In his October 2006 Scientific American article, Impact from the Deep(1), Peter Ward argues that our planet's ancient mass extinctions were caused, not by asteroid impacts, but by hydrogen sulphide eruptions from the sea due to global warming. According to Ward, we may be at the doorstep of yet another extinction -- this time our own. Read more at sciam.com(2).

1. http://www.sciam.com/article.cfm?articleID=00037A5D-A938-150E-A93883414B7F0000&pageNumber=1&catID=2
2. http://www.sciam.com/article.cfm?articleID=00037A5D-A938-150E-A93883414B7F0000&pageNumber=1&catID=2