3.5-Billion-Year-Old Lava Yields Signs of Early Life

John Pickrell
for National Geographic News
April 22, 2004

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.

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.

"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.

Primordial Puzzle

There are a number of other pieces of evidence of life collected from extremely old rocks, but these have been vigorously debated. Possible examples of the earliest bacterial fossils are from 3.5-billion-year-old rocks from Western Australia. These examples, though, are not universally accepted as valid.

In 1996 scientists argued that they had found chemical evidence of life in 3.8-billion-year-old rocks from western Greenland. The evidence came from pockets of a type of carbon, known as light carbon, which living organisms today accumulate.

Now geologist Harald Furnes of the University of Bergen in Norway and colleagues in North America and South Africa may have found the strongest evidence so far that our planet was teeming with primordial life 3.5 billion years ago—though perhaps not in the most obvious places.

Scientists already knew that some kinds of bacteria are able to munch their way into man-made glass, dissolving it to extract nutrients. Then in the early 1990s Furnes and his team found evidence from deep-ocean drilling projects that bacteria also dig their way into naturally formed glassy rocks.

These rocks form in the top few hundred meters of the ocean floor, said Furnes's co-author, geochemist Karlis Muehlenbachs of the University of Alberta in Edmonton, Canada. "Basalt lava chills instantly into glass when it comes into contact with cold water," Muehlenbachs said.

To back up their claims, the scientists used an x-ray technique and found traces of organic carbon, phosphorous, and nitrogen—chemical signatures of life—in the tiny bacterial burrows but not in the surrounding rock. Furthermore, researchers have been unable to reproduce the same markings using chemical processes alone.

"These marks provide unmistakable evidence that organisms live in these [modern] rocks," agreed Oregon State's Fisk, who was not involved in the new study.

The next logical step was to look for the same evidence of life in older deposits, said Muehlenbachs, and the scientists have subsequently found similar markings in 100-million-year-old volcanic rock from Cyprus, and 430-million-year-old rocks from Norway.

Continued on Next Page >>




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