After all, the ever-changing Earth rarely left a complete geological record.
Unlike people, you can’t really guess the age of a rock from looking at it.
For organic materials, the comparison is between the current ratio of a radioactive isotope to a stable isotope of the same element and the known ratio of the two isotopes in living organisms.
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.
But it wasn't until the late 1700s -- when Scottish geologist James Hutton, who observed sediments building up on the landscape, set out to show that rocks were time clocks -- that serious scientific interest in geological age began.
Before then, the Bible had provided the only estimate for the age of the world: about 6,000 years, with Genesis as the history book.