Back story: history of a hypothesis.

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April 1953

James Watson (left) and Francis Crick discover the structure of DNA, finding it can be replicated. The find set the stage for the discovery of RNA.

May 1953

Stanley Miller and Harold Urey's experiments suggest that amino acids, protein building blocks, spontaneously arose in the young Earth's primordial soup.

1960s

Sydney Brenner, Francois Jacob and Matthew Meselson show that messenger RNA (above) carries the information required to make proteins.

1967

Carl Woese and, later, Crick and Leslie Orgel independently propose that RNA may have been the earliest repository of genetic information.

1986

Walter Gilbert (shown) coins the phrase "RNA world" for the early Earth environment in which RNA stored information and replicated itself.

1989

Thomas Cech and Sidney Altman share the Nobel for finding that certain RNA molecules, called ribozymes, can cut and join each other--replication.