Asteroid impacts, climate change, volcanoes - there have been many theories about the causes of
mass extinctions. In some cases, such as the Cretaceous mass extinction event, more than one such
factor was involved in the global catastrophe.
Catastrophic methane release
Catastrophic methane release has been suggested as a possible cause of mass extinction. Methane clathrate is an ice-like substance formed from water and methane in the sea bed, arctic lakes and permafrost.
Flood basalt eruptions
Flood basalt eruptions are a type of large-scale volcanic activity, both in terms of extent and duration, that can occur on land or on the ocean floor. A flood basalt may continue to erupt for tens of thousands - possibly millions - of years and the lava can cover hundreds of thousands of kilometres.
Earth's climate is not constant. Over geological time, the Earth's dominant climate has gone from ice age to tropical heat and from steamy jungles to searing deserts.
Impact events, proposed as causes of mass extinction, are when the planet is struck by a comet or meteor large enough to create a huge shockwave felt around the globe. Widespread dust and debris rain down, disrupting the climate and causing extinction on a global, rather than local, scale.