Value of potassium argon dating to geologists
These two independent and agreeing dating methods for of the age of two primary members of the solar system formed a strong case for the correctness of his answer within the scientific community.
The isochron dating method theoretically overcomes the need to know the initial ratio of parent and daughter isotopes. For now, we will look at those methods that do fall under the above assumptions.Other factors and basic assumptions must also be considered.Of course, Kelvin formed his estimates of the age of the Sun without the knowledge of fusion as the true energy source of the Sun.His result was in close agreement with his estimate of the age of the earth.The solar estimate was based on the idea that the energy supply for the solar radioactive flux is gravitational contraction.Based on these assumptions he at first suggested an age of the Earth of between 100 Ma and 500 Ma.
This estimate was actually reduced over his lifetime to between 20 Ma and 40 Ma and eventually to less than 10 Ma. Perry, in particular, a noted physicists and former assistant to Kelvin, showed that cooling calculations using different but equally likely assumptions and data resulted in ages for the Earth of as much as 29 Ga.
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.
Of course there seem to me to be fairly reasonable explanations for this observation which may allow for more slowly forming granitic rocks.
For instance, polonium radiohalos are sometimes associated with polonium bands generated by the polonium being transported by hydrothermal fluids along fractures.
Chamberlain (1899) pointed out that Kelvin's calculations were only as good as the assumptions on which they were based.