December 17, 2004

BY DAVE NEWBART Staff Reporter

Nearly 4 billion-year-old rocks from Greenland could hold the earliest evidence of life on Earth, University of Chicago and Field Museum scientists say.

The rocks, the researchers argue in today's edition of the journal Science, are sediment of such composition that they could contain evidence of early life.

The finding is significant within an ongoing debate. Scientists in 1996 said they found evidence of microbial life in the Greenland rocks. But others have argued that the rocks couldn't have kept early evidence of life because they appeared to have originated as lava.

"My results show unambiguously that the rocks are sediment deposited at the bottom of an ocean,'' not igneous rock cooled from a molten state, said Nicolas Dauphas, assistant professor of cosmochemistry at the University of Chicago and a Field associate. "This is an important result.''

The scientists said the next step is to look in the rocks for traces of early life. Study co-author Meenakshi Wadhwa, associate curator in the museum's geology department, said the rocks also contain relatively high oxygen levels for the period, possibly signaling bacteria involved in photosynthesis. But both scientists emphasized they haven't found definitive evidence of life.

Conflicting conclusions

The rocks are from Akilia Island off the southwest coast of Greenland. They have fascinated scientists because of their age and high concentrations of iron, which needs oxygen -- a bedrock of life -- to form.

Dauphas used a mass spectrometer at the Field to analyze iron isotopes in the rock that wouldn't have changed over the years, he said. The $750,000, state-of-the-art spectrometer heated samples to 8,000 degrees, separated the isotopes through a high-powered magnet and then measured atomic variations in the iron. The process found isotopic signatures not common in lava, meaning they had to be sediment, Dauphas said.

Ariel Anbar, a geology professor at Arizona State University, said the paper boosts the argument there are signs of life there.

But Chris Fedo, an associate geology professor at George Washington University, said the rocks have changed too much to determine origins. He disputed their age and said his analysis indicated they could not sustain life.