Permian / Triassic (~255 Ma)
- ~70% of species died
- Flood Basalts, black schists
- massive drop in O2
- Pangaea was finally formed
- the Variscan Orogen ended with the formation of the Ural mountains
The biggest of the Big 5 Events of Mass Extinction took place in the end of Permian. To be exact, it were two events that lasted for the duration between the ages of Guadalupian and Induan, both lasted about 100 Ma each. This time the main victims were big vertebrates, plants with a high biomass and highly-calcifying organisms. To name some orders, it was the end for Fusinilida, Tabulata and Rugosa corals, Trilobites and Eurypterids. Brachiopods, Bryzoa, Crinoids and plenty of other groups were depleted.
Ammonite (Goniatitic) and Trilobite
During Carboniferous and Permian earth was rich in atmospheric oxigen, which changes immensely towards the end of Permian. The oxigen content dropped by 20% from 35% to 15% (today it’s around 20%). Some organisms could adapt to this content, so a more or less sudden drop has fatal consequences and may easily lead to death.
The main reason for these changes may be a high volcanic activism. Flood basalts document a state of high lava flow. Besides that they build wonderful geologic structures that can be marvelled at in India (see Deccan Traps, these are from the K/T boundary though). But flood basalts also have the bad feature to set free amounts of methan and sulfur that lead to anoxic conditions in ocean water.
Volcanism can always be interpreted as the cause of two very different effects. Either it sets free too much carbondioxid and heats up the earth or there’s so much ash and dust in the air that the albedo rises and earth cools down. Scientists seem to choose the effect that fits their beliefs best. Nevertheless, volcanism is an important factor in the Permian Extinction Event.
Rocks from that time are black schists and you can also find evaporites from the Zechstein sea. By the end of Permian there is a mushroom peak, meaning there were way more mushrooms living on earth than before. It’s possible that bacteria set free halocarbon to the atmosphere which damages the ozon layer as well as plants.
As you can see, an Extinction is a complex event that cannot be explained by saying “This is the cause, that was the result.”, but there are many factors to it.