( ompressed so much that their minerals a...)UCLA scientists strengthen case for life more than 3.8 billion years ago

Why Akilia Island in Greenland?

"Akilia Island was not the best place to search for evidence of early life; it's simply the place where it turned up," Harrison said.

"There's nothing special about Akilia Island," Manning said. "If life was there, it should have been abundant on Earth 3.83 billion years ago. The only place where that's been tested so far, also in Greenland, has come up positive."

One of the key methods for dating the rocks is by carefully analyzing cross-cutting intrusions made by igneous rocks, Manning said, adding, "Whatever is cross-cut must be older than that which is doing the cross-cutting. We went there to find these cross-cutting relationships, which we did."

The research on the Akilia rocks is federally funded by the National Science Foundation (http://www.nsf.gov/) and the NASA Astrobiology Institute (http://nai.arc.nasa.gov/), a partnership between NASA, 12 major U.S. teams and six international consortia.

Scientists look for evidence of life in ancient rocks like those from Akilia Island by searching for chemical suggestions and isotopic evidence. The very strong isotopic evidence for ancient life found in the 1996 study included a high ratio of one form of carbon--an isotope--to another, which provides a "signature of life," Mojzsis said.

The carbon aggregates in the rocks have a ratio of about 100-to-one of 12C (the most common isotope form of carbon, containing six protons and six neutrons) to 13C (a rarer isotopic form of carbon, containing six protons and seven neutrons). The light carbon, 12C, is more than 3 percent more abundant than scientists would expect to find if life were not present, and 3 percent is very significant, Harrison said.

Carbon inclusions in the rocks were analyzed w
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Source:University of California - Los Angeles