Massive Fluctuation in Oxygen Levels were a part of it

And the waters prevailed, and were increased greatly upon the earth; and the ark went upon the face of the waters. Genesis 7:18

"The Permian-Triassic extinction event .....was so severe that it's often called the Great Dying.

 .....a new study offers some intriguing extra detail on the calamity: a sudden spike in oxygen levels in the world's oceans at the same time as this widespread extinction was happening.....the sudden burst of oceanic oxygenation occurred around the start of the Great Dying.

Without the aid of a time machine, measuring oxygen levels in the ocean eons ago isn't easy, but the team analyzed thallium isotopes buried in ocean sediments as a way of estimating the chemical mix of seawater....

---observed a slow reduction in ocean oxygen levels – technically known as ocean anoxia – across the course of the Permian–Triassic extinction event, 

---but this earlier spike in oxygenation hasn't been seen before.

The next question is what caused it and what it means. It could be possible that a rise and then sudden fall in ocean oxygen levels is more dangerous for marine species than a more gradual decline, the researchers suggest. "We were surprised to see this really rapid oxygenation event coinciding with the start of the extinction and then a return to reducing conditions."

An intense injection of carbon dioxide into the atmosphere is likely to have brought about the Great Dying, scientists think, quite possibly originating from Siberian volcanic activity across a vast scale." ScienceAlert