02. Why did the dinosaurs die out?
Asteroids are planetary bodies or objects that revolve around the Sun. Most are in the asteroid belt between Mars and Jupiter. Meteorites are lumps of stony or metallic material that were parts of asteroids. They survive entering the Earth’s atmosphere and impact on the Earth’s surface. The Alvarez hypothesis suggests the mass extinction of the dinosaurs was caused by an impact of a large meteorite on the earth about 65 million years ago.
What evidence do scientists have for this?
In Italy, between Rome and Florence, scientists found fossils in limestone rocks that date back to when the dinosaurs died out. Near these rocks is a layer of clay containing high levels of iridium. Iridium is a very rare metal and not common in rock samples found on Earth. However, it is common in meteorites. In 50 different sites around the world, scientists found iridium in this layer of clay.
Where could this have happened?
Some geologists have suggested the Chicxulub crater, a site along the north-east coast of Mexico’s Yucatán Peninsula as the impact zone. Some scientists believe that at the same time, another meteorite hit the earth in the Indian Ocean.
What would be the effects of this?
Some scientists have suggested that such an impact may have put the Earth into a ‘nuclear winter’. The ash and dust could have been so thick as to block out the sun’s rays, causing the temperature on the planet to plummet. Without light, plants could not make their own food. Herbivorous (plant-eating) dinosaurs and then carnivorous (meat-eating) ones would have been affected. The impact may have also produced giant tsunamis (tidal waves) and forest fires across the globe.
Artist’s impression of a prehistoric asteroid impact. Artist: J.T. Bauer, © Queensland Museum.