Why are fossils important in the study of molecular clocks?

Question

Why are fossils important in the study of molecular clocks?

Answer 1

Estimating species divergence times from molecular sequence data via phylogenetic trees is possible with the molecular clock, which allows the separation of rate and time by assuming a constant rate of molecular evolution. Unfortunately, species divergence times estimated using the molecular clock typically appear much more ancient than dates based on the fossil record.

        Hence calibration has to be done.

Error rate of DNA replication should be calibrated.

One method of calibrating the error rate was to use as references pairs of groups of living species whose date of speciation was already known from the fossil record.

For more info:

http://www.nature.com/hdy/journal/v94/n5...

http://en.wikipedia.org/wiki/Molecular_c...