( ere as old as originally envisioned. We...)UCLA scientists strengthen case for life more than 3.8 billion years ago

At the time of the 1996 Nature paper, there was no reliable map showing the geology of the area, Manning said. So he created one.

"I wandered around that outcrop for two-and-a-half weeks--it's not a big area--with a clipboard, maps, a compass and grid paper. We mapped it like an archeologist would map it," Manning said. "It became clear that these rocks that hosted life line up into two beautiful, coherent layers. They are not randomly distributed, as you might expect if the alternative interpretation is right. I'm very confident about that. I went to Greenland with some skepticism, but I became more and more confident as time went on that the original interpretation was right."

"It could have gone any way," Harrison said. "We could have placed the claim on much firmer footing, or we could have proved ourselves wrong. We found a much more compelling cross-cutting relationship in the rocks than we originally thought."

The new research is a comprehensive response to the critics, Harrison said.

"We've been holding our fire rather than fire away at each criticism in a piecemeal way," he said. "We've gone back to Greenland and done the study from the ground up, with much more data than existed at the time of the original paper. I'm much more confident today than I was in 1996 about the likelihood that this is evidence of early life. This is not 'smoking gun' evidence--we are not seeing fossils--but in every case, the model has come through with flying colors."

Manning agrees, saying he is confident the rocks contain evidence of ancient life, but "it's not a slam dunk."

Why is there doubt? After more than 3.8 billion years, the rocks are severely damaged.

"They have been folded, distorted, heated and c
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Source:University of California - Los Angeles