The Great Dying, which occurred approximately 252 million years ago, was the largest known mass extinction event on Earth, with the extinction of 57% of biological families, 83% of genera, 81% of marine species, and 70% of terrestrial vertebrate species. The precise causes of the Great Dying remain unknown, but scientists have proposed several mechanisms, including both catastrophic and gradual processes. Some of the proposed causes are:

• Flood basalt volcanic eruptions: The scientific consensus is that the main cause of extinction was the flood basalt volcanic eruptions that created the Siberian Traps, which released sulfur dioxide and carbon dioxide, resulting in euxinia and anoxia, elevating global temperatures, and acidifying the oceans.

• Global warming: New research shows that global warming caused by the flood basalt volcanic eruptions left ocean animals unable to breathe, which contributed to the mass extinction.

• Runaway greenhouse effect: The volcanic eruptions also caused a runaway greenhouse effect and ocean acidification, which wiped out 95% of both land and ocean species.

• Sulphide poisoning: The greenhouse effect led to vast deoxygenation and probably also sulphide poisoning of the oceans, killing the remaining organism groups.

• Environmental changes: The hotter climate shifted vegetation and ignited fires, which exposed more rocks, and erosion went into overdrive. As a result, an overabundance of nutrients flowed into the oceans, causing at first an explosion of life. But then there was the inevitable death and decomposition, which ate up most of the life-giving oxygen in the ocean.

In summary, the Great Dying was likely caused by a combination of factors, including volcanic eruptions, global warming, runaway greenhouse effect, sulphide poisoning, and environmental changes.