The oldest traces of life on Earth occur in cherts (silicified volcanic silts and sands) that were deposited in coastal environments ∼3.5 billion years ago [1, 2, 3, 4, 5, 6]. These microfossils are the remains of relatively evolved organisms, implying that life had to have appeared much earlier . However, studies related to the origin of life are hampered by the fact that suitable rocks dating from the first billion years are lacking on Earth, since older materials are too heavily metamorphosed or have been destroyed by plate tectonics. Investigations are now focussed on the search for older microfossils on other planets and, in particular, on Mars. Mars does not appear to have undergone plate tectonic activity as on Earth and, if life appeared on that planet, its fossilised traces could be found embedded in rocks from th
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