Radioactive elements were incorporated into the Earth when the Solar System formed.All rocks and minerals contain tiny amounts of these radioactive elements.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.As one answer to his critics, Kelvin produced a completely independent estimate -- this time for the age of the Sun.A commonly used radiometric dating technique relies on the breakdown of potassium (Ar in an igneous rock can tell us the amount of time that has passed since the rock crystallized.If an igneous or other rock is metamorphosed, its radiometric clock is reset, and potassium-argon measurements can be used to tell the number of years that has passed since metamorphism.Carbon-14 is a method used for young (less than 50,000 year old) sedimentary rocks.
It's this resetting process that gives us the ability to date rocks that formed at different times in earth history.
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.
This just goes to show that just because independent estimates of age seem to agree with each other doesn't mean that they're correct - despite the fact that this particular argument is the very same one used to support the validity of radiometric dating today.
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.