The extinction
Although the fossils of dinosaurs during the entire mesozoic era suggest a high diversity of organisms adapted to a variety of habitats, the reason for their final wholesale extinction some 65 million years ago is not completely resolved. However, this extinction does correlate with a thin band of iridium-enriched clay that marks the boundary between Cretaceous and Tertiary periods (nicknamed the K-T boundary). Because iridium is rare on earth, but common in meteorites, it was proposed that the earth was hit by an asteroid 10 km in size. More recently proof of such a meteorite has been found in the Gulf of Mexico (off the continental shelf of the Yucatan Peninsula). This impact site has formed the Chicxulub crater. To have formed this crater the meteorite would have needed to be at least 10 km in diameter. The impact of such a meteorite would have caused massive impact earthquakes, perhaps hundreds of times greater than the largest measured earthquake. Massive tsunami waves (tidal waves) would have radiated out.
Chicxulub Crater
Radar topography reveals the 180 kilometer (112 mile) wide ring of the crater (image courtesy NASA/JPL-Caltech)
When such a meteorite struck the earth, dust would have blanketed the globe, darkness would have occurred for one to three months and land temperatures would have plummeted. Since the meteorite very likely hit the sea, the water vapour could have created a greenhouse effect, making the short-term climate exceptionally hot, although in the long-term the temperature declined. Hot nitric acid would have rained out of the atmosphere and threatened many organisms with death, particularly those possessing shells. Recent evidence of large amounts of soot in the K-T sediments suggest that large-scale fires accompanied such a catastrophe (as much as 90% of the world's forests may have burned). Such events would have had a profound effect on the ecosystems of the world.
Badlands near Drumheller, Alberta where erosion has exposed the KT boundary.
