Para: My comments:
Isochron dating is based on the assumption that decay rates are constant. Statistical evidence
based on only a hundred years of observations is not sufficient support for such an assumption.
But we can see in the past. Remember the stars? SN1978A, a supernova showed evidence of constancy
of the decay rates. There is no evidence of a decay in the decay rates.
Rich Daniel added:
Kelvin didn't know about fission and fusion, which makes his calculations
That assumes that the earth gets most of heat from radioactive decay or the sun its heat from fusion. Again, the observational evidence of 100 years is insufficient to support these assumptions.
Wrong again. But radioactive decay as well as fusion of the sun have been observed.