stylistic:tone, linguistic:paraphrasing, structural:summarization, information:classification, linguistic:voice_change
Hypotheses

Hypotheses to explain this gap must take into consideration the balance between oxygen sources and oxygen sinks. Oxygenic photosynthesis produces organic carbon that must be segregated from oxygen to allow oxygen accumulation in the surface environment, otherwise the oxygen back-reacts with the organic carbon and does not accumulate. The burial of organic carbon, sulfide, and minerals containing ferrous iron (Fe 2+) is a primary factor in oxygen accumulation. When organic carbon is buried without being oxidized, the oxygen is left in the atmosphere. In total, the burial of organic carbon and pyrite today creates 15.8 ± 3.3 Tmol (1 Tmol = 10 12 moles) of O per year. This creates a net O flux from the global oxygen sources.