An iron rain fell on Earth early in its formation


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New research attempting to explain why the Earth but not the Moon has so much iron splattered through its mantle has found that iron can be more easily vaporized during impacts than previously thought, and thus rained down on the planet during the early asteroid bombardment.

Principal investigator Kraus said, “Because planetary scientists always thought it was difficult to vaporize iron, they never thought of vaporization as an important process during the formation of the Earth and its core. But with our experiments, we showed that it’s very easy to impact-vaporize iron.” He continued, “This changes the way we think of planet formation, in that instead of core formation occurring by iron sinking down to the growing Earth’s core in large blobs (technically called diapirs), that iron was vaporized, spread out in a plume over the surface of the Earth and rained out as small droplets. The small iron droplets mixed easily with the mantle, which changes our interpretation of the geochemical data we use to date the timing of Earth’s core formation.”

The Moon’s gravity in turn wasn’t sufficient to pull its own iron vapor down. Thus, it does not have much iron in its mantle.

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3 comments

  • mpthompson

    I thought the lack of iron in the Moon’s mantle and core was explained by the Moon primarily being composed of material from Earth’s mantle and crust being thrown into orbit from a collision with a Mars size planetiod just as the late bombardment was ending. After that collision the Earth nor the Moon would have acquired appreciable more iron from other collisions as bombardment was largely over.

    The Moon is basically made from second hand material already deficient in iron. The similarity of the Moon’s interior including its core being similar in composition to Earth’s crust and mantle being evidence for this particular model of the Moon’s formation.

    These investigators seem to be suggesting an alternate model of the Moon’s formation different from the generally accepted model — a model where they expect the Moon to have significantly more iron than the collision model already accounts for.

  • PeterF

    The “iron rain” theory would suggest that planets similar to the earth should be fairly common and therefore the probability of life forms similar to ours should be fairly common. The “Star Trek” universe is just a matter of time…

    The “collision” theory would suggest a precise and rare event formed the earth and therefore we may be unique in the galaxy. I hope our descendants don’t get lonely…

  • mpthompson

    You presume that the Moon is important, if not critical, to the development of terrestrial life. If seen books that atempt to present such an argument, but I’m not sold. Certainly the Moon has shaped evolution to varying degrees, but this is a far cry from saying that sophisticated life forims are not possible without a collision that formed the Moon.

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