Chamberlain (1899) pointed out that Kelvin's calculations were only as good as the assumptions on which they were based.
But in general, this rate is felt by the vast majority of mainstream scientists to be a fundamental constant. al., published a paper suggesting that the decay rate of radioactive elements is related to the Earth's distance from the Sun.
In other words, the decay rates show annual changes that closely reflect the Earth's distance from the Sun (see illustration).
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.
Both the physical geologists and paleontologists could point to evidence that much more time was needed to produce what they saw in the stratigraphic and fossil records.