Over half a billion years earlier than dates usually given. From ScienceDaily:
The researchers studied exceptionally well-preserved deposits which are approximately 3.5 billion years old in the ancient Dresser Formation in the Pilbara Craton of Western Australia.
They interpreted the deposits were formed on land, not in the ocean, by identifying the presence of geyserite – a mineral deposit formed from near boiling-temperature, silica-rich, fluids that is only found in a terrestrial hot spring environment. Previously, the oldest known geyserite had been identified from rocks about 400 million years old.
Within the Pilbara hotspring deposits, the researchers also discovered stromatolites – layered rock structures created by communities of ancient microbes. And there were other signs of early life in the deposits as well, including fossilised micro-stromatolites, microbial palisade texture and well preserved bubbles that are inferred to have been trapped in a sticky substance (microbial) to preserve the bubble shape.
“This shows a diverse variety of life existed in fresh water, on land, very early in Earth’s history,” says Professor Van Kranendonk, Director of the Australian Centre for Astrobiology and head of the UNSW school of Biological, Earth and Environmental Sciences. Paper. (public access) – Sara Djokic, Martin J. Van Kranendonk, Kathleen A. Campbell, Malcolm R. Walter, Colin R. Ward. Earliest signs of life on land preserved in ca. 3.5 Ga hot spring deposits. Nature Communications, 2017; 8: 15263 DOI: 10.1038/ncomms15263 More.
A bit of caution is well advised here because some of these early Pilbara finds have ben disputed as fossils of life (technically, they are then called “pseudofossils”).
The idea that early life is best sought in fresh rather than salt water competes with the oceanic hydrothermal vents thesis.
In any event, as we have noted before, if there was really a “diverse variety” of life back then, it would be fast work for purely Darwinian evolution.
See also: World’s “oldest microfossils” are not life forms after all.
Microbial mats show fossil structures from 3.5 billion years ago
Origin of life: Could it all have come together in one very special place?
What we know and don’t know about the origin of life
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