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A new report adds to the controversy over the origin of the world's oldest known fossils [Science, 302, 1194 (2003)]. Juan Manuel García-Ruiz at Spain's University of Granada; Stephen T. Hyde at Australian National University, Canberra; and coworkers found that filaments self-assembled from BaCl2 and alkaline sodium silicate solutions at mildly hydrothermal temperatures (left) closely resemble the approximately 3.5 billion-year-old microfossil filaments (right) from the Precambrian Warrawoona chert formation in Western Australia. Many scientists had concluded that the microfossils originate from cyanobacteria. But because García-Ruiz and Hyde's group synthesized filaments under conditions similar to the ambient surroundings of 3.5 billion-year-old Western Australia, they speculate that the microfossils may not have formed biogenically. Furthermore, they suggest that particulate carbon residue--generally thought to derive from polyaromatic hydrocarbons and considered proof of biological origin--may actually come from high-temperature reactions of iron carbonates and water.
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