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The ten kilometre wide asteroid thought to have hit Chicxulub on the North Yucatan Peninsula, Mexico, produced an impact scar over 100 kilometres across. The impact threw up millions of tonnes of debris in to the atmosphere at velocities exceeding the planets escape velocity. The re-entering ejected matter would have caused a "heat pulse" around the globe, igniting fires and burning up all terrestrial organisms not sheltered in burrows or in water, states researcher Doug Robertson of the department of geological sciences at the University of Colorado, USA.
"The kinetic energy of the ejected matter would have dissipated as heat in the upper atmosphere during re-entry, enough heat to make the normally blue sky turn red-hot for hours," said Robertson. Scientists have speculated for more than a decade that the entire surface of the Earth would have been baked in the equivalent of a global oven. “The evidence of terrestrial ruin is compelling,” said Robertson, noting that tiny spheres of melted rock are found in the Cretaceous-Tertiary (KT) boundary around the globe. The spheres, found in clay layers, are remnants of the rocky masses that were vaporized and ejected by the impact.
“A nearly worldwide clay layer laced with soot and extra-terrestrial iridium also records the impact and global firestorm that followed the impact. The spheres, the heat pulse and the soot all have been known for some time, but their implications for survival of organisms on land had not been explained well,” said Robertson.
Many scientists have been curious about how any animal species such as primitive birds, mammals and amphibians managed to survive the global disaster that killed off all the existing dinosaurs. Robertson and colleagues have provided a new hypothesis for the differential pattern of survival among land vertebrates at the end of the Cretaceous. They have focused on the question of which groups of vertebrates were likely to have been sheltered underground or underwater at the time of the impact.
Their answer closely matches the observed patterns of survival. Pterosaurs and non-avian dinosaurs had no obvious adaptations for burrowing or swimming and became extinct. In contrast, the vertebrates that could burrow in holes or shelter in water, mammals, birds, crocodiles, snakes, lizards, turtles and amphibians, for the most part survived.
The paper was published in the May-June issue of the Bulletin of the Geological Society of America.
More info: University of Colorado
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