Nickel-eating bacteria may have worsened the mass die-off some 250 million years ago, scientists suggest. (Shown here, International Space Station astronaut Ron Garan captures one of the 16 sunrises ... more 

Nickel-eating bacteria may have worsened the mass die-off some 250 million years ago, scientists suggest. (Shown here, International Space Station astronaut Ron Garan captures one of the 16 sunrises they see each day, on Aug. 27, 2011.) less