The SECOND mass extinction wasn’t just one event, but were actually two distinct events that we have conflated into one. Separately, they are known as the Kellwasser Event and the Hangenberg Event and happened about 13 million years apart from each other. It is debated what the main cause of these extinctions were caused by, whether that was anoxia (aka. oxygen deprivation in the ocean) from extreme algae growth, global cooling, or a volcanic supereruption.