These scribbles may be some of the oldest fossil lives on Earth

A team of researchers in South Africa examined a piece of rock under a microscope and found the remains of a life of 3.42 billion years old. These fossils – the microscopic, wavy remains of organisms that lived on methane – expand the range of habitats suitable for life on Earth during the Archean Aeon.

Life was born long before the Cambrian Explosion of 541 million years ago, which heralded a new era of more complex underwater life. But the life before her (“Precambrian” life) seemed much less alive to the naked eye. The oldest signs of life on Earth are found in 3.5 billion year old rocks called stromatolites, clumps of petrified biofilm accretions. The newly discovered microfossils date from around the same time but represent a different form of life, a kind of microbe that thrived in an underwater hydrothermal system. The team’s results were published today in Science Advances.

“We found exceptionally well-preserved evidence of fossilized microbes that appear to have thrived along the walls of cavities created by hot water from hydrothermal systems a few feet below the seabed,” said Barbara Cavalazzi, a geobiologist at the University. from Bologna and principal author. paper, in a university Release. “Subterranean habitats, heated by volcanic activity, likely hosted some of Earth’s earliest microbial ecosystems and this is the oldest example we have found to date.”

The microfossils found by Cavalazzi’s team are ossified filaments; under the microscope, they look like cracks and blurry spots. Fossils are composed of carbon sheaths that house a core material distinct from the outer material, indicating a cell wall surrounding the intracellular substance. It is not very surprising to find life around a hydrothermal system; today, hydrothermal vents are teeming with life from another world. Such sites are not only interesting for understanding the origins of life on Earth but also for determining the conditions that could accommodate life on other worlds, such as Mars or the moons Europe and Enceladus.

The age of the fossils was based on the age of the rocks in which they were found, which had been determined in previous studies using chronology of zircons. Other job had identified Archean Eon microfossils in the same stone belt, so the team had good reason to believe they might find something exciting here. In the paper, the team notes that microfossils are putative, which means it is possible that they are something else and not a record of living things. They could have been artifacts of the hydrothermal system, something that could just look like life. With life forms so ancient and primitive, it is not that simple like looking for skeletons or fossilized footprints.

In these hydrothermal systems, cold seawater mixes with heated underground fluids, creating a chemical soup. Today, this soup is the delight of tube worms and crabs. In the Archean, such a complex life did not exist, but the microbes living on methane would have had a busy day. Concentrations of nickel in organic compounds in the fossil deposit match the nickel content found in modern microbes, the researchers noted, which are anaerobic (they survive without oxygen) and metabolize methane.

“The authors have gathered an impressive number of observations and present a convincing case that the filaments were once ancient microbes that inhabited fractures before they were buried by silica cement,” said Birger Rasmussen, a geobiologist at the University of Western Australia which was not affiliated with the recent paper. He noted that some will have questions about the shape of the filaments, and other experts may want more evidence that the microfossils were hollow, which would indicate the cellular structure of the filaments.

“These quibbles aside, this finding is certainly intriguing and points to the possibility that microbial life inhabited the nooks and crannies below the Earth’s surface more than 3.42 billion years ago,” Rasmussen said. “Time will tell if they are considered probable or possible microfossils, or whatever.”

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