Deep Divisions in the Tree of Life: What Does the Fossil Record Reveal?

The accurate dating of the antiquity of the major biologic lineages has posed a major challenge to Precambrian paleobiologists. The main difficulty lies in the fact that early fossil record is too incomplete to give precise answers. Another difficulty is that fossils and related remnants can provide only a minimum age for a lineage. The challenge is, therefore, to unify the competing lines of evidence and to conduct careful paleobiologic studies of additional rock units older than about 2200 Ma.