A discovery in Western Australia may have shined a light on the Earth’s oldest inhabitants, with researchers finding microbes in rocks over three and a half billion years old.

An international team working in WA’s Pilbara region found evidence of a complex microbial life-form within sediment.

Scientists called them ‘MISS’, or microbially-induced sedimentary structures, and the latest occurrence of the incredibly early Earth inhabitants were found in a rocky area called the Dresser Formation, west of Marble Bar.

“They could be the oldest evidence for life on Earth,” University of Western Australia researcher David Wacey said.

“We have found micro-fossils and stromatolites of about the same age, but they are generally a little bit younger, so this could just push back evidence for life on Earth by a few more million years.”

The “signs of life are basically degraded parts of microbes that you no can longer see their form,” Wacey said

“You can't see cells any more but what you can see is basically carbonaceous material, which are the remnants of these cells.

“And, what's happened is that when they were alive they were interacting with the sediment where they were living and they were creating little communities where they were all kind of helping each other out to survive in what would have been a very harsh environment back then.”

The researchers were thrilled to find what appears to be a complex array of ancient inhabitants.

“To find a whole community of these things and to see that they were interacting with each other and interacting with the sediment they were growing on, you can think of it almost like a microbial city and they're all communicating with each other and stabilising the environment they were living in so they could all survive,” Mr Wacey said.

Western Australia is a hotspot for discoveries of rocks which have not moved since soon after the Earth was formed.

“There are some older rocks on the planet,” Mr Wacey said.

“There's some in Greenland but they've been deformed more so it's very hard to see what the original structure of the rock was, whereas these have had very little deformation to them and they essentially look pretty much like they would have done billions of years ago.”

More details of the exciting find are available from the official report.