Helium in the atmosphere. Evidence for or against a young earth?

And you would be correct: back 4,560,000,000 years ago or so, when there were bunches of radioisotopes like aluminum-26 and manganese-53 around our neighborhood, the Earth and/or the planesimals that came together to form it were much more radioactive than today. But all of those isotopes with half-lives of less than 80,000,000 years have now decayed: you'll only find them near the dying stars that synthesize them, or in nuclear laboratories. You can find magnesium-26 and chromium-53, the daughters of the two I mentioned, in minerals (in meteorites) where they "don't belong" chemically. They got there through nuclear dacay. Long ago.ABE: "dacay" is much more often spelled "decay."This message has been edited by Coragyps, 09-16-2005 04:13 PM