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Washington, March 2 (ANI): In a new research, scientists are studying tiny-shelled creatures called nannoplanktons to explain the geographic unevenness of extinctions and recovery 65 million years ago.

The researchers, using 823 samples from 17 drilling sites in both the Northern and Southern Hemispheres, analyzed the community structure of calcareous - shelled - nannoplankton.

Included in their study were two sites - one in the Pacific and one in the South Atlantic - with reliable, accurate dating.

“At the Cretaceous-Paleogene boundary, 93 percent of the nannoplankton went extinct,” said Timothy J. Bralower, head and professor of geosciences.

“Nannoplankton are the base of the food chain in the ocean. If they go extinct, other, larger organisms that feed on them have problems,” he added.

The researchers found that extinction level correlates with latitude.

The highest rate of extinctions is in the Northern Hemisphere with decreasing extinction levels in the Southern Hemisphere.

Analysis of the signature of the asteroid that initiated the extinction event shows that the asteroid came into our atmosphere in the southeast and traveled toward the 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,” said Bralower.

The initial dust and debris from the impact crater hit the Northern Hemisphere first and hardest.

Low-diversity opportunistic organisms that appear when other nannoplankton disappear persisted in the Northern Hemisphere for 40 thousand years after the impact and this hemisphere then took 270 thousand years to recover.

In the south, only intermediate levels of extinction occurred and greater diversity persisted, which agrees with the minor land plant changes in the Southern Hemisphere.

The darkness caused by the collision would impair photosynthesis and reduce nannoplankton reproduction.

While full darkness did not occur, the effects in the north would have lasted for up to six months.

However, with ample sunlight and large amounts of nutrients in the oceans, the populations should have bounced back, even in the North, but they did not.

The researchers suggest that toxic metals that where part of the asteroid, heavily contaminated the Northern oceans and were the major factor inhibiting recovery.

“Metal loading is a great potential mechanism to delay recovery,” said Bralower. “Toxic levels in the parts per billions of copper, nickel, cadmium and iron could have inhibited recovery,” he added. (ANI)