All life on Earth is cellular and uses DNA to store genetic information. However, evidence suggests that, on ancient Earth, much complex chemical activity preceded cellular development, and it was probably not DNA-based at the start. What was the nature of this activity, and how did it lead to life? "Molecular evolution" is a term used to describe the stages that preceded the origin of life on Earth. The term implies that information-containing molecules were subject to the process of natural selection, whereby genetic structures were capable of both replication (the copying of specific nucleic acid sequences) and mutation. In addition, it is theorized that certain chemical reactions may have taken place on early Earth, before true evolution began, and some of these reactions may have helped to form these informational molecules that enabled replication and mutation.

The Antiquity of Life

The oldest known fossils date...