Paleontologists hypothesize many mechanisms by which mass extinctions on Earth could have occurred, not all of which can be true. However, it is fun to speculate other planets in which a given theory has occurred. Create a hard science fiction show based on the premise of witnessing these interesting events, rare coincidences of various biological, geological, and physical forces. Even though the exact conditions of a hypothesis may not have occurred on Earth, it is plausible that they have occurred somewhere in the universe. (Your standard disaster / end-of-the-world flick, except grounded in science.)
Inspired by a scenario of catastrophic degassing of carbon dioxide from the deep global ocean described below.
Tracking the Course of Evolution
However, after about 255 Ma the radiolarians become rarer toward the P-Tr boundary, and across the boundary there are none at all, suggesting that Panthalassa became anoxic right to the surface. Long after the extinction, around 245 Ma, the surface waters again became oxygenated enough to support radiolarians, but the deep waters were anoxic until about 240 Ma.
If Panthalassa became anoxic right to the surface, this in itself would cause a catastrophic extinction of marine organisms.
Andrew Knoll and his colleagues have suggested that the extinction was caused by a catastrophic overturn of an ocean supersaturated in carbon dioxide. This would result in tremendous, close to instantaneous, degassing that would roll a cloud of (dense) carbon dioxide over the ocean surface and low-lying coastal areas. An analog might be the recent catastrophic degassing of Lake Nyos, in the Cameroon, where hundreds of people were killed as carbon dioxide degassed from a volcanic lake and cascaded down valleys nearby. The difference is that the proposed P-Tr disaster was global.
In this scenario, the carbon dioxide build-up results from the global geography that included the gigantic ocean Panthalassa. Knoll and colleagues speculated that the abnormal ocean circulation in Panthalassa did not include enough downward transport of oxygenated surface water to keep the deep water oxygenated.