Fossil

Stromatolites first appeared in the fossil record during the Archean Eon, 3,481,000,000 years ago. That's 3.4 billion years, nearly two-thirds of Earth's existence. Photosynthetic cyanobacteria living in shallow pools of water formed large colonies, taking in light and carbon dioxide and producing mucus and calcium carbonate. Each layer of the microbial mat built upon the last, forming an intricate laminate structure, growing into fascinating patterns of limestone that would stand through the ages as evidence of the lives of these microscopic organisms.