From 220 million years ago until 65 million years ago, a vast number and changing variety of dinosaurs lived on Earth. Then, within a very short period of time, the dinosaurs became extinct.

The location of the Chicxulub Crater, on the Yucatan Peninsula, Mexico and the Deccan Traps in India.

Artist: Rodney Pike.

Source: Museum Victoria.

The debate about why this happened changed radically in 1980, when a high concentration of the rare metal iridium (often found in meteorites) was discovered in rocks at just the level where the dinosaurs became extinct. Deposits of iridium-rich clay have been found at the boundary of Cretaceous and Tertiary deposits (known as the K/T Boundary) in various parts of the world. Never before had something been tied so closely with that extinction event. Scientists hypothesised a collision of an asteroid some 10km in diameter with the Earth 65 million years ago. Since then, a large crater, Chicxulub, of just the right age to have been produced by the impact of such an asteroid has been found on the Yucatan Peninsula of Mexico.

On the other side of the world, at the time the dinosaurs went extinct, there was a vast outpouring of basalt in India, now called the Deccan Traps. Perhaps these two extreme events together were what started the chain of events that caused the dinosaurs to die out.

What the asteroid and volcanic activity did to the environment to bring about the extinction is still uncertain for not everything became extinct. The dinosaurs, large marine reptiles such as plesiosaurs and various marine inverterbrarates became extinct. Fish, crocodilians, turtles, birds, mammals and many invertebrates survived.