Stromatolitic Limestone
“Stone layered by ancient microbes”
Stromatolitic limestone contains stromatolites — layered dome or column structures built by cyanobacteria (blue-green algae) that trap and bind sediment as they grow. These structures are among the oldest evidence of life on Earth, with some dating back 3.5 billion years.
calcite (microbially precipitated), micrite, dolomite (in older examples), silica (chert replacement), organic carbon
Shark Bay (Western Australia — living stromatolites), Pilbara (Western Australia — 3.5 Ga fossils), Glacier National Park (USA), Brazil, South Africa
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Living stromatolites at Shark Bay, Australia are among the rarest ecosystems on Earth — they thrive only because the hypersaline water keeps grazing animals away, preserving a window into how life looked for most of Earth's history.
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What role did stromatolite-building cyanobacteria play in transforming Earth's early atmosphere?
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