Kump claims that the carbon dioxide from the volcanic eruptions would have warmed the atmosphere, which would then have warmed the ocean's surface. The deep ocean normally gets oxygen from the atmosphere at the poles. Because the cold water there is dense, it sinks and slowly moves toward the equator, taking oxygen with it. The warmed ocean water would have allowed less oxygen to dissolve, and made the movement of oxygen toward the equator slower. Consistent with this hypothesis, researchers has shown that the deep oceans were anoxic in the late Permian, and the continental shelf areas in the end-Permian were also anoxic.

Without oxygen, less organic debris would have been aerobically consumed, which would have caused more carbon dioxide to appear in the atmosphere. The oceans would have become the realm of bacteria that obtain oxygen by stripping it from sulfur oxide compounds, which would have lead to the production of hydrogen sulfide. As the levels of oxygen in the atmosphere fell, while the levels of carbon dioxide and hydrogen sulfide rose, the upper levels of the ocean would have become so full of hydrogen sulfide that most oceanic plants and animals would have been killed. The hydrogen sulfide dispersed in the atmosphere would have killed most life on land.

Kump suggests that the movement of the ocean layers were not uniform, and that there were some places where oxygen remained on land and in the oceans. This would account for the survival of 5 percent of Earth’s species.