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Does the earth expand and contract

  1. Jul 31, 2007 #1
    perhaps some of the crust structure texture (mountains & canyons) is constructed from the earth expanding and contracting like a balloon does when it warms or cools, though I'd think this would all be based on its internal temp...

    Dan
     
    Last edited: Jul 31, 2007
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  3. Jul 31, 2007 #2

    matthyaouw

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    You should read this introduction to plate tectonics (split across several pages).

    The important point to take from reading that is to learn that crust is created and destroyed in balance- if crust is destroyed or compresed in one area then to balance this there is more created at the mid ocean ridges. Mountain building (aka orogeny) happens when tectonic plates collide as shown here. This is largely due to physical stress rather than thermal changes. Most valleys and canyons are formed by erosion, but rift valleys can be formed when crust spreads locally and forms faults, leading to graben formation. Again this is largely due to physical stress rather than temperature.
    The earth is slowly cooling and thus shrinking but this rate is miniscule and insignificant compared to plate tectonic processes. I wouldn't be surprised if the rate at which it shrinks is overbalanced by the rate at which it recives material from space leading to an overall growth.
     
  4. Aug 2, 2007 #3

    LURCH

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    Nevertheless, it is an interesting question. Does the interior temperature fluctuate? And if so, does the globe expand or contract, and could this veriable any apreciable amount of buckling of the crust. Obviously, any such effect would be very small, but could it eb measured?
     
  5. Aug 2, 2007 #4

    matthyaouw

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    Earth has no internal heat source that I'm aware of so I'm not sure it could increase in temperature. Tectonic activity and configuration/size/thickness of plates could affect the rate of cooling on a global scale, but I'd think only on incredibly long timescales.

    Local differences on the other hand... The majority of scientists think that hot spot swells are at least partially due to local heating of the earth's crust by hot buoyant mantle plumes.
     
  6. Aug 2, 2007 #5

    mgb_phys

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    There are intenrla heat sources from radioactive decay and tidal friction from the moon - but neither are enough to seriously change the temperature of the core.
    There is a significant amount of up or down motion of the crust at northern latitiudes as it 'rebounds' from the weight of the ice being removed in the last ice-age. This is in the mm/year range for parts of northern europe.
     
  7. Aug 3, 2007 #6

    LURCH

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    Now here's something I would like to get straitened out in my head; I thought I once heard that the internal sources, and especially radioactive decay, are by far the dominant heat source of the interior, and that the heat from the planet's original formation would have cooled off much more by now than it has, if it weren't for this heat source. Is this incorrect?
    Also, good point about the hotspots like Hawaii, Mathyaouw. These of course represent a change that is dependant on location rather than time, but they illustrate the idea that an internal temperature change can have a quite significant effect on surface topography.
     
  8. Aug 3, 2007 #7

    mgb_phys

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    The core was melted by radioactive decay shortly after the earth formed.
    The current molten core is molten because it hasn't cooled down yet. The cooling rate is very low because there is quite a lot of it and the crust isn't a good conductor.
    I don't know what the current heat input from radioactive decay is, probably low since it will only be from remaining long-lived low-activity species.
     
  9. Aug 5, 2007 #8

    LURCH

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    About two-thirds down the page at this site:
    http://www.agu.org/meetings/fm06/fm06-sessions/fm06_MR53A.html
    it says
    But it doesn't say how important. Of course, the paper ends with a proposal to build an antinutrino detector to try to measure just how much radiation is involved.
     
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