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Oldest microfossils suggest life thrived on Earth about 4 billion years ago

hematite
SIGNS OF LIFE In rocks left over from ancient hydrothermal vents, these microscopic tubes of hematite, an ore of iron, may be remnants of early microbes.

Tiny, iron-rich fossils exhumed from the depths of an ancient ocean could reveal the cradle of life.

These micrometer-scale structures are probably remnants of microorganisms that once lived amidst ancient hydrothermal vents, researchers suggest March 1 in Nature.

“In a nutshell, what we’ve found are the oldest microfossils on Earth,” says study coauthor Matthew Dodd, a biogeochemist at University College London. The rocks that hold the fossils came from Quebec and date to somewhere between 4.28 billion and 3.77 billion years old — when Earth was still a baby. The next oldest microfossils reported are just under 3.5 billion years old, though their validity has been debated (SN: 2/8/14, p.16).

If Dodd’s structures truly are remnants of microbes, “it’s fantastic. I love it,” says astrobiologist Martin Van Kranendonk of the University of New South Wales in Sydney. But he’s not convinced. In fact, he says, “there’s just not definitive proof that any of the textures or the minerals or features they have is unique of life.”

Claims of early life are frequently fraught with controversy. For one, says Dodd, “these are big claims — these are our origins.” And scientists studying early life typically don’t have a lot to work with. It’s not like they’re looking at dinosaur bones. In billions-of-years-old microbes, obvious cellular bits and other familiar flags of life have often been stripped away. And in Earth’s oldest rocks, extreme heat and pressure can cook and squash any remnants of life…