The Mesoarchean (//, also spelled Mesoarchaean) is a geologic era within the Archean Eon, spanning 3,200 to 2,800 million years ago. The era is defined chronometrically and is not referenced to a specific level in a rock section on Earth. Fossils from Australia show that stromatolites have grown on Earth since the Mesoarchean. The Pongola glaciation occurred around 2,900 million years ago. The first supercontinent Vaalbara broke up during this era about 2,800 million years ago.
3200–2800 million years ago
The earliest reefs date from this era, and were probably formed by stromatolites. Analysis of oxygen isotopes in cherts led to an oceanic temperature estimate around 55-85º C , while other studies of weathering rates postulate average temperatures below 50º C. Dinitrogen content in the atmosphere is thought to have been fundamentally similar to today's, and the partial pressure of carbon dioxide was probably lower than 0.7 bar.
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