Artist's impression of the meteorite that killed the dinosaurs
Bang. And it all came to a sudden end. The dinosaurs went extinct, along with 50 to 70 percent of all other life. Or so the theory goes. This was the end Cretaceous extinction - the last major extinction event that has impacted on Planet Earth. Luis Alvarez, physicist and Noble Prize winner, and his geologist son Walter, discovered a layer of clay with 30 times higher levels of irridium than averge crustal content. This was back in the 1970's and in 1980 they published a scientific paper which put forward the theory that Earth had been hit by a massive meteorite that had thrown huge amounts of debris into the atmosphere which led to the rapid extinction of the dinosaurs.
If we were to have the same event now, it would have the same effect on all life, including us mammals. So what was this catastrophe that changed the Mesozoic world? The thinking was that a massive meteorite, approximately 10 km across, hit the Earth 66 million years ago and threw up vast quantities of dust and gas into the atmosphere, blocking out the sun which led to global cooling – an impact winter – that reduced the ability of plants and algae to photosynthesise. This may have been followed by a period of very high global temperatures, due to high CO2 levels in the atmosphere, which would have further stressed the surviving life forms which had previously been trying to adapt to the icy conditions.
Before this now widely accepted theory was put forward it was thought that the dinosaurs went extinct because they were stupid, slow moving and incapable of adapting to changes in their environment, and as a result were swept away by the more highly evolved, faster, cleverer mammals. It was thought of as a natural progression with humans perhaps being the final step in this progression. To this day we still use the expression “it is a real dinosaur” when speaking of something that is old and outdated. But the thinking about dinosaurs has changed a great deal since palaeontologists like John Ostrom, and perhaps more famously, Robert Bakker, began to challenge the idea that dinosaurs were slow and stupid.
Chicxulub Crater - the Smoking Gun of Dinosaur Extinction
In the early 1990s a massive impact crater was found in the Yucutan Peninsula off the coast of Mexico. Chicxulub was dated at 66 million years old which is the same age as that assigned to the K-Pg boundary. This date fitted the meteorite impact theory perfectly. The crater is buried under younger rocks but has been estimated at 180 km in diameter and 20 km deep, making it one of the largest confirmed impact craters on Earth. (South Africa has the largest and oldest crater at Vredefort).
Other events may have led to or assisted in driving the dinosaurs to extinction, including increased volcanic activity (Parana-Etendeka eruptions of Brazil -Namibia and the Deccan Traps eruptions in India), changes in sea level, changes in climate or perhaps a combination of all of the above.
See the other articles below for additional information on other extinction theories.
Dinosaur Extinction – The National Geographic View
Sixty-five million years ago the last of the non-avian dinosaurs went extinct. So too did the giant mosasaurs and plesiosaurs in the seas and the pterosaurs in the skies. Plankton, the base of the ocean food chain, took a hard hit. Many families of brachiopods and sea sponges disappeared. The remaining hard-shelled ammonites vanished. Shark diversity shriveled. Most vegetation withered. In all, more than half of the world's species were obliterated.
What caused this mass extinction that marks the end of the Cretaceous and the beginning of the Paleogene? Scientists have yet to find an answer. Read more>>>
New Dates Tie Volcanic Flood to Dinosaur Extinction
An incredible outpouring of lava 66 million years ago could have set off environmental changes that killed off the dinosaurs, a new study finds.
The research reports precise dates for India's Deccan Traps, mountain-high piles of basalt lava flows that cover as much territory as France. The youngest lava flows emerged 66.29 million years ago, about 250,000 years before the Chicxulub space rock crashed into eastern Mexico's Yucatan Peninsula. The findings could revive the idea that the Deccan Traps caused the Cretaceous-Paleogene extinction — a hypothesis long pushed aside in favor of the asteroid impact. Read more >>>