1,800,000,000 Years Stromatolite
Example of Proterozoic algal matting. Layers, beds and reefs made of sun-loving slime lived for billions of years in shallow waters. When macro lifeforms evolved 600 million (or so) years ago, stromatolites became snail food. Today, stromatolites survive in hypersaline water such as the Hamelin Pool in Shark Bay, Australia. Fist-sized sample collected from the Pethei Formation, Blanchet Island, East Arm, Great Slave Lake, Northwest Territories, Canada.