In a new study, researchers have discovered traces of bacteria that lived a record-breaking 3.49 billion years ago, a mere billion years after Earth formed.
If the find withstands the scrutiny that inevitably faces claims of fossils 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.
According to Nora Noffke from Old Dominion University in Norfolk, these traces of bacteria a, the Sydney Morning Herald 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.
Today, similar patterns decorate parts of Tunisia’s coast, created by thick mats of bacteria that trap and glue together sand particles. Sand that is stuck to the land beneath the mats and thus protected from erosion can over time turn into rock that can long outlast the living organisms above it.
Finding the earliest remnants of this process required a long, hard look at some of the planet’s oldest rocks, located in Western Australia’s Pilbara region.
This ancient landscape was once shoreline. Rocks made from sediment piled up billions of years ago are now exposed and available for examination. Relatively pristine in condition, such outcrops, along with others in South Africa, have long been a popular place to look for traces of life from the Archean aeon, which ended 2.5 billion years ago.
There are older rocks on Earth, said Maud Walsh, a biogeologist at Louisiana State University in Baton Rouge. Many of the textures seen in the Australian rocks had already shown up in 2.9-billion-year-old rocks from South Africa, reported on by Noffke and colleagues in 2007.
Still, old Australian rocks have proved deceptive before. As early as 1980, rippling layers within the Strelley Pool were thought to be the handiwork of bacteria. But such stromatolites, which are different from the structures that Noffke studies, can also be the work of natural, non-living processes.
For instance, water flowing along a seafloor can create similar structures under the right conditions. So can spraying jets of liquid loaded with particles onto a surface, as scientists at Oxford University demonstrated in laboratory experiments.
That’s why Noffke and her colleagues corroborated their story by measuring the carbon that makes up the textured rocks. About 99 percent 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 1 percent.
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. What wasn’t preserved was any proteins or fats or body fossils that would clinch the case for life and identify what types of bacteria left behind this organic carbon.
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 findings of the study were presented at a meeting of the Geological Society of America.