Mare Crisium /ˈkrɪsiəm/ (Latin crisium, the “Sea of Crises”) is a lunar mare located in the Moon’s Crisium basin, just northeast of Mare Tranquillitatis. Mare Crisium is a basin of Nectarian age.
One of the most important events of the Proterozoic was the accumulation of oxygen in the Earth’s atmosphere.
Mare Crisium is just visible from Earth with the naked eye as a small dark spot on the edge of the Moon’s face.
