Asteroid strike at K/T boundary

Science Daily March 1st (www.sciencedaily.com id100301102805) an asteroid strike at the K/T boundary may account for geographic uneveness of the extinctions and recovery according to research by Penn State University geoscientists. At the Cretaceous-Paleogene boundary 93 per cent of nanno plankton became extinct – and these are basic to the ocean food chain. The highest rate of extinction was in the northern hemisphere with decreasing levels in the southern hemisphere. The asteroid appears to have entered earth’s atmosphere from the SE and travelled towards the NW – colliding with the earth at the tip of the Yucatan peninsular. North American land plants disappeared and there is plenty of evidence of mass extinction in the region. In contrast, in the south, only intermediate levels of extinction occurred and greater diversity persisted. However, the darkness caused by the collision would have impaired photo-synthesis. The authors did not address the controversial geology.