How does a molecular clock measure time?

Question

Quizplus · Accepted Answer

A molecular clock measures time by counting the number of nucleotide substitutions over a fixed period of time. This is based on the assumption that mutations accumulate at a steady rate in the DNA sequence of the gene or region being studied. By comparing the number of differences in the DNA sequence between two species, and knowing the rate of mutation, scientists can estimate the time since the two species diverged from a common ancestor.

How Does a Molecular Clock Measure Time