Volcanic-Eruption Theory

Until the 1980s, most scientists believed that noncatastrophic geological processes caused the extinction of dinosaurs that occurred approximately 66 million years ago, at the end of the Cretaceous period. Geologists argued that a dramatic drop in sea level coincided with the extinction of the dinosaurs and could have extinction as well as the extinction of many ocean species.

This view was seriously challenged in the 1980s by the discovery of large amounts of iridium in a layer of clay deposited at the end of the Cretaceous period. Because iridium is extremely rare in rocks on the Earth’s surface but common in meteorites, researchers theorized that it was the Earth’s climate and thus triggered the extinction of the dinosaurs.

Currently available evidence, however, offers more support for a new theory, the volcanic-eruption theory. A vast eruption of lava in India coincided with the extinctions that occurred at the end of the Cretaceous period, and the release of carbon dioxide from this episode of volcanism could have caused the climatic change responsible of molten rock, called “diapirs,” that can, under certain circumstances, erupt violently through the Earth’s crust.

Moreover, the volcanic-eruption theory, like the impact theory, accounts for the presence of iridium in sedimentary deposits; it also explains matters that the meteorite-impact theory does not. Although iridium is extremely rare on the Earth’s surface, the lower regions of the Earth’s mantle have roughly the same composition as meteorites and contain from the explosive volcanism that occurred as material from the diapirs erupted onto the Earth’s surface.