Complex Bacterial Ecosystem Preserved in Stone for 3.5 Billion Years

A complex bacterial ecosystem has been found preserved in a 3.5 billion-year-old sedimentary rock sequence in Australia.

The find is a rare one, according to the research team behind a study of the rock sequence published in the journal Astrobiology, because most rocks that old have almost always been altered by hydrothermal or tectonic activity.

The rare rock sample was unearthed in the Pilbara district of Western Australia, a place known for harboring significantly old rock. The rock has entombed a rare phenomenon called microbially induced sedimentary structures, or MISS, that has not previously been documented in rocks from the Pilbara region.

The research team has described various MISS examples preserved in the region's Dresser formation. MISS are formed by mats of microbial material, much like mats seen in stagnant water and coastal flats today. The Dresser MISS samples are similar in form and preservation to MISS samples from several other younger rock samples, such as a 2.9 billion-year-old sample found in South Africa by a member of the same research team that uncovered the Dresser samples.

"This work extends the geological record of MISS by almost 300 million years," said Nora Noffke of the Carnegie Institution, who is also a professor at Old Dominion University. "Complex mat-forming microbial communities likely existed almost 3.5 billion years ago."

Noffke and her colleagues have proposed that the MISS formed through the interaction of bacterial films with shoreline sediments from the region.

"The structures give a very clear signal on what the ancient conditions were, and what the bacteria composing the biofilms were able to do," Noffke said.

The find may also prove valuable to research taking place in another part of the solar system. The Mars rovers are also, incidentally, scouring the Red Planet for MISS samples as well.