Traces of Early Life Here's an interesting news item from Scientific American:
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 planet’s 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 Earth’s early history.
Harald Furnes of the University of Bergen in Norway and his colleagues detected the trails in pillow lava from South Africa’s 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 Earth’s 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 life’s origins. --Sarah Graham
One of the reasons the origin-of-life is such a vexing problem for scientists is the extreme rarity of any direct evidence for what conditions were like on the early-Earth. For that reasons, finds like the one described above are crucial.
It's also interesting, however, that there are no completely unambiguous signs of life in the Earth's most ancient rocks. If so much as a fossilized worm were found in rocks of that age, evolutionary theory would receive a serious blow. Happily, no such find has ever been made.