Dead Dinosaurs and Gases
The most widely accepted hypothesis for the extinction of the dinosaurs is the impact of an asteroid at Chicxulub, Mexico (Alverez and Asaro, 1990). An alternative hypothesis, that voluminous volcanic eruptions blocked the sun and caused extreme environmental conditions, has also been proposed (Officer and others, 1987; Courtillot, 1990). Photo of the dinosaur quarry at Dinosaur National Monument. Photo courtesy of the National Park Service.
The key to the volcanic hypothesis is the Deccan Traps, a flood basalt province in India. About 65 million years ago, coincident with the extinction of dinosaurs, a least one million cubic km of lava was erupted. Scaling upwards from the Laki eruption, the Deccan Traps eruption might have created 8-17x1012 tonnes of sulfur acid aerosol, about 100 times more than Laki.
Released suddenly, such a great volume of gas would produced dire environmental consequences, including mass extinctions. Critical to this hypothesis is the rate at which the lava was erupted and the gas released. Some evidence suggests the eruptions happened over a long period, perhaps allowing the atmosphere to recover between eruptions. Features within continental flood basalt lava flows (Self and others, 1997) and the presence of soil horizons at the Deccan Traps argue for a gradual emplacement of the lava flows. This could mean the impact of individual eruptions were no greater than that of Laki.
If the flux rate of iridium at Hawaiian volcanoes is representative of continental basaltic systems, the production rate of iridium by volcanoes cannot account for all of the iridium observed at the K/T boundary (Finnegan and others, 1990). This suggests another source of iridium was involved, possibly from an extraterrestrial source.
An even larger eruption of flood basalts (1.5 million cubic km) at the Siberian Traps at the end of the Permian is linked with the greatest mass extinction Earth's history.