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The same painting can strike one person as genius and another as pedestrian. But this effect is not unique to the world of art, as opposing views of the same data published today in the journal Nature, illustrate. At the center of this controversy lies not a canvas, but a 3,465 million-year-old rock that may or may not harbor the earliest bacteria fossils yet.
Previous work led by J. William Schopf of the University of California at Los Angeles had suggested that so-called Apex chert specimens from western Australia could contain bacteria fossils based on a study of morphology alone. But because bacteria have very little morphology to speak of, the claims were understandably controversial. In the new work, Schopf and colleagues examined the material using a technique known as laser-Raman spectroscopy, which allowed them to map the chemical composition and the structure of the fossils in two dimensions. The team first tested the spectroscopic technique on four more established fossil specimens before examining the Apex sample. When they did analyze the Apex chert, they detected chemical compositions consistent with organically derived carbon, a sign of life. The team concludes that "by the time of preservation of the diverse, exceptionally ancient, microscopic filaments of the Apex chert, [approximately] 3,500 million years ago, microbial life was flourishing and presumably widespread."
In a second paper contesting this conclusion, Martin D. Brasier of the University of Oxford and his colleagues argue that the rocks from which the fossils were recovered may have belonged to a vein produced by hydrothermal action. They propose that the detected carbon signature could be a result of carbon dioxide transformed into carbon at temperatures between 250 and 350 degrees Celsius. Moreover, the team also suggests that the arrangement of the structures thought to be fossils is random and uncharacteristic of bacterial behavior. Considering that the next contender for the oldest-life crown is 1,000 million years younger than the Apex chert material, a consensus in this case is eagerly anticipated, though it may be a long time coming.
