Stromatolite

A layered sedimentary structure formed as microbial communities trap sediment or promote mineral precipitation. Ancient stromatolites preserve evidence of some of Earth’s earliest known ecosystems.

Microbial mat: A surface-associated community of microorganisms embedded in a cohesive layer of extracellular material. Stromatolites can grow as microbial mats bind sediment or induce mineral formation.
Archean: A geological eon spanning approximately 4.0 to 2.5 billion years ago. Many of the oldest widely accepted stromatolites date to the Archean.
Shark Bay stromatolites: Modern stromatolites growing in hypersaline waters at Shark Bay, Western Australia. They are a prominent living example of stromatolite growth in an unusual modern environment.
Thrombolite: A microbialite with clotted internal fabric rather than distinct, regular lamination. Thrombolites are commonly compared with stromatolites because both can form through microbial activity.
Microbialite: A sedimentary deposit whose formation is influenced by microorganisms. Stromatolites are layered structures within this broader class of microbial deposits.
Dresser Formation: A geological formation in Western Australia containing some of Earth’s oldest known stromatolites. Its approximately 3.48-billion-year-old structures are central evidence for early stromatolite formation.
Cayman stromatolites: Modern stromatolites found in marine settings around the Cayman Islands. Their occurrence shows that modern stromatolite growth is not limited to hypersaline bays.
Oncolite: A rounded, concentrically layered carbonate grain formed around a nucleus, often with microbial influence. Unlike attached stromatolitic buildups, oncolites typically grow as mobile coated grains.
Carbonate precipitation: The formation of solid carbonate minerals from dissolved ions in water. Microbial activity can promote carbonate precipitation that cements stromatolite layers.
Isua greenstone belt: A region of southwestern Greenland containing some of Earth’s oldest exposed rocks. Claims of ancient stromatolites here illustrate the difficulty of identifying biological structures in old rocks.

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