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Earth Science

Water on Earth May Not Have Originated from an Asteroid Impact, Study Finds (discovermagazine.com) 29

Posted by EditorDavid from the water-everywhere dept.
Discover magazine reports that a team of researchers have produced evidence that the ancient building blocks for water have been here on earth "since early in the planet's history, according to a study published in the journal Icarus." Pinpointing when and where Earth's hydrogen [originated] is an essential key to understanding how life arose on the planet. Without hydrogen, there's no water, and without water, life can't exist here. Ironically, researchers turned to a meteorite containing hydrogen to prove that such former bodies did not provide the H2 ingredient of water's H2O recipe. They examined a rare type of meteorite — known as an enstatite chondrite — that was built similarly to early Earth 4.5 billion years ago and the team discovered hydrogen present in the chemical. The logic is that if this material resembling early Earth's composition can contain hydrogen, so too could the young planet....

Since the proto-Earth was made of material similar to enstatite chondrites, by the time the immature planet had grown large enough to be struck by asteroids, it would have already stashed enough hydrogen to explain Earth's present-day water supply.Although this study likely won't resolve the debate over Earth's original water source, it tilts the ta ble toward an internal, not external one. "We now think that the material that built our planet — which we can study using these rare meteorites — was far richer in hydrogen than we thought previously," James Bryson, an Oxford professor and an author of the paper, said in a press release. "This finding supports the idea that the formation of water on Earth was a natural process, rather than a fluke of hydrated asteroids bombarding our planet after it formed."

Water on Earth May Not Have Originated from an Asteroid Impact, Study Finds More | Reply

Water on Earth May Not Have Originated from an Asteroid Impact, Study Finds

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  • My 2 cents on this one. (Score:5, Interesting)

    by zurkeyon ( 1546501 ) on Sunday April 20, 2025 @10:56AM (#65318721)
    When viewing simulation of planetary formation, many times, there is a vast accretion disk around the planet for some time. Especially in massive body collision simulations. The one that Created the moon for example, would have left the crust molten for 50,000-200,000 years. That water would have had to have been in gas form, (an Entire Global set of Oceans worth.) for all of that time. I cannot see that much water floating around as clouds. It makes more sense that it was in the accretion disk after the initial collision, trapped by the combined gravity of both bodies unified, and eventually "Rained down" s n atmosphere formed from the remains of the accretion disk. Would have taken a few million years for that to happen. Plenty of time for the newly formed "Earth" to have solidified a surface, and cooled enough to support oceans/basins.

    • Re: (Score:3)

      by evanh ( 627108 )

      I see the model inverted. The water is deep in the centre from the outset. It takes a long time for the water to escape to the surface. Just like it takes a long time for heat to also escape.

      • I see the model inverted. The water is deep in the centre from the outset. It takes a long time for the water to escape to the surface. Just like it takes a long time for heat to also escape.

        Not at all unreasonable; several geophysicists have suggested that the Earth has a lot of deep water bonded to the mantle rocks; and possibly more water deep than there is on the surface.

        Do keep in mind that the Earth is quite well differentiated, so unless the water is dissolved in the mineral at equilibrium concentration for the pressure and temperature, it will have differentiated out (which, because it's so low density, means to the surface).

    • H2S [Re:My 2 cents on this one.] (Score:4, Informative)

      by XXongo ( 3986865 ) on Sunday April 20, 2025 @12:35PM (#65318863) Homepage

      When viewing simulation of planetary formation, many times, there is a vast accretion disk around the planet for some time. Especially in massive body collision simulations. The one that Created the moon for example, would have left the crust molten for 50,000-200,000 years. That water would have had to have been in gas form, (an Entire Global set of Oceans worth.) for all of that time. I cannot see that much water floating around as clouds.

      The suggestion here was the hydrogen was not in the form of water, H2O, but in the form of hydrogen sulfide, H2S. Which is also a gas, but the hypothesis here is that the H2S is dissolved in the molten silicate of the accretion disk. https://doi.org/10.1016/j.icar... [doi.org]

      Not mentioned in the abstract is how this leads to water (*), but presumably after the Earth cools a bit, the H2S outgasses from the silicate rock (possibly as volcanic or thermal vent emissions) and reacts H2S + O2 --> H2O + SO
      (and the SO then goes on to oxidize further into sulfate).

  • Due to their isotopic similarity to terrestrial rocks across a range of elements, the meteorite group that is thought to best represent Earth's building blocks is the enstatite chondrites (ECs)... Here, we explore the amount of hydrogen in ECs as well as the phase that may carry this element using sulfur X-ray absorption near edge structure (S-XANES) spectroscopy. We find that hydrogen bonded to sulfur is prevalent throughout the meteorite, with fine matrix containing on average almost 10 times more H-S tha

    • Re: (Score:2)

      by XXongo ( 3986865 )

      ...We find that hydrogen bonded to sulfur is prevalent throughout the meteorite, ...
      sulfide can sacrificially catalyse a reaction with H2 from the disk at high temperatures to create H2S, which could be dissolved in adjoining molten silicate-rich material...

      The conclusion of this is that for every two molecules of hydrogen there must be one molecule of sulfur. Since sulfur is 32 times heavier than hydrogen, that means sulfur in the Earth's composition outweighs hydrogen by a factor of 16 to 1.

  • For many years I have heard about the prevailing theory about how the Earth's oceans accumulated due to the impact of water-heavy comets. What I never understood was why comets would have so much water in them where the material that made up the Earth did not.

    Can someone explain how the theory covers this?

    • There is only one way - multiple hits. Many thousands of multiple hits, in fact, as water on Earth is about 2x10^9 cubic km, the largest comet ever seen was more than 3 orders of magnitude smaller and Earth could not have retained all water from all the hits.

    • For many years I have heard about the prevailing theory about how the Earth's oceans accumulated due to the impact of water-heavy comets. What I never understood was why comets would have so much water in them where the material that made up the Earth did not. Can someone explain how the theory covers this?

      Comets form in the far outer solar system, well beyond the "frost line", the distance at which water is a rock, not a liquid or gas. The comets are then scattered into the inner solar system by perturbations from the planetary gravity (keeping in mind that in the earlier solar system, planets had not yet settled down into the nice stable orbits they now have).

    • What I never understood was why comets would have so much water in them where the material that made up the Earth did not.

      IIRC, they thought that the material was close enough to the sun to boil off the water before the earth formed, or the earth was hot enough early on to eject the hydrogen it had. Thus the need for comets from cooler regions to replenish the water later on.

  • It's pretty obvious looking at how much water ice is floating in space that it's a highly common resource in the early formation of planets generally. There's probably more water than rock if comets and planetary rings are any measure.

    If it's buried deep inside from the outset then there's plenty to go round. I wouldn't be surprised if there is still plenty of superheated water buried deep in the Earth.

  • https://en.wikipedia.org/wiki/... [wikipedia.org]

    Enstatite chondrites (E-type chondrites) are a rare form of meteorite, rich in the mineral enstatite.

    https://en.wikipedia.org/wiki/... [wikipedia.org]

    Enstatite is a mineral; the magnesium endmember of the pyroxene silicate mineral series enstatite (MgSiO3) – ferrosilite (FeSiO3). The magnesium rich members of the solid solution series are common rock-forming minerals found in igneous and metamorphic rocks. The intermediate composition, (Mg,Fe)SiO3, has historically been known as hypersthene, although this name has been formally abandoned and replaced by orthopyroxene. When determined petrographically or chemically the composition is given as relative proportions of enstatite (En) and ferrosilite (Fs) (e.g., En80Fs20).

    My thought is that it wouldn't have to actually hit "Earth" per say since at one point "Earth" was an protoplanetary disk. Basically, if lots of small enstatite chondrites impacted part of the asteroid ring, then a certain amount would statistical remain in the ring instead of passing through. It could even have impacted the outer protoplanetary disk and slowed enough to get pulled back near Earth's disk. It wouldn't need to be all at once

  • Different mindsets point to the same conclusion.

    We can look at this geologically - check the pegmatites formed on earth. We have a few types, but one distinguishing feature tends to be WATER CONTENT. The quartz that is formed is HYDROTHERMAL in nature, and there are micro fluid inclusions that record the conditions that formed the pegmatite, and in those fluid inclusions can be micro crystals of deep magma minerals. Thus, this water was already deep inside the mantle, it is very likely that it had to be the

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