A team of researchers in South Africa put a bit of rock under a microscope and found the remains of 3.42-billion-year-old life. Those fossils—the squiggly, microscopic remains of organisms that subsisted on methane—broaden the scope of what habitats were suitable for life on Earth during the Archean Eon.
Life originated long before the Cambrian Explosion of 541 million years ago, which heralded a new era of more complex undersea life. But the life before it (“Precambrian” life) looked a lot less alive to the naked eye. The oldest signs of life on Earth are found in 3.5-billion-year-old rocks called stromatolites, piles of petrified accretions of biofilms. The newly discovered microfossils date to nearly the same time but represent a different form of life, a sort of microbe that thrived in a submarine hydrothermal system. The team’s results were published today in Science Advances.
“We found exceptionally well-preserved evidence of fossilised microbes that appear to have flourished along the walls of cavities created by warm water from hydrothermal systems a few meters below the seafloor,” said Barbara Cavalazzi, a geobiologist at the University of Bologna and lead author of the paper, in a university release. “Sub-surface habitats, heated by volcanic activity, are likely to have hosted some of Earth’s earliest microbial ecosystems and this is the oldest example that we have found to date.”
The microfossils Cavalazzi’s team found are ossified filaments; under a microscope, they look like cracks and fuzzy splotches. The fossils are composed of carbon sheathes that ensconce central matter that is distinctly separate from the external material, indicative of a cell wall surrounding intracellular stuff. It’s not terribly surprising to find life around a hydrothermal system; today, hydrothermal vents teem with otherworldly life. Such sites are not only interesting for understanding the origins of life on Earth but also for determining the conditions that could host life on other worlds, like Mars or the moons Europa and Enceladus.
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