Researchers uncover 4 billion-year-old fossils

Microscopic tubes and filaments discovered in rock from the Hudson Bay shoreline in northern Quebec are "direct evidence" that life existed on Earth some 3.8 to 4.3 billion years ago, scientists said on Wednesday.

The microfossils in question are the mineralized remains of microbes similar to bacteria that thrive today around hydrothermal vents on the sea floor.

The tiny tubes were made of a form of iron oxide, or rust, formed by microbes encased in layers of quartz, according to a study published in the peer-reviewed journal "Nature."

The estimated age of the features surpasses the 3.7 billion years assigned to other rock features uncovered in Greenland that were proposed to be fossils last August.

The researchers expressed confidence that the fossils were formed by organisms and said that no non-biological explanation for the formations was plausible.

The finding lends credence to the hypothesis that hydrothermal vents may have been the cradle of life on Earth relatively soon after the planet was formed, the scientists said.

'Jury is still out'

Unlike digging up dinosaur bones, early-life findings are not as straight-forward. One of the key questions is whether the features trapped in the rock were formed by living organisms.

Wednesday's study hasn't convinced everybody in the field.

Martin J. Van Kranendonk of the University of New South Wales in Australia, who reported the Greenland findings last August, said the paper's evidence for a biological origin falls short.

"I would say they are not fossils," Van Kranendonk told the Associated Press.

NASA geologist Abigail Allwood told AP the study's authors produced "one of the most detailed cases yet made" for evidence of life over 3.5 billion years ago. However, she noted that "the jury is still out a little bit" as to whether the rocks are signs of past life.

rs/bw (AP, AFP, Reuters)