This is an extended technical paper published by the Geological Society of America. The authors are examining the pinching out of the Tethys Ocean during the assembly of Pangaea ~300 million years ago. Basically, it became a land-locked ocean being subducted under the continents on all sides, in what is now Asia and the Eastern Mediterranean. They analyzed extant sedimentary remnants from around the former basins from Turkey to Russia and Thailand, correlated the rate of anoxia (lack of oxygen) with water depth, showing that the oxygen went away over time from deepest basin to shallowest shelves, as it should. The modern Black Sea is highly anoxic at depth, preserving wooden ships from the time of ancient Greece, as nothing can live in such low oxygen levels. They also propose a spillway across Europe through Germany and Denmark which sloshed water back and forth between the shrinking Tethys and the global Panthallassa Sea. The conclusion of the book is that the life forms in the Tethys were stuck (or swam out while they could) and perished with their ocean, and the floor of the Panthallassa has been subducted away since then leaving a major gap in the fossil record. The Permian Extinction is assumed to be the largest extinction event known through fossils, something on the order of 90% of all families of life vanished. Still hazy. This is a complex work that I've barely touched on, really. Incredibly dense for a 60 page paper.