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Radioactive material as it relates to Earth

  1. Mar 10, 2004 #1
    How long does radiactive material remain radioactive.?

    I ask this in light of the issue of earth's core heating.

    It seems to me the radioactivity model has to explain how such material remains seemingly radioactive to this day. 4.5 billion years after the earth was formed.

    Does that defy what we know of material such a uranium etc all of which lose radiactivity over a relatively short period of time compared to the Earth's entire geological history. ?

    Or am I mistaken in my understanding of these things ?

  2. jcsd
  3. Mar 11, 2004 #2
    Good questions Aquafire.

    We can explain things for hours talk about Uranium Thorium series, Kalium Argon series, the thermo geo nucleair reactor but in the end the answer is: we don't know we can just speculate. Do you want a higher level of ignorance?
  4. Mar 12, 2004 #3


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    Kalium = Potassium :P

    What I could find on the net is that the isotope with the longest known half-life is tellur-128 (1.5 E24 years) and with the shortest is radium-216m (7E-9 s = 7 ns). Don't ask me how it is related to the Earth model though :) it just demonstrates the limits.
  5. Mar 12, 2004 #4


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    About elements with a very long half-life.. this is interesting to consider:

  6. Mar 18, 2004 #5


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    A quick goole will tell you the half life of any element (isotope). Have a look at THIS
    So over the age of the Earth, roughly half of all the U238 that existed at the earth's formation has decayed.
  7. Mar 19, 2004 #6


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    AFAIK, the most important elements/isotopes - re heating the Earth - are uranium, thorium and potassium-40. Why? A combination of abundance and long half-life.

    Did you know there was once a natural reactor right near the surface of the Earth?
  8. Apr 2, 2004 #7
    We have had a long discussion of the heating of the earth core here

    I suggested that radio-activity may not necesarily be a (main) player. It could be friction instead. Here is somebody who thinks likewise:


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