Scientists studying ancient creatures celebrate finds such as an ankle bone or jaw fragment because they help to piece together the varied history of our planets past inhabitants. But as investigators reach ever farther back in time, the evidence of early life becomes increasingly difficult to discern. A new discovery may help to fill in some of the blanks. Researchers report that tiny tubes in rocks that are billions of years old further suggest that microbes were eating their way into lava on the ocean floor during Earths early history.

Harald Furnes of the University of Bergen in Norway and his colleagues detected the trails in pillow lava from South Africas Barberton Greenstone Belt, which dates to 3.5 billion years ago. The diminutive tunnels, just four microns wide and about 50 microns long, look very similar to the product of microbial burrowing seen in modern volcanic rocks. In addition, the scientists detected carbon on the inside of the tubes, which they say is further evidence of the biogenic origin of the structures. The authors conclude that their findings "suggest that microbial life colonized these subaqueous volcanic rocks soon after their eruption almost 3.5 billion years ago."

The new report, which appears in the current issue of the journal Nature, is far from the final word in the search for Earths earliest life, however. Alternative processes--such as chemical reactions during decomposition of organic matter--could lead to similar markings. Instead, the new findings join other so-called biomarkers, such as characteristic ratios of carbon or sulfur isotopes and ancient hydrocarbons, found as far a field as Greenland to Australia at the head of the pack of primitive organisms. So scientists will need to continue searching for additional clues to the mystery of lifes origins.