65,000,000 YEARS AGO
Dinosaurs Wiped Out in Asteroid Horror ?
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Did an asteroid striking Earth account for the demise of the prehistoric beast?
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About photography: The K/T boundary, the black layer between Cretaceous and Tertiary rock, is made from material ejected from an asteroid impact.
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“Having ruled the Earth for more than 100 million years, the dinosaurs suddenly died out 65 millions years ago.
So too did ammonites, most marine reptiles, many species of plankton, and many marsupials. Somehow, however, the small and primitive mammals survived, plus most species of bird, insect, lizard, and amphibian.
In some parts of world more than half of all plant species also became extinct.
What happened? Scientists have long debated how quickly the extinctions occurred — whether in the space of a few catastrophic years, or several millennia.
The most likely theories suggest one or several large asteroid impacts, which would have melted the Earth’s crust, causing massive atmospheric disruption and creating huge tsunamis and firestorms, followed by a drastic lowering of the sea level. One site now clearly identified with this is in the sea off the coast of Yucatan, which involved the impact of an asteroid 6 miles (10 km) in diameter. Its shape suggests that it hit at an angle, scattering much debris across North America.
The end of Cretaceous (K) and beginning of the Tertiary (T) period is known as the K/T boundary event. Yet it is not clear why some groups of animal were devastated whereas others survived. Smaller and burrowing animals were less affected than large surface dwellers, and free-swimming species suffered more than bottom feeding marine ones. But the survival of birds suggests that the atmospheric distributions may have been fairly short lived. (PF)
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