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Volcanoes Killed Off Dinosaurs

Researchers say volcanism more likely caused K-T extinction; not asteroid impact

Addressing the age-old question of what really happened to dinosaurs, researchers at Princeton University say they have found more evidence that it was volcanism, not an asteroid impact that killed them off.

According to the asteroid-impact theory, put forward in 1980 by physicist Luis Walter Alvarez, the Cretaceous-Tertiary extinction, or the K-T mass extinction, which killed off the dinosaurs and caused the extinction of about 70 percent of life on Earth, was caused by a massive impact.

Artist’s rendering of bolide impact. Made by Fredrik. Cloud texture from public domain NASA image.

The asteroid-impact theory is supported by Chicxulub crater in Mexico’s Yucatan Peninsula, which was discovered by geophysicist Glen Penfield, while searching for oil. The 65-million year old crater occurred about the time of the K-T event.

Other theories citing climate change and volcanism have been suggested more recently. Gerta Keller of Princeton University says her studies point the blame toward volcanism.

The Deccan Traps

An intense period of colossal volcanic eruptions, which began about 67 million years ago, earlier than the impact, was regarded as another potential culprit. The eruptions  formed the Deccan Traps in India.

The Deccan Traps formed between 60 and 68 million years ago, at the end of the Cretaceous period. The bulk of the volcanic eruption occurred at the Western Ghats (near Mumbai) some 66 million years ago. This series of eruptions may have lasted fewer than 30,000 years in total. The gases released in the process may have played a role in the Cretaceous–Tertiary extinction event, which included the extinction of the dinosaurs. [Wikipedia]

The Deccan Traps are a large igneous province located on the Deccan Plateau of west-central India (between 17-24N, 73-74E) and one of the largest volcanic features on Earth. They consist of multiple layers of solidified flood basalt that together are more than 2,000 m thick and cover an area of 500,000 km². The term ‘trap’, used in geology for such rock formations, is derived from the Swedish word for stairs (trappa, or sometimes trapp), referring to the step-like hills forming the landscape of the region.

Before the Deccan Traps region was reduced to its current size by erosion and continental drift, it is estimated that the original area covered by the lava flows was as large as 1.5 million km², approximately half the size of modern India. The present volume of directly observable lava flows is estimated to be around 512,000 km³.

The release of volcanic gases during the formation of the traps “contributed to an apparently massive global warming. Some data point to an average rise in temperature of 8 °C (14 °F) in the last half million years before the impact at Chicxulub.” [Wikipedia]

Climate Change

Extreme climate change may have been caused by both the bolide impact and the volcanic explosions; in either case  massive volumes of sulfur dioxide [creating acid rains,] dust and other particles into the atmosphere would have significantly altered the climate.

In fact, some researchers believe a combination of events may have caused the mass extinction, with the asteroid impact finalizing the event.

According to Keller, however, the asteroid-impact “theory is now facing perhaps it’s most serious challenge from the Deccan volcanism and perhaps the Chicxulub impact itself.” She said at a news conference at the annual meeting of the American Geophysical Society in San Francisco.

The Cretaceous–Tertiary extinction event, which occurred approximately 65.5 million years ago (Ma), was a large-scale mass extinction of animal and plant species in a geologically short period of time. Widely known as the K–T extinction event, it is associated with a geological signature known as the K–T boundary, usually a thin band of sedimentation found in various parts of the world. K is the traditional abbreviation for the Cretaceous Period derived from the German name Kreidezeit, and T is the abbreviation for the Tertiary Period (a historical term for the period of time now covered by the Paleogene and Neogene periods). The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era.[1] “Tertiary” being discouraged as a formal time or rock unit by the International Commission on Stratigraphy, the K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers. [Wikipedia]

Deccan Traps near Pune, state of Maharashtra in western India. This file is licensed under the Creative Commons Attribution 3.0 Unported License. Credit: Kppethe.

Keller and her colleagues have recently analyzed geological records in India, Mexico and Texas to  determine the time of impact and the period of volcanic activities in relation to the K-T event. Their examination of sediment layers suggests that the crater impact occurred about 300,000 years before the K-T boundary, and had little or no effects to biota.

“There is essentially no extinction associated with the impact,” Keller said.

On the other hand, the peak of the Deccan volcanic explosions seems to have occurred “just before the K-T boundary,” according to a University of Paris geophysicist, Vincent Courtillot.

After the first volcanic flow, “the species disappear; we have essentially very few left [their recovery is stalled by the two subsequent flows and] by the fourth flow, the extinction is complete,” Keller said.

Courtillot study compares the amounts of sulfur dioxide emitted to the atmosphere by various events as follows, concluding that the Deccan traps are much more likely to have caused the K-T event than the asteroid impact :

• The 1991 Pinatubo eruption: 0.017 billion tons of sulfur dioxide (SO2)
• The Chicxulub crater:  500 billion tons of SO2
• The Deccan traps: 10,000 billion tons SO2.

“If there had been no impact, we think there would have been a mass extinction anyway,” Courtillot said.

Confirming Courtillot’ team and her own findings, Keller added: “Deccan volcanism is the likely culprit behind the K-T mass extinction.”

Related Links:

• Volcanoes, Not Asteroid, May Have Killed Off Dinosaurs