Knowra Earliest known life forms Earliest known life forms The oldest organisms or traces of organisms identified in Earth’s geological record. Their ages and biological origins remain debated because ancient rocks are altered and evidence can resemble nonbiological structures.
Isua greenstone belt : A region of ancient metamorphic rocks in southwest Greenland, including some of Earth’s oldest preserved crust. Its carbon isotopes have been interpreted as evidence of life more than 3.7 billion years ago.
Stromatolite : A layered sedimentary structure commonly formed as microbial communities trap or bind sediment and promote mineral precipitation. Ancient examples may record microbial mats, although nonbiological processes can produce similar layers.
Archean : A geologic eon lasting from about 4.0 to 2.5 billion years ago, when Earth’s earliest widely accepted rocks formed. Most candidate records of Earth’s earliest life come from Archean rocks.
Origin of life : The set of scientific questions about how living systems first arose from nonliving matter on Earth or elsewhere. The oldest known evidence postdates life’s actual beginning, whose timing and pathway remain unknown.
Nuvvuagittuq Greenstone Belt : An ancient, metamorphosed volcanic-rock formation on Quebec’s eastern shore of Hudson Bay. Its disputed age and possible microbial structures make it a candidate for Earth’s oldest biosignatures.
Microfossil : A fossilized microscopic organism or part of one, preserved in rock or sediment. The oldest proposed cellular fossils are microscopic and can be difficult to distinguish from mineral structures.
Geologic time scale : A system for organizing Earth’s history into eons, eras, periods, and epochs. It places proposed ancient fossils within the long interval before abundant, diverse life appears.
Abiogenesis : The emergence of living systems from nonliving chemical precursors. It concerns the transition that must precede any organisms represented in Earth’s geological record.
Pilbara Craton : A region of ancient continental crust in Western Australia that preserves rocks from the Archean Eon. Its stromatolites and other structures document candidate microbial ecosystems around 3.5 billion years ago.
Biosignature : A chemical, structural, or isotopic feature that may indicate past or present life. Claims for ancient life depend on whether geological features can be reliably attributed to biology.
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