Quebec fossil revises prehistory

LONDON • It’s life, but not as we knew it.

The oldest fossil ever discovered on Earth shows that organisms were thriving 4.2 billion years ago, hundreds of millions of years earlier than previously thought.

The microscopic bacteria, smaller than the width of a human hair, were found fossilized in rock formations along the eastern shore of Hudson Bay in Quebec, but would have lived in hot vents in the 60 C oceans that covered the early planet. The discovery is the strongest evidence yet that similar organisms may also have evolved on Mars, which at the time still had oceans and an atmosphere very similar to early Earth, and was being bombarded by the same comets that probably brought the building blocks of life to our planet.

The team that made the discovery, from University College London, believe that looking for similar fossils on the Red Planet is the best chance of finding evidence of alien life.

“Early Mars and early Earth are very similar places, so we may expect to find life on both planets at this time,” said doctoral student Matthew Dodd, the lead author of the study, which was cofunded by NASA. “We know that life managed to get a foothold and evolve rapidly on Earth. So if we have life evolving in hydrothermal vent systems maybe even 4.2 billion years ago when both planets had liquid water on their surface, then we would expect both planets to develop early life.

“If we do future sample returns from Mars and look at similarly old rocks and we don’t find evidence of life then this certainly may point to the fact that Earth might have been a very special exception, and life may have arisen just on Earth.”

Prior to this discovery, the oldest micro-fossils reported were found in Western Australia and dated to 3.4 billion years ago, leading scientists to speculate that life probably started around 3.7 billion years ago.

Abigail Allwood, a NASA geologist, said the authors have produced “one of the most detailed cases yet made” for evidence of life in rocks older than 3.5 billion years. But “it’s an extraordinary claim to make and you do need extraordinary evidence,” she said. While the rock features could be signs of past life, she said, “I think the jury is still out a little bit.”

The research was published in the journal Nature.

WE MAY EXPECT TO FIND LIFE ON (EARTH AND MARS) AT THIS TIME.