What killed the dinosaurs?

November 15, 2009 • 3:07 am

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.

A three-dimensional reconstruction of the submerged Shiva crater (~500 km diameter). The overlying 4.3-mile-thick strata and water column were removed to show the morphology of the crater. Credit: Sankar Chatterjee, Texas Tech University

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.

12 thoughts on “What killed the dinosaurs?

  1. Nice fuzzifying projection – I get that feature as ~20 by 6 sq across, which on the scale is 700×200 km, or by correcting to the claims, 500×150 km. At a 3:1 feature ratio, that would be one glancing impactor at a guess. Color me pink, purple and skeptical. 🙂

    Well, it’s still possible I guess. But the simple hypothesis of the Chixculub impactor now has a _much_ more complex competitor, with at least three coincidental events instead of the simple impactor process spawning off different scales of extinctions.

    Also a problem is that this then is proposed as a hypothesis (on extinction) to support observations (of an impactor), which I don’t think affected the native Chixculub observation.

    Moreover, there are more predictions from this than the simple model. For example, a much higher impact ratio, and a much heightened importance for impactors contribution to extinction events. None of which seems to be observed.

    As this impact observation née extinction hypothesis hasn’t passed peer review, I can afford to take the opposite position to WEIT, this isn’t anything I need to consider. It’s a non-issue for all I care. [Disclaimer: I’m not a geologist or biologist, so I have no stake in this.] But if it make peer review, more’s the power to it.

  2. I will probably get flak for this but does it matter WHICH extraterrestrial impact caused the catastrophic climate changes that led to the extinction of the dinosaurs 65 MYA?

    They are still dead last time I looked.

  3. “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.”

    What does this mean?

    1. Basically that rocks from the time are rich in meteorite material that was melted and launched out of the crater in the direction the meteor was traveling. Basically, imagine that part of the meteorite and the rock it hit was melted on impact, and the liquified material was then launched out of the crater in a wave similar to what you would get if you throw a rock into water at a low (close to horizontal) angle. The wave would spread out from the point of impact, but be much larger in the direction the rock was travelling.

      Iridium is rare in Earth’s crust but common in asteroids, so large amounts of it in a certain layer of rocks is indicative of an impact event (or a volcanic eruption containing material from at or near Earth’s core, which is also rich in iridium).

  4. I’m no geologist – I’ve never even tried to commit the geologic periods to memory – but if the Indian plate collided with Asia 70 MYA (per Wikipedia’s Himilayas page) and India itself was still a huge island (subcontinent?) in the Indian Ocean 55 MYA, can anything on the floor of the Indian Ocean be a credible relic of something that happened 65 MYA?

    (Also per Wikipedia, at the present rate, India should travel 1500km into Asia in the next 10MY!)

  5. Remember Shumaker-Levy? It split into a number of fragments before impacting Jupiter at multiple locations. It is certainly conceivable that the earth received a one-two punch sequence from a fragmented comet or asteroid.

  6. How deep is the feature at this point in time? It’s hard to believe a large meteorite impact on the bottom of the ocean, but if you look around (for example, north of the Marianas Islands) you see numerous (partial) rims of enormous volcanic calderas which form curious strings of islands along an arc. I have no idea of magmatic composition and source depth so I can’t guess if volcanic ejecta may have enhanced traces of iridium.

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