There are many causes of extinction; here are examples of some:
- 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 kilometers.
- Climate change- 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- 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 shock wave felt around the globe. Widespread dust and debris rain down, disrupting the climate and causing extinction on a global, rather than local, scale.
- Spread of Invasive Species- Invasive species invade foreign territory. They use resources that the other species depend on. Once competition gets too great, the survival of the fittest plan will begin, and one of the species, usually the natural one, will die off.
- Disease/Epidemic- Each species has defense mechanisms, such as their immune system and the ability to fight disease. With the changing climate and landscape certain species are losing their ability to fend off disease. They are becoming more susceptible to disease and epidemics, which can lead to their eventual extinction.
- Acid Rain- Acid rain forms when sulfur dioxide and/or nitrogen oxides are put out into the atmosphere. The chemicals get absorbed by water droplets in the clouds, and eventually fall to the earth as acid precipitation. Acid rain increases the acidity of the soil which affects plant life. It can also disturb rivers and lakes to a possibly lethal level.
Here is a video on the effects on extinction.