Question: How do u know it's 3.2 billion years old?

Vincent Monchal answered on 1 Dec 2022:

I use the chemical composition of a rock, then I solve some mathematical equations about radioactive decay with the composition I found, and the result of the equations give me the age.
The most common example of dating technique is Carbon 14 that you see in series to date a bone, for rocks we can’t use Carbon, so we use Uranium but the principle is the same.