January 2, 2013.
Rocks that grew from bugs? Some of the oldest fossils on the planet are sedimentary rocks that were once living organisms. Western Australia is famous for both living and fossilized examples of these early Earth inhabitants. The most well studied of these microbially-built structures are called stromatolites, and they grow in a wide-range of environments: from the shore, underwater, to inland across arid salt-flats.
The ecosystems that generated Earth's oldest stromatolites also produced other types of what biogeochemist Nora Noffke of Old Dominion University in Norfolk, Va., calls microbially induced sedimentary structures or MISS. "These structures represent an entire ecosystem of surprising diversity," she says. They may even rival stromatolites with fossils dating back 3.49 billion years.
The microbes that built these ancient structures “are the oldest fossils ever described. Those are our oldest ancestors,” Noffke told the Washington Post. She and her team presented their analysis last month at a meeting of the Geological Society of America.
Like stromatolites, these other microbial mats hold minerals and sand particles in their matrix, preventing erosion of the land around them. After they die, the sand eventually turns to sandstone and preserves the mats as fossils.
Noffke and her team looked in Western Australia’s Pilbara region for the community of fossil organisms turned to stone. Their discovery still needs additional scrutiny to confirm the age, but their study illustrates how diverse life was just a billion years after the planet formed.
“It’s not just finding this stuff that’s interesting,” says Alan Decho, a geobiologist at the University of South Carolina’s Arnold School of Public Health. “It’s showing that the life had some organization to it.” Ridges that crisscross the rocks like strands in a spider web hint that primitive bacteria linked up in sprawling networks. Like their modern counterparts, they may have lived in the equivalent of microbial cities that hosted thousands of kinds of bacteria, each specialized for a different task and communicating with the others via chemical signals.