Question

When researchers use a molecular clock what are they measuring?

Answer 1

1.The time that two species have been evolving independently
2.The time that fossils have been buried
3.The number of neutral mutation in a genome
4.How long ago an organism went extinct

My answer is number 3, can anyone help me verify?

Answer 2

its two

Answer 3

I know for a fact it is not 2.