May 19, 2015

What the Deccan did for the Dinosaurs?

The possibility that the extinction of the dinosaurs 66 million years ago may have been caused by the eruption of the Deccan lavas in India has been increased by new research, published in the Geological Society of America Bulletin (doi:10.1130/B31167.1).

A view of the Mahabaleshwar escarpment in the western Ghats, India. Just a small part of the 3.6 km thick pile of lavas that flooded over the Deccan region of India some 66 million years ago? (photo copyright Dr Sally Gibson, Dept. Earth Sciences, University of Cambridge)

Category: May 2015
Posted by: Sarah

Dr Sally Gibson of the Department of Earth Sciences in the University of Cambridge is part of an international research team who have been trying to resolve the ’66 million year’ question. That was when an asteroid hit the ocean off Mexico, coinciding with one of Earth’s biggest mass extinctions – the one that killed off most of the dinosaurs and some 65% of the life of the time. The impact event also coincided with the eruption of lavas over the vast Deccan region of India.

Over the last 35 years since the ‘killer asteroid’ theory was first proposed, scientists have been questioning how exactly the impact killed off so much life and whether the Deccan eruption may have played a role in the extinction, especially as such large eruptions of lavas have been implicated in other mass extinctions, whilst asteroid impacts have not.

Sally Gibson and the team have found that the vast bulk of the Deccan lavas were erupted just 100,000 years after the impact event. They claim that the seismic energy generated by the impact in Mexico was great enough to reverberate around Earth, shaking up the huge magma chambers, which had built up below India, and causing them to spew out over some 500,000 sq. km of the subcontinent’s landsurface. The total thickness of lava has been measured at some 3.6 km with a volume of some 1.3 million cubic kilometres. The eruption produced the most extensive lavas known with flows extending over 1000 km across the entire Indian subcontinent and volumes approaching 10,000 cubic km. Inevitably, the eruption of such large volumes of lava would have released huge amounts of climate-changing gases, such as carbon dioxide, into the atmosphere.

The impact event also caused prolonged atmospheric disturbance and the combined effects may well have driven climate change severe enough to cause the extinction of so many lifeforms.

To appreciate the severity of the 66 million year old extinction – it was not just the dinosaurs that disappeared, visit the Sedgwick Museum and compare the fossil displays from Cretaceous times (before the extinction) with those of Tertiary times, which followed the extinction.

Image: Just a small part of one lava flow from the Mahabaleshwar escarpment in the western Ghats, India. (photo with permission, copyright Mark A. Richards, Dept. Earth and Planetary Sciences, University of California, Berkeley, California, USA)