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The Neoarchean (pron.: /ˌniː.oʊ.ɑrˈkiː.ən/; also spelled Neoarchaean) is a geologic era within the Archaean. It spans the period of time from 2,800 to 2,500 million years ago—the period being defined chronometrically and not referenced to a specific level in a rock section on Earth. Oxygenic photosynthesis first evolved in this era and was accountable for the oxygen catastrophe which was to happen later in the Paleoproterozoic from a poisonous buildup of oxygen in the atmosphere, produced by these oxygen producing photoautotrophs, which evolved earlier in the Neoarchean. The supercontinent Kenorland formed during this period, about 2,700 million years ago.