The Neoarchean ( ; also spelled Neoarchaean) is the last geologic era in the Archean Eon that spans from 2800 to 2500 million years ago—the period being defined chronometrically and not referencing a specific level in a rock section on Earth. The era is marked by major developments in complex life and continental formation.
Complex life
left|thumb|[[Semi-log plot|Semi-logarithmic graph showing the increase of oxygen in Earth's atmosphere through Earth's geological history]]
This era saw the rise of oxygen in the atmosphere after oxygenic photosynthesis evolved in cyanobacteria as early as the Mesoarchean era. The environmental changes that occurred in the Neoarchean such as its developing atmospheric and soil compositions drastically differentiated the era from others in its encouragement of microbial metabolisms to evolve and diversify. The era could have also seen pre-biotic organic molecules being brought to Earth through meteorites, comets, or through abiotic reactions. The growth of juvenile continental crust as well as the onset of plate tectonics in the Archean allowed for the colonization of a larger variety of niches by microorganisms through increasing the number of rock types present and thereby increasing the surface's chemical diversity.
The earliest potential eukaryote fossils come from Neoarchaean deposits in South Africa dating to 2.8 to 2.7 Ga, resembling present day siphonalean microalgae. However, the identity of these microfossils as eukaryotes is highly controversial and remains disputed.
Continental formation
During this era, the supercontinent Kenorland is proposed to have formed about 2.7 billion years ago. Kenorland is of particular interest due to it containing deposits of volcanic-hosted massive sulphide, gold, and uranium found in the Canadian Shield. With new research, the validity of Kenorland has been questioned in favor of other Neoarchean supercontinent proposals Superia or Vaalbara.