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Hebrew stopped being regularly spoken sometime between 200 and 400 CE but remained in literary and religious use. In the 19th and 20th centuries, it was revived as an everyday spoken language on a large scale—an exceptionally rare case of a language returning to daily use after centuries.

Microbes were producing oxygen hundreds of millions of years before Earth's atmosphere became oxygen-rich. At first, much of that oxygen reacted with dissolved iron and other chemicals instead of accumulating in the air. Only after these chemical sinks could no longer consume oxygen as quickly as it was produced did atmospheric oxygen begin its major rise, around 2.4 billion years ago.