Up until this chapter, I have avoided discussion of what causes a mass extinction. Rather than a run-through of each mass extinction, I concentrate on two; the largest, the end-Permian; and the most controversial, the end-Cretaceous. Many (most) mass extinctions are linked to the environmental damage that results from the eruption of a Large Igneous Province (LIP) – that is certainly the case with both the end-Permian and end-Cretaceous. At the end of the Permian, the eruption of the Siberian Traps resulted in global warming and caused ocean waters to become both anoxic and acidic, resulting in the largest mass extinction seen on the planet.The situation of the end-Cretaceous is more complex. The eruption of the Deccan Traps placed significant environmental stress on the planet’s ecosystem which is recorded as shifts in the composition of the biota prior to the event. But the impact of a meteor is also involved in this extinction event, and it may have delivered the coup de grace.