Scientists studying geological structures in Australia have found evidence of microbial life in 3.48 billion-year-old rocks. Their discovery could represent the oldest biosignatures yet identified on Earth.

Nora Noffke of Old Dominion University first spotted what looked like a microbially-induced sedimentary structure (or MISS) while visiting Australia in 2008. The MISS structures were found in Western Australia’s Dresser Formation, which contains some of the oldest known rocks on Earth’s surface. The Dresser Formation is an active research site for scientists studying the ancient environment of Earth, but the MISS structures had not been spotted before.

With support from the NASA Exobiology Program and the NASA Astrobiology Institute, Noffke and her team returned to the Dresser Formation in order to determine whether or not the structures were truly biological in origin. The results of the study were published in the journal Astrobiology

Studying MISS structures can help scientists understand what the environment of early Earth was like, providing clues about the origin and evolution of Earth’s biosphere. The structures could also help guide the search for ancient biosignatures on planets like Mars.