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Did the core of the Earth collide with the Earth billions of years ago?

  1. Feb 22, 2007 #1
    Does the core of the Earth belong to the Earth or did it come from outer space and collide with the Earth.In this scenario the volume of the moon added to the volume of the continental rocks should equal the volume of the
    core ( the collision would have displaced material from inside the Earth).And could such a collision have fractured the Earth's surface starting plate tectonics?
  2. jcsd
  3. Feb 22, 2007 #2


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    ALL of the mass of the earth came from "outer space".
  4. Feb 22, 2007 #3


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    I'm not too familiar with the theory of collision of a large body with the early earth, but I thought that the theory went that the earth was pretty much melted, rather than fractured. Plate fracturing doesn't seem to need any impact to start it off today, so I doubt that it would be nessecary on the early crust, which was most likely quite a bit thinner.
  5. Feb 22, 2007 #4
    The collision would have had to have been at a precise angle or else the extra momentum imparted to the Earth would have made it leave the solar system or go into the Sun.This makes a collision on this scale seem unlikely in itself.
    Last edited: Feb 22, 2007
  6. Feb 22, 2007 #5
    Well I think it would probably be agreed that some of the core came from early impacts, if you're suggesting that we were hit by a large ball of iron that eventually found its way down to the centre of the earth then no, that didn't happen.

    A large impact would have melted (some of) the earth by the mechanism of decompressional melting, caused by a phase of decompression immediately following the impact. It is actually thought that this would cause a plume in the upper mantle, perhaps somehow this helped get plate tectonics going?
  7. Feb 22, 2007 #6
    Any large collision that an iron core could have had with the Earth to cause the moon to form would have had to have taken place more than 3 billion years ago (water has been on Earth for 3 billion years) or else we would expect there to be a lot of water removed from the Earth on the moon and floating around in the path of Earth's orbit as blocks of ice.There is not and the core is only 2.5 billion years old.Also there is the unlikeliness of a precise angle of attack by a large projectile (to stop the Earth going out of orbit of the sun),so I suspect the Earth and moon formed side by side in space.
    Last edited: Feb 22, 2007
  8. Feb 26, 2007 #7
    Further evidence against a core colliding with Earth is that we would expect
    water to have been ejected from the oceans into space,and this would mean that the ratio of deuterium/ normal hydrogen would be bigger in the sea than is
    observed (deuterium is heavier than normal hydrogen and so less water containing it would get the velocity required to escape from the Earth).
    Last edited: Feb 26, 2007
  9. Feb 27, 2007 #8
    Or it might have collected on the moon, in fact there are people who believe that the record of some of earth's larger impacts might be preserved on the moon (which itself is generally thought to be the record of a very large impact), this is an interesting prospect indeed as a lot of the evidence on our own planet of past impacting events has been lost by resurfacing processes.

    Is it? I didn't know that, can you please back that statement up.

    The energy from the moon forming impact is thought to have been converted into the angular momentum that the earth moon sytem has as a whole as well as providing energy for the earth's rotation -which is why we have days!! Again, this statement seems rather bold, did you come up with that off the top of your head or have you seen some kind of study which comes to this conclusion.

    Again I didn't know that, have you got a reference?
  10. Mar 8, 2007 #9
    The amount of energy needed to lift the Earth out of the solar system would have vaporized both objects. And to direct the Earth into the sun, the impact would have to be at a precise angle. I would have expected a major collision to result in a strongly elliptical orbit.

    I get your point though, that we might expect a major collision to alter the orbit in some dramatic way. But astronomers do think the moon was formed by collision. I don't understand the mechanics either. I know our orbit is slightly elliptical, but not by much.

    Here are my first 4 hits on a Google search for "formation of the moon"

  11. Mar 13, 2007 #10
    Our orbit was altered in a dramatic way, we now orbit the moon as well as the Sun.
  12. Mar 13, 2007 #11
    That's a great answer Mr B! It ducks the question though I think. Or maybe not. I guess what I'm really talking about is the orbit of the Earth-moon pair as the resultant momentum vector of the collision. Doesn't it have to be radically different from the pre-collision vector of the Earth alone? Not that we would know what that was, but I still don't get why the orbit is so well behaved.

    I know I'm missing something and I suspect it has to do with rotational momentum . . . ? Or maybe the momentum of the orbiting Earth is so great that the impact had less effect than I imagine.
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