Saturday, 26 November 2011

Permian-Triassic mass extinction

what we know? 

This was a massive extinction event, the biggest in geological history, which occurred around 251million years ago, marking the end of the Palaezoic year. This event itself was not abrupt, there being a gradual decline in species over several millions of years.

  • Around 95% of all marine invertebrates became extinct  e.g trilobites,tabulate corals , rugose corals and many braciopods 

Hypotheses to explain the Permian-Triassic mass extinction 

Supercontinent formation - at the end of the Permian, Pangaea was formed when all the world continents collided together. The evidence to support this landmass comes from plate reconstructions and the stratigraphic record. This presence of one large landmass had several effects: 
  • There where fewer continental shelves - lack of habitat for shallow marine dwellers, which is backed up by the evidence of 95% of marine life becoming extinct. 
  • Presence of single continent caused rapid flunctions in climate, and unstable weather patterns 
  • A single continent reduced the imput into the oceans from rivers and estuaries. this would have significantly decreased the amount of nutrients  available for shallow marine life and may have altered the salinity of the oceans.
  • Widespread glaciations occured in the southern hemisphere . caused sea level fall (regression) 

Major volcanic activity (Siberian traps) - this is believed to be the largest volcanic eruption in Earth history. It is probably not a coincidence that  they correspond with the largest extinction event in geological history. The volcanic rocks are largely flood basalt's, thought to be form a large mantle plume intersecting the surface. Today the volcanic rocks cover an area the size of Europe about two million km^2 . The eruptions were thought to last for around one million years. The volcanic activity had several effects:

  • Emission of poisonous gasses would kill many animals and plants in close proximity.
  • The gases and ash would have initially lowered global temperatures by blocking the heat from the sun. This cooling event would have lasted for hundreds of thousands of years. 
  • The emission of greenhouse gasses such as CO2 ans SO2 could have caused an increase in global temperatures, after the cooling period had ceased. this effect is believed to have lasted for hundreds of millions of years.

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