What is the term for using mutation rates to estimate evolutionary divergence times?

The term for using mutation rates to estimate evolutionary divergence times is the molecular clock.

The method compares DNA, RNA, or protein sequences from different organisms. If mutations accumulate at an approximately known rate, the number of molecular differences can provide an estimate of how long ago their lineages split. Scientists usually calibrate the estimate with fossils, geological events, or other dated evidence.

The molecular-clock idea was associated with Émile Zuckerkandl and Linus Pauling, who reported in 1962 that amino-acid differences in hemoglobin tended to increase roughly with evolutionary time. The approach helped turn molecular comparisons into a tool for reconstructing the history of life.

The clock is not perfectly regular. Mutation rates can differ among genes, lineages, generations, and time periods, so modern analyses often use relaxed-clock models rather than assuming one universal rate. A molecular clock estimates divergence; a phylogenetic tree shows relationships, while cladistics is a method for inferring those relationships.