Constructing life

Any recipe for life on Earth requires a source of essential elements, a source of energy to stimulate chemical reactions between these elements, and time for these reactions to take place.

In 1952 researchers at the University of Chicago took a mixture of ammonia, methane, and hydrogen to simulate the early Earth atmosphere and applied a spark to simulate a natural source of energy-lightning-and after 8 days found that amino acids—the building blocks of DNA-- had formed in this oxygen-free atmosphere.

In the half-century since this experiment scientists have modified their ideas about the composition of the early earth atmosphere, but the Miller-Urey experiment still stands as the first example of synthesizing organic compounds from inorganic precursors—a process that occurred in the Early Earth in some form, as our own existence is evidence that it happened.

For more on the Miller/Urey experiment, see this site.

The search for earliest life, continued

Identifying traces of life in very ancient rocks is understandably difficult, and more than one claim for the oldest evidence of life later has not withstood scrutiny after making its initial splash in the headlines or even after being incorporated into textbooks. Tiny structures initially identified as microfossils have been reinterpreted to be the result of inorganic rather than organic processes.

A recent discovery, however, offers convincing evidence for the presence of relatively large, organic-walled microfossils in rocks 3.2 billion years old from South Africa. The structures are interpreted as organic on the basis of their cell-like morphology and ultrastructure, the fact that they occur in large numbers, as would microfossils, and their presence in rocks that represent environments that would have been amenable to living organisms. Time will tell.

Source and photo credit: Javaux, E.J., et al., 2010. Organic-walled microfossils in 3.2-billion-year-old shallow-marine silicilastic deposits. Nature 463:934-938.