Dutch demonstrate dinosaur die-off

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Dutch geologists from the University of Utrecht and VU Amsterdam have discovered proof of a sudden cooling of the Earth directly after the impact of the asteroid in Mexico, which wiped dinosaurs from the world 66 million years ago, the Volkskrant reports. A dust cloud from the Chicxulub impact blocked out the sun for decades long. In the American journal PNAS Johan Vellekoop and colleagues show how the first years after that cosmic impact must have looked like. This time scale has generally been inconceivable in geological terms.

The scientists were able to reconstruct the temperature thanks to temperature-dependent chemical compounds in fossil alga discovered in sediment rock in Texas. At the time of the impact, this was still under water when the cosmic impact created a megatsunami in the Gulf of Mexico. The atmosphere was filled with dust and soot from fires.

In the 80s, Dutch Jan Smit from the VU Amsterdam was among other scientists who discovered indications for a colossal impact under the Mexican Yucatán peninsula at Chicxulub, which marks the extinction of the dinosaurs. A thin layer of iridium is traceable in rocks all over the earth. The old sea bed that now forms the riverbeds of the Brazos in Texas, was sufficiently deep and far away to remain relatively undisturbed. This means that powder and dust raining down landed in the water. "Actually our luck as geologists is that nothing much happened in this rock since the impact", says Vellekoop. "Closer to Chicxulub, the bed is geologically ravaged." Chemical readings of the rock shows that an unnatural winter set in quickly after the impact, lowering sea temperatures by at least 7 degrees, possibly more. Tropical conditions changed into the current winter temperatures during this 'impact winter'. In Texas, the iridium of the material that drifted down after the impact is easily recognizable, but it has been mixed with finer materials, from powder to clay. The researchers, including Jan Smit, think that this indicates that the sea bed has been stirred up over the decades. The structure of the petrified sediments also shows that there were heavy storms in the first decades after the impact, allowing the lad to cool off much quicker than the sea. After almost a century, a new equilibrium was struck in which the earth's oceans cooled by several degrees. The temperature in deeper waters is only expected to recover in several thousand years.

This cooling does not explain the mass extinction of dinosaurs, however, Vellekoop states. That was mainly caused by  the blackout of the sun from the dust, which lasted several years. Plants could not grow because photosynthesis was not possible. Herbivores therefore died out, leaving carnivores and omnivores hungry. The temperature also went down due to the blackout Paleontologist Robert Speijer with KU Leuven who is also researching in Texas, says he is impressed with the details of this study, which unravels the mysteries of the the dramatic event that killed off the world's dinosaurs 66 million years ago. "Months to years of darkness and cooling are realistic. The ecological impact must have been enormous."

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