How did the burial of organic carbon increase atmospheric oxygen?

The burial of organic carbon is a critical process in the evolution of the atmosphere because it prevents the reoxidation of organic matter, thereby allowing oxygen to accumulate in the atmosphere.12

Through photosynthesis, organisms convert carbon dioxide and water into organic compounds and molecular oxygen ($O_2$). Under normal conditions, when these organisms die, they undergo respiration or decomposition, a process that consumes oxygen and releases carbon dioxide back into the atmosphere, effectively recycling the carbon.3415

However, when organic matter is buried in sedimentary rocks and protected from decomposition, the oxygen produced during its initial creation is not consumed by the decay process. Because this organic carbon is effectively removed from the biological cycle, the corresponding oxygen remains in the atmosphere. Over geologic time, this persistent imbalance—where production by photosynthesis exceeds consumption by respiration—has been a primary driver in raising atmospheric oxygen levels.152