Geotimes - January 2004 - Cooked minerals resemble life

Geotimes

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Mineralogy
Cooked minerals resemble life

A laboratory experiment has given rise to tiny filaments that mimic structures found in ancient rocks identified as microfossils. The findings cast further doubt over whether the oldest known microfossils found in the 3.5-billion-year-old Warrawoona Group in Australia were indeed produced by living organisms, with implications for the search for early life on Earth and elsewhere.

Field emission scanning electron microscopy images of twisted filaments made by a purely inorganic mechanism. Image courtesy of J.M. García-Ruiz.

In experiments reported in the Nov. 14 Science, J.M. García-Ruiz of the Consejo Superior de Investigacione Cientificas and the University of Granada, Spain, and Stephen Hyde and his team at the Australian National University, Canberra, and the Geological Survey of Western Australia, set up conditions where long filaments and sheets of crystals formed in a high-pH bath, a solution of barium salt and sodium silicate, at varying temperatures. Focusing on 5- to 10-micron-sized structures that formed at room temperature, they found a complex composite of inorganic and organic material, with tiny crystals of organic barium carbonate, enveloped by silica. After dissolving away the carbonate, the team found that the remaining hollow structures looked surprisingly like the tiny ropy caterpillar-like structures imprinted in the Warrawoona rocks.

The laboratory ecosystem was “geochemically plausible during the Archean,” García-Ruiz and his co-authors wrote. The required elements — from an alkaline medium to the presence of low-molecular-weight simple organic molecules such as phenol or formaldehyde — could have been at hand during the formation of the Warrawoona, which is rich in chert (SiO2), barite (BaSO4) and carbonate minerals. No life would have been necessary.

If the Warrawoona microfossils (found in two formations that differ in age by about 25 million years) are the oldest biological forms on Earth, says Robert Hazen of the Carnegie Institution of Washington, then that “implies life started very early and easily.” If not, then life likely jumpstarted after the planet was barren for billions of years, which seems as unlikely if not more so, he says.

Hazen says the new laboratory experiments are promising for future protocols to identify signatures of life at the microscale. However, he says, the team’s work has an “increasing number of special conditions,” which is always disturbing, when trying to apply Occam’s razor — the solution with the least number of assumptions.

“There’s a tremendous amount at stake here,” Hazen says, particularly for the astrobiology community. “If we can’t tell on Earth if it’s life, how can we go to Mars and determine it’s life?”

Naomi Lubick

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