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Thread: Earth's thermal production

  1. #1 Earth's thermal production 
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    From what I know, the plates such as the tectonic plates are always in motion due to the tremendous amount of pressure created in various areas by the heat in the earth. Energy must be conserved though, so this heat must be lost to the movement of the continents over time, and various other things like volcanoes. This forum came to the conclusion a couple of months ago, regarding my post on earth's entropy, that heat on the surface and in the atmosphere is released through infrared radiation and other forms of EMR-preventing the surface from overheating. The thing is, if this internal heat has been constantly emitted for the past couple of billion years, then why hasn't the earth cooled down already? Various tests have shown that the core needs to remain molten in order to produce a magnetic field; we are not dead is a testament to its continuing retention of heat. Where does it get the heat from? You could say from gravity, or the moon, but that would imply that gravity can naturally give objects heat....which since planets appear to orbit almost forever, would defy the laws of thermodynamics since no energy is being lost form the gravitational field or the rotational velocity. I watched a science channel show on this where someone proposed that the core is actually a nuclear generator that is burning Uranium constantly, allowing it to produce heat. Is this possible? This is more astronomy, but I might as well include it. Certain satellites orbiting Jupiter are extremely hot due to Jupiter's gravity pulling on its surface; how can this be? Jupiter is not loosing any energy.....neither source is converting any of its energy, so how is this possible?


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  3. #2  
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    There have been natural fission reactors in the crust. They require water and (oops, did we do that?) oxygen released by life. We've even mined one spent reactor.

    Deeper (and surely more effective), we have steady radioactive decay. Is it enough?

    Now, you said that "the core needs to remain molten in order to produce a magnetic field" but this is misleading. The deepest part of the Earth appears to be solid or gooily labyrinthine at least because it won't pass vibrations like the rest of our liquid Earth. So we reckon it's (now) cooler than the outer layers, and still cooling. The magnetic field could then owe to convection driven by the boundary of molten and solid. There's your evidence of Earth's cooling.

    I'm unsure why pressure at the center of Earth must be enormous, if net gravity there is zero. ? And what about buoyancy vs. centrifugal force? If you spin a ball of water in orbit, any bubbles in it find their way to the center. ??? Where do heavy metals wind up in this centrifuge?

    Also, why would the Earth cool from the inside-out?


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    Where does it get the heat from?
    A combination of radiative decay, what left over from the planet's accretion, and tidal forcing.

    Various tests have shown that the core needs to remain molten in order to produce a magnetic field
    I think you'd also get a magnetic field from a solid core that's rotating and surrounded by more fluid layers.

    You could say from gravity, or the moon, but that would imply that gravity can naturally give objects heat....which since planets appear to orbit almost forever, would defy the laws of thermodynamics since no energy is being lost form the gravitational field or the rotational velocity.
    Energy is being transferred and lost both to the sun and moon. Specifically the earth is slowing rotation and transferring that momentum to the moon which is slowly increasing its distance from the planet--obviously some of that is being lost as heat.
    --
    I'm unsure why pressure at the center of Earth must be enormous, if net gravity there is zero.
    The pressure comes from the accumulated weight above.
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    Quote Originally Posted by Pong
    There have been natural fission reactors in the crust. They require water and (oops, did we do that?) oxygen released by life.
    http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor
    The water acts as a moderator. Oxygen may have facilitated the solution and subsequent deposition of uranium in concentrations high enough to generate a self sustaining nuclear reaction.

    Nuclear reactions within the core would be different in mechanism:
    http://www.pnas.org/cgi/reprint/98/20/11085.pdf

    Deeper (and surely more effective), we have steady radioactive decay. Is it enough?
    Yes. The current consensus is very much that it is enough.

    The deepest part of the Earth appears to be solid or gooily labyrinthine at least because it won't pass vibrations like the rest of our liquid Earth.
    There are several things wrong with this.
    There is nothing to suggest the inner core is in any way gooey or labyrinthine.
    The rest of the Earth is not liquid. The outer core is liquid. the mantle crust and inner core are solid. small portions of the mantle, especially the upper mantle may undergo partial melting.
    The inner core will pass all seismic vibrations it experiences, just like any other solid parts of the Earth. It is the liquid outer core that does not pass S waves, but only P waves.
    So we reckon it's (now) cooler than the outer layers, and still cooling
    Yes, it is still cooling, but it is not cooler than the outer layers. Where did you pick up such a strange idea? Temperature increases as we go down. The rate of change will vary with composition and density, and be influenced by convection currents in the mantle and the outer core. But the general trend is an increase. Full stop. Period.

    I'm unsure why pressure at the center of Earth must be enormous, if net gravity there is zero.
    Because the pressure is determined by the sum of the incremental forces generated by the mass of the material above that point.
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    Maybe they only meant to apply the idea to small bodies of metal......the test tried to determine the differences between a solid mercury sphere, and a liquid one. The liquid gave off considerably higher levels of magnetic and even gravitational energy. Still not allot, but allot in comparison to solid pieces of metal.

    That really is amazing, that nuclear fission reactions could naturally occur in the earth.

    As a solution to the core cooling down (supposedly reducing the magnetic field considerably, and the gravitational field slightly), someone suggested "melting a hole" to the center of the earth, a dropping enriched Uranium in. Is this at all feasible?
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

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    You're right Ophiolite, the core is ...er, freezing... because the entire Earth is cooling, yet pressure hasn't changed. There is a contest between, on one hand, heat keeping the iron liquid; and on the other, compression working to solidify it. Each value must be enormous to match the other, and one is gradually diminishing.

    "Gooey or labyrinthine" are just possible explanations for the apparently irregular shape of our core. It's not mapping well, as a nice smooth ball should. It seems to vary in thickness. It seems to have fine scale surface features. It's frustrating our best efforts to get a clear picture!

    My guess is that our core is as roughly spherical as a well-crafted snowball, perhaps echoing our over/under tectonic plates; often deeply cracked by uneven contraction of the iron (see this in foundries); and lacily irregular at the boundary, which fades from solid, to plastic, to liquid. Hey, maybe it has a bit of spiral arm action like a galaxy? Picture solar flares and lavalamps, at glacial speed. Well, we could just draw a circle and assume some part of this Earth so simple. :?
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    Quote Originally Posted by Cold Fusion
    As a solution to the core cooling down (supposedly reducing the magnetic field considerably, and the gravitational field slightly), someone suggested "melting a hole" to the center of the earth, a dropping enriched Uranium in. Is this at all feasible?
    1. Why would a cooler core reduce the gravitational field? Cooler does not mean less mass.
    2. The uranium plug concept is plausible, but technologically impractical.
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    The uranium sinks, doesn't it? But it begins to run into convection currents... diverge... and... at some depth, there just isn't much "heavier" because gravity is not a point at Earth's center.

    There's evidence that the core spins slightly relative to Earth, one way or another. In that case the dense uranium could be thrown outward.

    Quote Originally Posted by Pong
    Where do heavy metals wind up in this centrifuge?
    Core orbit, anyone? And yeah, centrifuge.

    ???
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    for some reason or another the concentration of uranium is higher than you would expect from such a heavy element, if i remember correctly due to an affinity to combine with the abundant silicates in the crust
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  11. #10  
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    Quote Originally Posted by Pong
    The uranium sinks, doesn't it? But it begins to run into convection currents... diverge... and... at some depth, there just isn't much "heavier" because gravity is not a point at Earth's center.
    This makes no sense to me: semantically, syntactically, or scientifically. Can you clarify?
    Quote Originally Posted by Pong
    There's evidence that the core spins slightly relative to Earth, one way or another. In that case the dense uranium could be thrown outward.
    No it wouldn't. Firstly, the difference in spin rate is minimal. Secondly, the difference in spin rate is irrelevant to the centrifugal force generated. Thirdly, the centrifugal force is an order of magnitude or more, less than the gravitational force.
    Quote Originally Posted by Pong
    Quote Originally Posted by Pong
    Where do heavy metals wind up in this centrifuge?
    Core orbit, anyone? And yeah, centrifuge.
    ???
    As noted, the centrifugal effect is minimal. It didn't overcome the gravity stratification of the planet when it formed within the solar accretion disc. It isn't going to suddenly (or slowly) reverse those trends now. Why do you think it would?
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  12. #11  
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    Quote Originally Posted by Ophiolite
    Quote Originally Posted by Pong
    The uranium sinks, doesn't it? But it begins to run into convection currents... diverge... and... at some depth, there just isn't much "heavier" because gravity is not a point at Earth's center.
    This makes no sense to me: semantically, syntactically, or scientifically. Can you clarify?
    Q: What is the weight of 1kg uranium near the Earth's center?
    A: "Minimal", to borrow your word.

    I'm interested in how all these factors varying with depth might promote layers, dynamics, or even structures.
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  13. #12  
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    Quote Originally Posted by Pong
    Quote Originally Posted by Ophiolite
    Quote Originally Posted by Pong
    The uranium sinks, doesn't it? But it begins to run into convection currents... diverge... and... at some depth, there just isn't much "heavier" because gravity is not a point at Earth's center.
    This makes no sense to me: semantically, syntactically, or scientifically. Can you clarify?
    Q: What is the weight of 1kg uranium near the Earth's center?
    A: "Minimal", to borrow your word.
    It is still denser than material it would be denser than at the surface by the same ratio.
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  14. #13  
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    Yes. The weights of iron and uranium approach equilibrium, but the densities don't. What happens when you spin materials of varying density in a bowl - kinda analogous to our ...er, inverted gravity well?
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    And just because it's fun to think about, the center of the earth isn't the center of gravity. The center of gravity is an ever shifting balance between the earth, moon and sun.
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    Tide must be working on inner Earth, I hadn't thought of that.

    But if the core is moved by tide, wouldn't Earth's path be slightly wobbly, inexplicable by other factors? Heh. This is just like testing if an egg is boiled by spinning it.
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  17. #16  
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    Quote Originally Posted by Pong
    Yes. The weights of iron and uranium approach equilibrium, but the densities don't. What happens when you spin materials of varying density in a bowl - kinda analogous to our ...er, inverted gravity well?
    Relative values Pong. Are you reading anything I have written?
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  18. #17  
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    Yes I'm reading with interest, thanks, though I'm unsure what you're trying to say. I'm speculating about what happens to inner-Earth uranium.

    What do you think happens to it?
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  19. #18  
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    Quote Originally Posted by Pong
    What do you think happens to it?
    It is a lithophile element. It 'likes' to combine with elements that form minerals that are commonplace in the crust and mantle. It is not a siderophile element. It does not 'like' to combine with iron.
    Therefore I lean strongly to the consensus view that the bulk of the uranium is to be found in the crust and the mantle. I do not rule out the hypothesis (discussed in the paper I referenced earlier) that a significant amount of uranium made its way to the core, but I think this is the less likely possibility.

    You keep referring to centrifugal effects. Certainly these are sufficient to produce a noticeable equatorial bulge in the Earth, but they are not enought to 'throw' the denser elements to the outside. The gravitational forces far exceed these centrifugal effects. The denser material will tend to sink towards the centre of the Earth, though this tendency can be overriden by chemical attractions.
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  20. #19  
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    Quote Originally Posted by Ophiolite
    I lean strongly to the consensus view that the bulk of the uranium is to be found in the crust and the mantle. I do not rule out the hypothesis (discussed in the paper I referenced earlier) that a significant amount of uranium made its way to the core, but I think this is the less likely possibility.
    Lean strongly? What does that mean? Since when did I claim "the bulk of uranium", or even a "significant amount"? You seem to be saying that, because most water is found in oceans, it is pointless to speculate about the possibility of clouds.
    Quote Originally Posted by Ophiolite
    ...centrifugal effects... are not enought to 'throw' the denser elements to the outside.
    Strawman. Please don't throw a discus when we're talking about very gradual creeping, as in a glacier. Again, your position seems on par with discounting the moon's tide because the Earth's gravity is so much greater.
    Quote Originally Posted by Ophiolite
    The gravitational forces far exceed these centrifugal effects.
    Does that simply negate them?

    *sigh*

    I would speculate that the core has an equatorial bulge, but I can sense the dismissive reflex of Ophiolite already. The proposition that uranium could settle in layers or patterns is going nowhere either.

    OK, now it's my turn. :P
    Quote Originally Posted by Ophiolite
    denser material will tend to sink towards the centre of the Earth, though this tendency can be overriden by chemical attractions
    This overriding chemical attraction is worth mention in the context of uranium settling through molten convection currents? Illustrate..?
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