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Microbial mats show fossil structures from 3.5 billion years ago

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Pilbara home to 3.5 billion-year-old bacterial ecosystems From The Scientist :

In the Dresser Formation in Western Australia—one of the only places in the world with well-preserved 3.48-billion-year-old rocks—Nora Noffke of Old Dominion University in Norfolk, Virginia, and colleagues recorded microtextures characteristic of biofilms and microbial mats and uncovered geochemical signals consistent with a biological origin. The morphology and distribution of the fossils in this ancient coastal salt flat strongly resembled modern MISS.

Evidence suggests that the ancient biofilms behaved like modern microbes.

Abstract Microbially induced sedimentary structures (MISS) result from the response of microbial mats to physical sediment dynamics. MISS are cosmopolitan and found in many modern environments, including shelves, tidal flats, lagoons, riverine shores, lakes, interdune areas, and sabkhas. The structures record highly diverse communities of microbial mats and have been reported from numerous intervals in the geological record up to 3.2 billion years (Ga) old. This contribution describes a suite of MISS from some of the oldest well-preserved sedimentary rocks in the geological record, the early Archean (ca. 3.48 Ga) Dresser Formation, Western Australia. Outcrop mapping at the meter to millimeter scale defined five sub-environments characteristic of an ancient coastal sabkha. These sub-environments contain associations of distinct macroscopic and microscopic MISS. Macroscopic MISS include polygonal oscillation cracks and gas domes, erosional remnants and pockets, and mat chips. Microscopic MISS comprise tufts, sinoidal structures, and laminae fabrics; the microscopic laminae are composed of primary carbonaceous matter, pyrite, and hematite, plus trapped and bound grains. Identical suites of MISS occur in equivalent environmental settings through the entire subsequent history of Earth including the present time. This work extends the geological record of MISS by almost 300 million years. Complex mat-forming microbial communities likely existed almost 3.5 billion years ago. Key Words: Archean—Biofilms—Microbial mats—Early Earth—Evolution. Astrobiology 13, 1103–1124. – N. Noffke et al., “Microbially induced sedimentary structures recording an ancient ecosystem in the ca. 3.48 billion-year-old Dresser Formation, Pilbara, Western Australia,” Astrobiology, 13:1103-24, 2013.

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