Friday, February 1, 2013

New evidence for the causes of slow recovery at the P-T extinction event

The Permian-Triassic extinction (also known as the P-T boundary event), occurring 252.28 Ma has been described as the worst mass extinction of all time. Informally known amongst geoscientists as the “Great Dying” it is estimated that 96% of marine species and 70% of terrestrial species became extinct over a period of three “pulses”.
Many reasons have been put forward for the cause of the extinction, and a commonly accepted theory is that the first two pulses were caused by a gradual environmental change and the last was caused by a catastrophic event. Reasons for the catastrophic event have included bolides, extreme volcanism (from the Siberian traps) and marine methane clathrate release leading to cataclysmic changes in the oceans, and there is ample evidence for widespread ocean anoxia during the P-T event.

Biotic recovery was slow, with some palaeontologists estimating that ecosystems took up to 30 million years to recover, and new research undertaken by Ohio State University doctoral student Alexa Sedlacek has suggested that the first stage of recovery (which took around 5 million years) may have been this slow as due to global warming. There is plenty of evidence in the rock record for there being little life (except for disaster taxa- that is, species that are opportunistic and will quickly colonise after ecosystem-collapse events) after the P-T and Alex has been quoted as saying “ It's as if life had a 5-million-year hangover”, and Alexa thinks she’s figured out why.

During the early Triassic there were a series of “giant volcanic eruptions” , known as The Siberian traps (these volcanic eruptions are also believed to be a cause of the extinction as there is evidence they were erupting during the late Permian) and they are estimated to have released up to 4million cubic km of lava, and the gases associated with this would have dramatically altered the atmosphere chemically. Analyses from the rocks gathered in Alexa’s research ( all of the samples came from a limestone in Iran, which was once a tropical sea) show that for the 5 million years after the P-T event, both the atmosphere and the carbon-cycle were unstable, and it wasn't just the Co2 levels they analysed. Also analysed as part of this research were the strontium ratios. Analysis indicates that there was a change in the strontium ratios in the early Triassic oceans from 0.7070 to 0.7082. And, whilst this doesn't seem like a significant change, it actually goes a long way to explain why so much of the marine life died out, and took such a long time to recover. Even this small change was enough to make the oceans hostile and unlivable.

These types of strontium ratio changes would have turned the oceans into a warm (some estimates have suggested temperatures of up to 42C- Although itemperature changes are attributed to other causes), acidic, gloopy (The gloopiness would have come from the changes in strontium ratios. An increase in this ratio indicates increased chemical weathering on the surface of the Earth, and this sediment has to end up somewhere!) mess. As warm as a modern hot-tub and filled with sediment- it’s no wonder that 96% of marine life became extinct, and took so long to recover! For example “Fish would have had silt in their gills, coral reefs would have been buried” and as far as the evidence shows, the only things that really thrived under these conditions were microbes.

So why is this important? Well studying the past can be a good way to predict what is going to happen in the future. Whilst we can all accept that changes in the climate of our Earth are natural- I mean, the evidence taken from causes of the P-T evidence proves that there are natural, and extreme, climate variations- it is impossible to deny that anthropogenic emissions are forcing our climate in ways that they are not meant to. Our oceans are getting warmer (predictions see them as reaching 27C before long, and whilst not as severe as 42C, it is still much warmer than they have been in present times), they are becoming more acidic and our marine life is already facing huge problems, with extinctions occurring at alarming rates. The message from this research is clear. We can’t wait until tomorrow to do something about anthropogenically induced climate forcing, as the roads to recovery are long, and we might just wipe ourselves out too.

For more information head to the links provided below.

Image; P-T boundary at Sambullak, thanks to the University of Bristol.

No comments:

There was an error in this gadget