STATE COLLEGE, Pa., March 1 (UPI) -- A U.S. study suggests an asteroid strike may not only have killed ocean and land life 65 million years ago, but it may also have caused extinction unevenness.
Researchers at Pennsylvania State University said such a fireball's strike might explain the geographic unevenness of extinctions and recovery.
Using samples from 17 Northern and Southern Hemispheres drilling sites, the scientists analyzed the community structure of calcareous, or shelled, nanoplankton. Included in their study were two sites -- one in the Pacific and one in the South Atlantic.
"At the Cretaceous-Paleogene boundary, 93 percent of the nanoplankton went extinct," said Professor Timothy Bralower, who led the project. "Nanoplankton are the base of the food chain in the ocean. If they go extinct, other, larger organisms that feed on them have problems."
Bralower, postdoctoral fellow Shijun Jiang, graduate student Jonathan Schueth and Associate Professor Mark Patzkowsky said they found the extinction level correlates with latitude. The highest rate of extinctions are in the Northern Hemisphere with decreasing extinction levels in the Southern Hemisphere.
A analysis of the asteroid that initiated the extinction event shows it came into our atmosphere in the southeast and traveled northwest, ultimately colliding with Earth on the tip of the Yucatan Peninsula in Mexico.
"This agrees with the fact that North American land plants were hammered and there was an especially sever mass extinction on that continent," Bralower.
The research is reported in the journal Nature Geoscience.
