Robert Broughton (UK).
The end Permian mass extinction occurred 251mya and marked the end of the Palaeozoic era. The loss of life is currently estimated to consist of 95% of the marine fauna and around 70 to 77% of the known terrestrial fauna (where the fossil record is inevitably less complete). This article will provide an overview of the many events and processes that played a part and a discussion whether they can all be attributed to a single, root cause.
At this time, the landmass was united into the single, super-continent of Pangea, surrounded by warm shallow seas with abundant reef systems. This extensive reef fauna supported a variety of suspension feeders (for example, crinoids, rugose and tabulate corals, and so on), which were the most heavily hit by the extinction event, with all the known corals dying out. Modern scleractinian corals only appeared in the Triassic and there is a considerable gap in the coral fossil record at this time. Other reef inhabitants, such as the last phillipsid trilobites also became extinct. All these creatures were sessile or relatively immobile inhabitants of the reefs that occupied a relatively narrow zone on the continental shelf. This habitat must have been destroyed almost globally by a number of factors, but importantly, the single shelf margin around Pangea meant there was no other shallow reef environment for the fauna to migrate to.
The single continent of Pangea was always doomed to split apart. Rock is a great insulator of heat and the thick mass of continental crust allowed heat to build up in the mantle. Eventually, this upwelling of heat would have had a ‘blow torch’ affect and the continent rifted apart. Today, this process can be seen along East Africa’s Rift Valley. Two hundred and fifty one million years ago, it was Pangea’s turn. It is suggested that a hotspot under present-day Siberia caused the initial fracturing, which released huge quantities of fluid, flood-basalt lavas. Because all landmasses were united into a single continent, there were no controls or limits on the radiating fracture systems that would propagate outwards from the initial epicentre. The resulting eruption lasted about one million years and three million cubic kilometres (about 1,860,000 cubic miles) of basalt flooded the Earth’s surface.