Lava rocks contain traces of ancient microbes

Tiny bacteria-size filaments and tubes have been found in 3.5-billion-year-old lava deposits from South Africa. They are strong evidence that ancient microbes ate their way into the glassy rock as it cooled deep on the ocean floor, researchers write in tomorrow's edition of the journal Science.

Earth's earliest organisms may have liked it hot, according to scientists. New fossils bolster claims that early life may have been linked to volcanic environments.

"This is by far the best evidence I've seen for extremely early life on Earth," commented Martin Fisk, oceanographer at Oregon State University in Corvallis. The style of the pits and fossilized tubes in these ancient pillow lavas are identical in appearance to the marks left behind by bacteria in lava that cools today on the ocean floor, Fisk said. "Pillow lava" is the term used for groups of rounded masses of lava formed underwater.

Most geologists searching for signs life in the oldest rocks have been looking at sedimentary deposits, not volcanic rock, Muehlenbachs said. A more established theory on the evolution of life holds that organisms first developed in warm, mineral-rich tidal pools, where sedimentary deposits might accumulate, he said, inform nationalgeographic.com

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," report sciam.com

According to BBC the rock has not lain unaltered since Archaean times: "It was pushed down into the Earth and cooked at well over 300 degrees (Celsius) for millions of years."

As the rocks were squeezed and heated, they "metamorphosed". Volcanic glass transformed into a mineral called chlorite. But this was a subtle conversion, say the researchers, which preserved original structures such as the microtubules.

The team claims observations of the fine structure of the burrows show they were overgrown by chlorite after being pushed beneath the Earth.