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Earth's core, solid or not?

  1. Feb 9, 2013 #1
    Hi Guys,

    This may seem like a stupid question but if the Earth gets hotter the closer to the core you get, then why is the inner core apparently solid? Yet the outer core is liquid?

    They are both (inner/outer cores) made of roughtly the same stuff, and assuming pressure alone is what heats the core, why would it be cool enough to solidify in the centre?

  2. jcsd
  3. Feb 9, 2013 #2


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    It doesn't have to be cool to solidify. Increased pressure can solidify liquids as well, especially if the solid has lower volume than the liquid.

    Pressure doesn't heat the core, no idea what you mean by that.
  4. Feb 9, 2013 #3
    Hi Borek,

    Thanks for your reply.

    Firstly then, what causes the heating?

    Secondly, I don't fully understand why the core should be solid. If the core has less mass and the same amount of heat around it, then shouldn't the core change phase more easily?

    The only way I can see the effect happening is if the Earth is heated from an external source and the heat doesn't radiate(/conduct/convect) well enough to melt the core.

    Much like frying some butter in a frying pan. The frying pan is external to the butter, and as the pan heats up, it heats the external surface of the butter, whilst the core of the butter is still solid (for a while).
  5. Feb 9, 2013 #4


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    There are two sources of heating - radioactivity and tidal forces.

    The deeper you go, the higher the pressure and the temperature - it happens that as some depth PT are such that the melt solidifies.
  6. Feb 9, 2013 #5
    Oh ok.

    So why would radioactivity be higher as you get deeper? Has anyone done any sort of mining to show this to be the case?

    What would induce the core tidal forces? I know the Moon is supposed to control the surface ocean waves.

    you mention:
    What experimental evidence has been gained sofar to profile the Earth's PT to the core? Do you have any links I can read about?

    I suppose you're wondering where I'm taking this? Well, some of the data I've found suggests the core heating and rotation may be of electromagnetic origin. However before I put the whole idea out for sanity checking, I need to make sure the pieces of the puzzle fit together. Theidea seems scalable too, which points to other practical implications.
  7. Feb 9, 2013 #6


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    Gravity: radioactive isotopes are heavy.
    We are not capable of mining that deep.
    This forum allows neither crackpottery or unpublished personal theories.
  8. Feb 9, 2013 #7


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    The Kola Superdeep Borehole is the deepest anyone has ever drilled into the Earth's surface. It reached 12,262 metres underground, which was about 1/3 of the way through the crust.

  9. Feb 9, 2013 #8


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    It is not. That is, as the elemental composition is not constant, for sure there exist some stratification, but there is no need for the radioactivity to get higher when you get deeper to explain the temperature differences.

    Tidal forces don't act on water only, they deform the whole planet.
  10. Feb 9, 2013 #9


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