Impact from the Deep - Scientific American

This is a featured article, positing that most of the major extinction events discovered by paleo-biology were not asteroid impacts but rather greenhouse type events engendered by oceanic gas releases. That a similar event might recur is a possibility, and another is that human gas releases put us on a similar trajectory.

Science & Technology at Scientific American.com: Impact from the Deep -- [ EARTH SCIENCE ] -- Strangling heat and gases emanating from the earth and sea, not asteroids, most likely caused several ancient mass extinctions. Could the same killer-greenhouse