Organic Matter Found in 3.5-Billion-Year-Old Stromatolites

Researchers have found exceptionally preserved organic matter inside samples of rock from the 3.5-billion-year-old Dresser Formation in the Pilbara region of Western Australia.

Baumgartner et al provide exceptional evidence for the biogenicity of some of Earth’s oldest stromatolites through preservation of organic matter, including microbial remains, by sulfidization. Image credit: Paul Harrison.

The Dresser Formation stromatolites have been thought to be of biogenic origin ever since they were discovered in the 1980s.

However, despite strong textural evidence, that theory was unproven for nearly four decades, because scientists hadn’t been able to show the definitive presence of preserved organic matter remains.

“This is an exciting discovery — for the first time, we’re able to show the world that these stromatolites are definitive evidence for the earliest life on Earth,” said Dr. Raphael Baumgartner, a researcher at the Australian Centre for Astrobiology at the University of New South Wales and the lead author of a paper published in the journal Geology.

“The discovery is the closest we have come to a ‘smoking gun’ to prove the existence of such ancient life,” said University of New South Wales Professor Martin Van Kranendonk, co-author of the study.

“This represents a major advance in our knowledge of these rocks, in the science of early life investigations generally, and — more specifically — in the search for life on Mars. We now have a new target and new methodology to search for ancient life traces.”

“These new pieces of critical evidence we have uncovered represent a truly exciting step forward, enabling us to prove the existence of ancient life on our planet,” said co-author Dr. Marco Fiorentini, from the University of Western Australia.

Stromatolites in the Dresser Formation are usually sourced from the rock surface, and are therefore highly weathered.

In the new study, the authors worked with samples that were taken from further down into the rock, below the weathering profile, where the stromatolites are exceptionally well preserved.

They analyzed the rocks using micro-analytical tools and techniques, including high-powered electron microscopy, spectroscopy and isotope analysis.

They found that the stromatolites are essentially composed of pyrite that contains organic matter.

“The organic matter that we found preserved within pyrite of the stromatolites is exciting — we’re looking at exceptionally preserved coherent filaments and strands that are typically remains of microbial biofilms,” Dr. Baumgartner said.

“The results obtained from the ongoing study at the Dresser Formation can be used as a blueprint to inform further research focusing on the analysis of Martian rocks, to ultimately search for clues of early life in the wider Solar System,” Dr. Fiorentini said.

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Raphael J. Baumgartner et al. Nano-porous pyrite and organic matter in 3.5-billion-year-old stromatolites record primordial life. Geology, published online September 25, 2019; doi: 10.1130/G46365.1