dmehling Posted April 29, 2012 Share Posted April 29, 2012 Is it true that radioactive elements contained within igneous rocks do not begin to decay until the magma from which these rocks were formed begins to cool? If so, why does the decay not begin until the magma cools? Link to comment Share on other sites More sharing options...
John Cuthber Posted April 29, 2012 Share Posted April 29, 2012 Is it true that radioactive elements contained within igneous rocks do not begin to decay until the magma from which these rocks were formed begins to cool? No. However the decay products can be left behind in the rest of the magma when the minerals crystallise out so, at the time the crystal forms there might be (for example) uranium, but no lead (or, at least, very little lead). Link to comment Share on other sites More sharing options...
swansont Posted April 29, 2012 Share Posted April 29, 2012 Or Ar gas trapped in the crystal, in the case of K-Ar dating. The "clock" starts when the magma cools, not the decays. Link to comment Share on other sites More sharing options...
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