The Great Zap! New Discoveries about the Permian Extinction of 90% of Earth's Species | Science News | Scoop.it
From www.dailygalaxy.com - November 21, 2011 7:47 AM
It was the greatest exinction event of all time (at least by Earth standards): Since the first organisms appeared on Earth approximately 3.8 billion years ago, life on the planet has had some close calls.