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'Microfossils' Made Easy
14 November 2003 (All day)
Looks can be deceptive, as researchers looking for ancient and alien life have discovered. Those wormy-looking shapes in a martian meteorite turned out to be purely mineralogical and never were alive; and last year, researchers claimed that the textbook examples of the earliest known life on Earth--the 3.5-billion-year-old "Warrawoona" microfossils from Australia--are nothing more than suggestively shaped geologic detritus, not fossils (Science, 8 March 2002, p. 1812). Now, researchers have shown that minerals bearing a striking resemblance to the Warrawoona microfossils are surprisingly easy to cook up in the lab.
The recipe is rather simple: Combine silica, carbonate, and barium in an alkaline medium with a dash of simple organics. Geologist and crystallographer Juan Manuel García-Ruiz of the CSIC-University of Granada, Spain, and his colleagues mixed the inorganic ingredients at near room temperature and, at certain dilute concentrations of ingredients, produced sheets adorned with filaments, all composed of barium carbonate crystals coated with silica. The filaments look enough like true microfossils to be mistaken as the products of life, the authors say. And the lab conditions are similar to those at the time of the Warrawoona fossils, they say, to judge by the abundant carbonate, silica, and barium sulfate found among neighboring rocks.
What's more, when García-Ruiz and his colleagues immersed the synthesized filaments in a brew of formaldehyde and phenol, then heated the mix, a brown layer of complex organic matter coated the filaments--just as on the Warrawoona fossils. Heat-induced breakdown of iron carbonates, which could have happened at Warrawoona, produces relatively simple organic materials; with time, García-Ruiz argues in today's issue of Science, these materials could combine into complex organics, much as happened in the lab.
Some don't find the imitation-fossils convincing. "The resemblance is superficial," says William Schopf of the University of California, Los Angeles, who was first to publish on the Warrawoona fossils in Science in 1993 (30 April 1993, p. 640). But organic geochemist George Cody of the Carnegie Institution of Washington's Geophysical Laboratory says they "look remarkably 'lifelike.' "
That doesn't prove that paleontologists mistook inorganic minerals for fossils at Warrawoona, but it does remind everyone that "just because something looks familiar doesn't mean it's biogenic," says Cody. "A lot more thought has to go into biomarkers for ancient life."