Tuesday, December 20, 2005

Permian-Triassic mass extinction

About 252 million years ago, at the end of the Permian geologic period (and the beginning of the Triassic), more than 90% of marine organisms and about 70% of terrestrial vertebrate species went extinct. This Permian-Triassic extinction event is the most extensive instance of mass extinction that is known -- considerably more severe than the Cretaceous-Tertiary extinction event (KT event) of 65.5 million years ago that wiped out the dinosaurs.

There is even more uncertainty about what caused the PT event than there is about the later KT extinction. Hypotheses include:

  • an impact event (similar to the currently favored explanation of the KT event) that could have led to either immediate superheating of the atmosphere causing widespread fires, and/or a subsequent "nuclear winter effect" due to lingering particulates that caused drastic cooling
  • large-scale gasification of methane hydrate in the oceans, producing quantities of methane gas that led to a greenhouse effect and a 5°C average rise in global temperatures
  • volcanic eruptions, probabaly in the Siberian Traps, that would have produced acid rains, greenhouse gasses, temperature fluctuations, and eventually severe depletion of oxygen dissolved in the oceans
  • other possibilities, such as a nearby supernova, or perhaps a combination of several of these possibilities

Recently reported research argues for the explanation involving volcanism:

No safe ground for life to stand on during world's largest mass extinction
[A]nalysis of a unique set of molecules found in rocks taken from the Dolomites in Italy has enabled scientists to build up a picture of what actually happened. The molecules are the remains of polysaccharides, large sugar-based structures common in plants and soil, and they tell the story of the extinction.

The molecules date from the same time as a major volcanic eruption that caused the greatest ever outpouring of basalt lava over vast swathes of land in present day Siberia.

The researchers believe that the volcanic gases from the eruption, which would have depleted earth's protective ozone layer and acidified the land and sea, killed rooted vegetation. This meant that soil was no longer retained and it washed into the surrounding oceans.

The chemistry of the rocks reveals that although the sugar molecules were found in marine sediments, they derived from land, supporting the theory that massive soil erosion caused them to end up in the sea.

Soil materials in the oceans would have blocked out light and soaked up oxygen. Analysis of rock chemistry suggests that after the soil crisis on land, the marine ecosystem succumbed to the stresses of environmental change and oceanic life faltered, completing a global catastrophe.


Another account: Geologists Link the "Great Dying" to Volcanism


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Blogger Giacomo said...

Interesting evidence suggests that mass extinctions may have occurred very differently than previously thought

3/18/2007 03:34:00 PM  
Blogger Charles Daney said...

First off, there are several possible causes for a mass extinction, and different ones may have been involved in different cases.

The research reported in this post suggests vulcanism was responsible for the PT extinction. Other possibilities, such as release of undersea methane, may still be viable.

In the case of the KT event, most signs point to an asteroid impact. However, there is a dispute over whether the Chicxulub Crater on the Yucatan coast is a remnant of that impact, or whether some other perhaps unknown crater is the actual impact site.

3/18/2007 11:35:00 PM  

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