Statherian

The Statherian ( ; Ancient Greek: σταθερός, romanized: statherós, meaning "stable, firm") is the fourth and final geologic period in the Paleoproterozoic Era, lasting from 1800 to 1600 million years ago (Ma) and spanning 200 million years. It follows the Orosirian Period and precedes the Calymmian Period, with the latter belonging to the Mesoproterozoic Era. Instead of being based on stratigraphy, these dates are defined chronometrically. The period was characterized on most continents by either new platforms or final cratonization of fold belts. Oxygen levels were 10% to 20% of current values. Rafatazmia, controversially claimed to be present in Statherian beds in India, may be the oldest known confirmably eukaryotic fossil organism. By the beginning of the Statherian, the supercontinent Columbia had assembled. Approximately 1.7 billion years ago, natural nuclear fission reactors were generating power in what is now Oklo, Gabon.