Precambrian

The span of Earth history from its formation about 4.54 billion years ago to the beginning of the Cambrian Period roughly 539 million years ago. It includes the Hadean, Archean, and Proterozoic eons.

Hadean: The earliest eon of Earth history, beginning with Earth’s formation and ending about four billion years ago. It covers the Precambrian’s opening interval, when Earth and the Moon formed.
Moon formation: The origin of Earth’s natural satellite, generally explained by a giant impact early in Solar System history. The leading model connects the Moon’s formation to a major event in the Hadean.
Acasta Gneiss: A group of ancient rocks in Canada, with ages reaching about 4.03 billion years. It provides some of the oldest known surviving evidence of Earth’s crust.
Origin of life: The set of scientific questions about how life first arose from nonliving matter. Precambrian rocks may preserve clues, but the transition itself is not known.
Cambrian explosion: A geologically rapid diversification of animal life beginning around 539 million years ago. It followed the Precambrian and made animal fossils far more prominent.
Archean: An eon of Earth history from about four billion to 2.5 billion years ago. It follows the Hadean and contains the earliest widely accepted evidence of life.
Plate tectonics: The movement and interaction of large rigid plates that make up Earth’s outer shell. Its early history shaped continents, oceans, and the recycling of surface materials.
Strelley Pool Chert: An approximately 3.43-billion-year-old rock formation in Western Australia containing evidence interpreted as early life. Its structures and chemistry are central to debates about Archean organisms.
Earliest known life: The oldest proposed evidence of living organisms, identified from ancient geological and chemical traces. Claims about its age depend on interpreting structures and chemical signatures in Precambrian rocks.
Eukaryote: An organism whose cells contain a nucleus and other membrane-bound compartments. Eukaryotes arose during the Proterozoic, before complex animals became widespread.

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