This microscope image made available by Matthew Dodd shows tiny tubes in rock that appear to be the oldest known fossils.
Tiny, tubular structures uncovered in ancient Canadian rocks could be remnants of some of the earliest life on Earth, scientists say.
The straw-shaped "microfossils," narrower than the width of a human hair and invisible to the naked eye, are believed to come from ancient microbes, according to a new study in the journal Nature. Scientists debate the age of the specimens, but the authors' youngest estimate - 3.77 billion years - would make these fossils the oldest ever found.
Claims of ancient fossils are always contentious. Rocks as old as the ones in the new study rarely survive the weathering, erosion, subduction and deformation of our geologically active Earth. Any signs of life in the rocks that do survive are difficult to distinguish, let alone prove. Other researchers in the field expressed skepticism about whether the structures were really fossils, and whether the rocks that contain them are as old as the study authors say.
But the scientists behind the new finding believe their analysis should hold up to scrutiny. In addition to structures that look like fossil microbes, the rocks contain a cocktail of chemical compounds they say is almost certainly the result of biological processes.
If their results are confirmed, they will boost a belief that organisms arose very early in the history of Earth - and may find it just as easy to evolve on worlds beyond our own.
"The process to kick-start life may not need a significant length of time or special chemistry, but could actually be a relatively simple process to get started," said Matthew Dodd, a biogeochemist at University College London and the lead author of the paper. "It has big implications for whether life is abundant or not in the universe."
The microfossils were discovered in rocks from the Nuvvuagittuq belt in northeastern Canada. This strip of iron-rich jasper now cuts across the eastern shore of Hudson Bay, but it was once a hydrothermal vent on the ocean floor. Billions of years ago, Dodd and his colleagues say, ancient microbes flourished around those vents, taking advantage of their chaotic chemistry to generate fuel.
When the microbes died, iron in the water was deposited on their decaying bodies, replacing cellular structures with stone. The rocks that contained them were buried, heated, squashed, and then forced upward to form the part of North America where they now sit.
The Nature paper comes just six months after researchers working in Greenland reported finding ancient stromatolites in 3.7-billion-year-old rocks. Those structures are usually produced by photosynthetic bacteria living in shallow seas. If both papers are confirmed, Slack explained, that means life not only existed early in Earth's history, but was diverse enough to include both chemosynthetic and photosynthetic bacteria.