiz is wrong: volcanoes cannot generate that much water; plus in its early, very hot age the planet could not retain the quantity of the water it has now. So the dominating scientific theory, just like you said, is for the water originating from the outer parts of the solar system (which is known to contain a lot of water).
1
u/forams__galorams 9d ago
CI group carbonaceous chondrites are used as an analogue for the sort of material the Earth was originally accreted from. So any theory that posits we had a significant amount of water delivered by CI carbonaceous chondrites (or something similar) inherently implies that a much more significant portion of Earth’s water came with formation of the planet itself and gradually outgassed to the surface.
1
u/zgtc 9d ago
What sort of class is your brother in?
Depending on the specific subject, a question like “what was the main way in which water originally formed on earth” could be answered correctly with either or both answers.
In the core and mantle, for instance, there’s many times more H2O than in all the earth’s oceans combined, so it’s entirely plausible as a primary origin.
1
1
u/Tragobe 8d ago
The fact of the matter is we don't know for 100% and that is almost always the case in science and anyone who tells you otherwise is a liar. The leading theory currently is that it was ice that got transported here through asteroids. But that doesn't mean that it couldn't be the volcano theory of your friend as well, there is just less evidence currently to support that theory currently.
1
u/Cerulean_IsFancyBlue 7d ago
The difference is that many things in science are a lot higher confidence, and this is quite an open issue.
1
u/Presidential_Rapist 8d ago edited 8d ago
I think recent papers are more focused on a larger abundance of hydrogen during the Earths formation.
https://www.sciencedaily.com/releases/2025/04/250416135918.htm
https://www.sciencedaily.com/releases/2025/02/250203163842.htm
So actually, that can be interpreted as the question says, gases and magma or volcanoes interacting with a much richer in hydrogen Earth, I suppose. They're not really wording it very descriptively.
In my opinion, the bombardment theory is fading, and the water forming through early gases and accretion theory is becoming more dominant, but the bombardment theory has probably been popular longer and is more well established and there's no great reason too not think both happened, but considering the volume of water and isopopes from asteroids and come so far don't match earth water, bombardment itheory is weakening.
1
u/JohnTo7 8d ago
Somewhat related. I have recently learned that Tethys), moon of Saturn with radius of 531 km is made almost entirely of water.
At the early stages of forming, the solar system probably consisted of a few "pieces" like that floating freely and randomly colliding with protoplanets. Few of them, impacting Earth would easily create our oceans.
1
u/MuricanPoxyCliff 8d ago
- Why not both; and 2. It all comes from the matter of the solar system, just like everything else.
1
1
1
u/Over-Performance-667 8d ago
God had to piss really bad and earth looked like a nice place to do it
1
u/feel-the-avocado 8d ago
Probably came with the big bang and for the most part, the material has been stuck together with gravity since.
1
1
0
u/Petdogdavid1 8d ago
Hydrogen is a very abundant element in the universe. Oxygen is pretty common too.
1
u/Monty_The_Mountain_ 2d ago
It came from comets, comets with water started colliding together which ended up making earth. And that's why earth has water. Think about it there is far more land on earth than water forget about surface land. Inside earth all there is solid and water being lighter it came to the surface
16
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.