Radioisotope dating fossils
In short, the assumption that decay rates are immune to outside influences isn't as solid as it once appeared to be.However, if one does assume a constant decay rate, and if one starts with an originally pure sample of “parent element,” then the proportion of parent to daughter tells us the number of half-lives, which has been used to find the supposed age of igneous rocks. The conclusions of Renne and his team read as follows: Ar can be identified in volcanic sanidine, and while perhaps negligible in pre-Holocene rocks, it has important consequences for sample at the limit of the method’s applicability.His result was in close agreement with his estimate of the age of the earth.
If magnetic fluxuations or other influencing forces are strong enough, radiometric decay rates could be much more significantly effected.
Without this knowledge, he argued that, "As for the future, we may say, with equal certainty, that inhabitants of the Earth cannot continue to enjoy the light and heat essential to their life, for many million years longer, unless sources now unknown to us are prepared in the great storehouse of creation."The same is true of the basis of Kelvin's estimate of the age of the Earth.
It was based on the idea that no significant source of novel heat energy was affecting the Earth.
He believed this even though he did admit that some heat might be generated by the tidal forces or by chemical action.
However, on the whole, he thought that these sources were not adequate to account for anything more than a small faction of the heat lost by the Earth.