3.8- billion- year- old bacteria may be Earth’s oldest fossils

They could bring hope of finding life on other planets

Scientists found traces of bacteria living more than 3.7 billion years ago, an age that would make them — if confirmed — the oldest- known fossils and bolster the idea that life got off to a running start on Earth, and perhaps elsewhere.

The bacteria lived near hy- drothermal vents, cracks in the seafloor that gush hot, mineralladen water into the open ocean, say the scientists who identified the fossils. Verification of the finding could make ocean vents on other planets in the solar system a key target in the search for extraterrestrial life.

“It’s exciting to find life had managed to get a grip and start to evolve on Earth so quickly after the planets formed,” says Matthew Dodd of Britain’s University College London, co- author of a study in this week’s Nature that describes the fossils. “It gives me … high hopes of finding life elsewhere in the universe.”

The rock in which the fossils reside is at least 3.77 billion years old and could be 4.28 billion years old. The next- oldest confirmed fossil is 3.5 billion years old, the study says. Last year, scientists reported the discovery of stromatolites — formations built by ancient microbes — dating to 3.7 billion years ago.

When Dodd began examining slivers of rock collected from Quebec, he saw something strange: thread- like filaments half as wide as a human hair and slightly thicker cylinder- shaped tubes. Both filaments and tubes were composed of an iron- rich mineral.

Similar filaments are excreted by modern bacteria that consume iron, says co- author Dominic Papineau, also of University College London. Such filaments and tubes have been seen in much younger “microfossils” found in Norwegian rocks.

The researchers also spotted rosette- shaped formations, which the scientists argue could have blossomed through a chemical process that began with rotting bacteria.

The rosettes are freckled with dots and shards of other chemicals linked to life, such as phosphorus, a key ingredient for biological activity.

M. DODD A microscopic iron- carbonate rosette with concentric layers of quartz containing tiny bits of red hematite may be a sign of oxidation of microbes that lived near undersea vents.