Question

How do scientists estimate the age of the earth?

Answer 1

See explanation...

Explanation:

Primarily a combination of radiometric dating of Earth rocks, moon, rock, meteoritic rock and a plausible model of how the solar system formed.

Radiometric dating of Uranium is particularly useful. Both `""^238U` and `""^235U` decay into isotopes of lead with different but long half lives, approximately `4.5` billion years and `700` million years respectively. So the different uranium/lead ratios provide a good cross check.

One challenge is to find really early rocks near the surface of the earth. The earliest Earth rock dated are some zircon inclusions in rocks found in Australia at about `4.4` billion years.

The moon has not been subject to so much vulcanism, and the oldest moon rock that we have tested has been dated at about `4.51` billion years.

Meteorites have been dated between `4.53` and `4.58` billion years.

From our understanding of how the solar system formed, that results in an estimated `4.54` billion year age for the Earth.