Radioisotope dating problems
Because of the fairly fast decay rate of carbon-14, it can only be used on material up to about 60,000 years old.
These use radioactive minerals in rocks as geological clocks.
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.
Others measure the subatomic particles that are emitted as an isotope decays.
Some measure the decay of isotopes more indirectly.