by Matthew Cobb
[Apologies for cross-posting – this appeared last week over at z-letter.com, but I felt it could do with a wider outing!]
In the 1980s, the Alvarez (père et fils) first suggested that an extraterrestrial impact caused the catastrophic climate changes that led to the extinction of the dinosaurs – and loads of other stuff – 65 MY ago. The location of that impact is now widely thought to have been the Chicxulub crater on the Yucutan Peninsula in Mexico. Other suspects for the death of the dinosaurs include the Deccan Traps, a massive area of igneous rock in India that is more than 2 km thick and covers 500,000 km2. These rocks, formed 60-68 MY ago, would have led to massive release of sulphur dioxide, which wouldn’t have made the climate any nicer.
However, over the last few years, Sankar Chatterjay of the Texas Technical University, has been arguing that a submarine structure off the western coast of India, which he has called “Shiva”, is in fact a massive crater produced by a meteor strike. “Shiva” – if it exists – is 500 km across, and would be indicative of a a meteor about 40km wide – nearly 10 times larger than the estimated size of Chixculub object.
Dr Chatterjee recently presented his ideas at a meeting of the Geological Society of America (GSA), in a 15 minute talk. Here’s an extract from his abstract which describes the catastrophic consequences of such an impact:
The impact was so powerful that it led to several geodynamic anomalies: it fragmented, sheared, and deformed the lithosphere mantle across the western Indian margin and contributed to major plate reorganization in the Indian Ocean. It initiated rifting between India and Seychelles in the west and created the Laxmi Ridge; it shattered the Indian plate easterly along the Narmada-Son Rift extending 1500 km across, dividing the Indian shield into a southern peninsular block and a northern foreland block. Because of topographic barrier of the Western Ghat Mountain range, the impact-triggered tsunami was restricted along the Narmada-Son Rift at the KT boundary. The relationships between large meteoritic impact, hotspot, flood basalt volcanism, plate tectonics, geodynamic anomalies, and sudden environmental catastrophe on Earth may open up a new field of unified investigation. Although the Reunion hotspot responsible for Deccan eruption was close to the Shiva crater in time and space, impact probably triggered a component of the Deccan Trap: the iridium-rich alkaline igneous complex rocks that were emplaced asymmetrically as a fluid ejecta at the KT boundary along the NE downrange direction of the bolide trajectory outside the crater ring. Two large impacts such as Shiva and Chicxulub in quick succession on the antipodal position, in concert with Deccan eruptions, would have devastating effects globally leading to climatic and environmental catastrophes that wiped out dinosaurs and many other organisms at the KT boundary.
For the non-geologist, it’s hard to know whether Chatterjee is right or not. In fact, it may be hard for the geologists, too, as this idea has been floating around since at least the 2003 meeting of the GSA, when Chatterjee gave a similar talk. Although he published a paper in Museum of Texas Tech University Special Publications in 2006 (available here), this is clearly an issue that needs to be addressed in a major peer reviewed journal, to help the rest of us decide whether he’s really found evidence of what would be more than a smoking gun – it would be a veritable smoking howitzer.