Extinction and Recovery 65 Million Years Ago
An asteroid could not only explain the disappearance of the oceans and land life 65 million years, but towards the fireball and the resulting dust, darkness and toxic metal contamination can explain the geographic differences of extinction and recovery, according to Penn State geoscientist.
“Our results shed light on the causes of extinction nanoplankton, how was restored productivity, the factors controlling the origin of new species, and, finally, how phytoplankton influence the restoration of the entire marine ecosystem, researchers report in this month’s issue of Nature Geoscience.
The researchers, using 823 samples from 17 drill sites in both northern and southern hemispheres, analyzed the community structure of limestone – shelled – nanoplankton. Included in the study were two places – one in the Pacific and one in the South Atlantic – with reliable, accurate dating.
“In the Cretaceous-Paleogene, 93 percent of the nanoplankton were extinct,” said Timothy J. Bralower, director and professor of earth sciences. “Nanoplankton are the foundation of the food chain in the ocean. If extinct, other larger organisms that feed on them have problems.”
Scientists have collected large amounts of data in nanoplankton from this time period, but according to Bralower, each sample was analyzed separately, and no one is compiled separate sampling results. Bralower, in collaboration with Jiang Shijun, a postdoctoral fellow now at Florida State University and Mark E. Patzkowsky, associate professor of earth sciences, Lee R. Kump, professor of earth sciences, and Jonathan D. Schueth, a graduate student in earth sciences, all at Penn State, found that the level of extinction is correlated with latitude. The highest rate of extinction is in the northern hemisphere with decreased levels of extinction in the Southern Hemisphere.
Analysis of the signing of the asteroid that initiated the extinction event shows that the asteroid came to our atmosphere, in the southeast and northwest traveled ultimately collide with Earth on the tip of the Yucatan Peninsula in Mexico.
“This is consistent with the fact that land plants in North America were negotiated and there was a mass extinction, especially cut to that continent,” Bralower said.
The initial dust and debris from the impact crater the Northern Hemisphere hit first and hardest. Under the range of opportunistic organisms that appear when others disappear nanoplankton persisted in the Northern Hemisphere for 40 thousand years after the impact of this hemisphere and then took 270 thousand years to recover. In the south, only intermediate levels of extinction occurred and greater diversity persists, which agrees with the changes minor plant the land in the southern hemisphere.
The darkness caused by the collision could affect photosynthesis and reduce reproduction nanoplankton. While there was total darkness, the effects in the north, would have lasted up to six months. However, with broad sunlight and a large amount of nutrients in the oceans, populations have recovered, even in the North, but did not. The researchers suggest that if toxic metals from the asteroids, heavily polluted northern oceans and were the main factor inhibiting recovery.
The “burden of metal is a great potential mechanism for delaying the recovery,” Bralower said. “Toxic levels in parts per billion of copper, nickel, cadmium and iron could have hampered the recovery.”
On the one hand, researchers consider a scenario of impact that causes the perpetual winter and acidification of the oceans to explain the slow recovery, but does not explain the gap between northern and southern hemispheres. Trace metal poisoning, by contrast, would have been serious about the impact on the Northern Hemisphere. When high-temperature waste of the consequences of falling into water, copper, chromium, aluminum, mercury and lead are dissolved in seawater to potential lethal levels for plankton. Iron, zinc and manganese – usually micronutrients – to reach unhealthy levels shortly after the impact. Other sources of metals can be leached soils acid rain and effects of forest fires. Metals such as these can inhibit the reproduction or formation of shell.
Toxic metals, probably exceeded the capacity of organic compounds that bind and remove them from the system. Because nanoplankton are the base of the food chain, larger organisms are concentrated all metals are found in nanoplankton make more efficient metal poisoning. With the other toxic metals in the oceans and the lack of sunlight, length of recovery time could increase.
“We still do not really know why some things that die, while others hang by a very small budget, and finally the recovery,” Bralower said.
NASA’s Exobiology supported this research and drilling samples came from the National Science Foundation Integrated Ocean Drilling Program.
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