Chugging quietly away in the dark depths of Earth's ocean floors, a spontaneous chemical reaction is unobtrusively creating oxygen, all without the involvement of life.
This is really interesting, as it also has implications for life elsewhere in the solar system. Scientists have been debating back and forth whether life could exist in Europa's oceans below its icy surface. Things had been leaning towards "unlikely" due to the reduced light being that far out from the sun, but if non-photosynthetic biological oxygen production is possible on Earth, it could also be possible on Europa.