The fossilised remains of the oldest known lifeforms on Earth unearthed in Australia has proved that bacteria thrived in an oxygen-free world more than 3.4 billion years ago – a finding that should boost the search for life on Mars, scientists say.
The finding suggests early life was sulphur-based, living off and metabolizing sulphur rather than oxygen for energy.Until now, though, evidence has been indirect — namely, flecks of organic carbon, the putative remains of ancient microbes embedded in some of the oldest rocks on Earth.
"At last we have good solid evidence for life over 3.4 billion years ago," senior researcher Martin Brasier of Oxford University said in a statement.
“It confirms there were bacteria at this time, living without oxygen.”
Even today, hardy microbes near deep-sea vents and in other oxygen-starved environments thrive by consuming sulfur compounds. With no oxygen to breathe, their ancient relatives apparently did the same and probably belched hydrogen sulfide — the rotten-smelling gas popular with high school chemistry teachers.
The finding should boost the search for life on Mars, said David Des Marais, an astrobiologist at the NASA Ames Research Center.
“I mean, wow, we now know that sulphur-based metabolism happened very early on Earth. And early Mars had water and sulfur. It shared in many ways the environment of the early Earth,” The Washington Post quoted him as saying.
“This gives us confidence that looking for these types of organisms on Mars is a good strategy,” he added.
The study has been published in the journal Nature Geoscience.