"These traces of bacteria are the oldest fossils ever described. Those are our oldest ancestors," said Nora Noffke, a biogeochemist at Old Dominion University in Norfolk who was part of the group that made the find in Western Australia's Pilbara region.
If the fossils are proved to be this old, it could move scientists one step closer to understanding the first chapters of life on Earth. The discovery could also spur the search for ancient life on other planets, The Washington Post reported.
Unlike dinosaur bones, the newly identified fossils are not petrified body parts. They're textures on the surfaces of sandstone thought to be sculpted by once-living organisms.
Noffke and her colleagues measured the carbon that makes up the textured rocks. About 99 per cent of carbon in non-living stuff is carbon-12, a lighter version of the element than the carbon-13 that accounts for most of the remaining one per cent.
Microbes that use photosynthesis to make their food contain even more carbon-12 and less carbon-13. That bias, a signature of 'organic' carbon that comes from a living being, showed up in the Australian rock.
Most microbial mats today contain lots of photosynthetic cyanobacteria, which make the food that sustains the other bacteria.
Named after the blue-green pigment they use for this process, called phycocyanin, cyanobacteria also make oxygen and are given the credit for creating Earth's atmosphere about 2.4 billion years ago.
Cyanobacteria living in microbial mats nearly 3.5 billion years ago could shake up the history of the air we all breathe, the paper said.
"Studying this kind of past life is really about learning how the Earth got to be the way it is today," said Michael Tice, a geobiologist at Texas A&M University.
The research was presented at a meeting of the Geological Society of America.
