Tuesday, 10 January 2012

All in a lava

The extinction event at the end of the Permian is known as The Great Dying. Sounds sad, doesn't it? It is - lots of things died. If the saying about tragedy plus distance making comedy is true, it ought to be really funny, given it happened around 252 million years ago. It's not, though. In the sea, 96% of species went down the plughole, while 70% of land-based vertebrate creatures became even more land-based. In the space of about 200,000 years an estimated 83% of all the planet's genera were gone.

As with many such situations, working out exactly what happened is a long, on-going process but there is plenty evidence to suggest that a main cause may have been an enormous bout of volcanic activity. The Siberian Traps are a massive span of flood basalts, which were spewed out over a long period of time and covered up to 2 million square kilometers, or more, depending on your sources. This happened immediately before and during the extinction event, and threw inordinate amounts of nasty stuff up into the air with predictably dire consequences. The reflection of solar light and heat, the greenhouse effect of the gases in the atmosphere on the ozone layer, huge CO2 levels causing climate change, acid rain caused by the sulphur and, well, everything just being so dirty. All of these things are essentially bad for anything just trying to get by. Disruption of photosynthesis leads to a domino effect on the food chain, and adverse environmental conditions for a protracted period led to extinction on a scale not seen before or since.

Whether the Traps on their own were enough to cause all the destruction is a matter for debate. Although the K-T event that snuffed out the dinosaurs is heavily associated with a meteorite impact, there was more going on at the time. The Deccan Traps in India, another huge volcanic series, are considered an important factor. Inevitable comparisons prompted the search for a corresponding meteorite for the Great Dying. So far, though, a suitable culprit has not been found and it's not likely signs of a crater would have survived this long in any recognisable state. It's possible, though, that a series of problems was triggered by the formation of the Traps which combined in effect to compound the difficulties life on Earth was facing. Methane released by the Siberian eruptions led to a severe episode of global warming, damaging enough in itself, but also subsequent oceanic anoxia as a dropping temperature differential prevented adequate circulation of oxygen within the waters. Chain reactions...

It's reassuring to place these occasions in the context of geological time. We're not likely to see volcanic activity on the scale of the Siberian or Deccan Traps. If we do, though, it'll be pretty bad news. Even panic buying rice and beans may not be enough to save us.

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