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Remnants Of Complex Ecosystem Found In A 3.5 Billion-Year-Old Sedimentary Rock Sequence In Australia

November 13, 2013
Image Caption: A rock surface is displaying "polygonal oscillation cracks" in the 3.48 billion-year-old Dresser Formation in the Pilbara region of Western Australia. These similar sedimentary structures are of biological origin. They document ancient microorganisms that formed carpet-like microbial mats on the former sediment surface. The Dresser Formation records an ancient playa-like setting. Credit: Nora Noffke

April Flowers for redOrbit.com – Your Universe Online

Scientists trying to reconstruct the rise of life during the period of Earth’s history when it first evolved find the task daunting because the planet’s oldest sedimentary rocks are not only rare, but nearly always altered by hydrothermal and tectonic activity. A new study, published in the journal Astrobiology, reveals the well-preserved remnants of a complex ecosystem in a nearly 3.5 billion-year-old sedimentary rock sequence in Australia.

Western Australia’s Pilbara district constitutes one of the famous geological regions that allow insight into the early evolution of life. Ancient photosynthetic bacteria, known as stromatolites, created mound-like deposits that have been previously described, along with microfossils of bacteria, in detail. The previous studies of this region, however, made no mention of a phenomenon called microbially induced sedimentary structures, or MISS. MISS structures are formed from mats of microbial material, which resemble mats seen today in stagnant waters or in coastal flats.

The team, which included Nora Noffke, Associate Professor at Old Dominion University and visiting professor at Carnegie Institution for Science, PhD student Daniel Christian of Old Dominion University, and David Wacey of the University of Western Australia, described various MISS preserved in the region’s Dresser Formation. Advanced chemical analyses point toward a biological origin of the material.

The MISS fossils in the Dresser formation strongly resemble the MISS from several other younger rock samples in both form and preservation, such as, for example, a 2.9 million year old ecosystem Noffke and her colleagues found in South Africa .

“This work extends the geological record of MISS by almost 300 million years,” said Noffke. “Complex mat-forming microbial communities likely existed almost 3.5 billion years ago.”

According to the study, the sedimentary structures arose from the interactions 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.

Mars rovers are also searching for MISS formations on the red planet, meaning that the team’s findings could have implications for studies of our larger Solar System as well.


Source: April Flowers for redOrbit.com - Your Universe Online



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