We’re all going to die! Slowly at first.

Published 2007-10-16 by Chris

This post is part of The Accretionary Wedge blog carnival, issue 2.

You’ve seen Deep Impact and Armageddon. You know there’s asteroids bigger than Texas drifting through space, and when that drift intersects the Earth, it’ll make every horrible hangover you’ve ever had look like the parties that caused them. But the real killers aren’t necessarily going to drop in, but break out. How exactly is the earth going to kill you, well….

Every school-aged child has a set idea on what happened in the final moments of the Cretaceous. A mother and baby dinosaur frolick gaily by the lakeside, volcanoes going about their regular eruptive business in the backdrop. A huge fiery meteor, kilometres-wide, destructively roars through the sky. Mother and baby brontosaurus (though there was never such a species, and Apatosaurus lived in the Jurassic), helplessly stand by as the earth beneath them peals away, consuming everything in sight. The impact’s ejective material shoots into the stratosphere, blocking out the sun for years, and bringing the age of the dinosaurs to an end. Then mammals evolved.

When it comes to the KT (Cretaceous-Tertiary) boundary, however, there was a lot going on. The biological landscape was changing [1] long before the iridium anomaly [2][3] and even impact-generated diamonds [4] appear in the geological record. The extinction may have been capped-off with a dramatic impact, or series of impacts, but the extinction was most likely initiated by the volcanic backdrop [5].

60 – 65.5 million years ago, the Deccan Traps, in western India, were forming. A large igneous province (LIP) erupting material on the scale of 1 million cubic kilometres is nothing to discount. That’s erupting a volume of material the size of California, 2.5 km (~1.5 miles) thick. I’ll save the discussion of how the Deccan LIP formed for another post, but all the nasty sulphuric gaseous, climate changing material you’d expect to come from your run-of-the-mill eruptive event were being expelled in spades through and onto what was at the time, the Indian island continent. Climate change was occurring on a massive scale. Biota variation in the oceans had dramatically fallen [5], with the number of ammonite species dropping from 40 to less than ten in the 3 MYr prior to anything significant falling from the sky (specifically the impactor that generated the Chicxulub crater).

So, enormous eruptions and possible multiple large impact events [6], sounds like a bad million years at work and there’s no reason it couldn’t happen again. We may be looking towards the sky for potential impactors [7], but why not look to the earth? Plotting like a convicted mass murderer, days away from release, the Earth could kill us all and we may not even notice at first (what’s a small, non-explosive eruption here and there?). The climate changing gas release from a LIP eruption like the Deccan Traps, or even worse the Siberian Traps – which coincides with the Permian-Triassic extinction where life on earth was almost completely destroyed – would put our efforts to warm the globe to shame.

References

1. British Broadcasting Corporation, Dinosaur impact theory challenged.
2. Benjamin C. Schuraytz, David J. Lindstrom, Luis E. Marín, René R. Martinez, David W. Mittlefehldt, Virgil L. Sharpton and Susan J. Wentworth,
   Iridium Metal in Chicxulub Impact Melt: Forensic Chemistry on the K-T Smoking Gun, Science 15 March 1996: Vol. 271. no. 5255, pp. 1573 – 1576
3. David H. Elliot, Rosemary A. Askin, Frank T. Kyte, and William J. Zinsmeister, Iridium and dinocysts at the Cretaceous-Tertiary boundary on Seymour Island, Antarctica; implications for the K-T event, Geology; August 1994; v. 22; no. 8; p. 675-678
4. R. M. Hough, I. Gilmour, C. T. Pillinger, F. Langenhorst, and A. Montanari
   Diamonds from the iridium-rich K-T boundary layer at Arroyo el Mimbral, Tamaulipas, Mexico, Geology; November 1997; v. 25; no. 11; p. 1019-1022
5. British Broadcasting Corporation, What Really Killed the Dinosaurs?
6. Leslie Mullen, Multiple Impacts?, Astrobiology Magazine, Oct 20, 2004
7. NASA Asteroid and comet impact hazards

Extinction splash image taken from Blog with a View (Blog with a View (http://cruelanimal.blogspot.com/)

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