The end-Permian crisis, by far the most dramatic biological crisis to affect life on Earth, was triggered by a number of physical environmental shocks -- global warming, acid rain, ocean acidification and ocean anoxia. These were enough to kill off 90 per cent of living things on land and in the sea.
MORE: http://www.sciencedaily.com/releases/2012/05/120527153810.htm
See also...
Mars 'has life's building blocks'
http://www.bbc.co.uk/news/science-environment-18196353
