Hotly debated 3.5 billion-year-old microbe fossils get another look

Enlarge / Optical microscope image of one of the purported microfossils on the left, and a Scanning Electron Microscope image of the same spot after carbon isotopes were measured in three pits on the right. (credit: Schopf et al./PNAS)

The title of “oldest evidence of life” has been provisionally claimed by a growing and confusing crowd of discoveries recently. At least until the last few years, the crown rested comfortably on a 3.47 billion-year-old rock from Western Australia called the Apex Chert. First described in the early 1990s, this rock contained a variety of microscopic structures that looked for all the world like the fossilized remains of microbial life.

Like other finds in this category, the Apex Chert has seen its fair share of controversy as researchers skeptically poked and prodded. Just two years ago, we covered a study that concluded these microfossils were simply clever lookalikes created by minerals crystallizing near a hydrothermal vent. In that version of events, some carbon (which may or may not have come from living things) stuck to vaguely microbe-shaped mineral crystals.

A recent study led by William Schopf—who discovered the Apex Chert in the first place—brings newer tools to bear on the question. And the researchers believe the results show that these microfossils are not impostors.

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