Climate - Extinctions

Since the early 1980s, the 'asteroid theory' proposed by American scientists Walter Alvarez and Luis Alvarez has attracted a great deal of attention. This theory suggests that the extinction may have been triggered by an asteroid hitting the Earth, which ejected a large amount of rock into the atmosphere, leaving the Earth in darkness for several months or longer. The inability of sunlight to pass through this dust cloud on the planet is thought to have caused photosynthesis to stop, killing green plants and disrupting the food chain. There is plenty of evidence in the rock record to support this hypothesis. A giant crater from the Late Cretaceous period, 112 miles in diameter, was found buried under sediments on the Yucatan Peninsula near Chicxulub in Mexico. Extinction-related sediments have also been found to contain tektite and the rare earth element iridium, which is only found deep in the Earth's mantle and in extraterrestrial rocks. In addition, spectacular secondary effects of the impact have been identified, such as the massive tsunami that traveled along the coast of the Gulf of Mexico and the widespread forest fires caused by the impact's fireballs.