Each of them typically exists in igneous rock, or rock made from cooled magma.
Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.
) is only 5,730 years—that is, every 5,730 years, half of it decays away.
After two half lives, a quarter is left; after three half lives, only an eighth; after 10 half lives, less than a thousandth is left.
The quantitative approach is admirable, but Buffon's assumptions are flawed. Silicate minerals have lower heat conductivity than steels and are better insulators leading to slower cooling rates.
Second, the calculations did not incorporate the heating effects of radioactive decay.