Saturday, 26 November 2011

What Was The Permian Mass Extinction And What Caused It?

What Was the Permian Mass Extinction?

Have you ever heard of the Permian Mass Extinction, also known as the ‘Great Dying’?  If you are worried by the prophecies that the world as we know it is going to end in 2012, you may not be too cheered by the fact that our planet has already undergone several mass extinctions where a significant percentage of all the animal and plant species then alive were suddenly wiped off the face of the Earth. The mass extinction that we are all perhaps the most familiar with is that of the dinosaurs 65 million years ago, when 70% of all the species on the Earth died out. However, the Permian Mass Extinction was even more devastating to our planet, and yet many people have never heard of this sudden period of mass destruction. The Permian Mass Extinction occurred around 251.4 million years ago and constitutes the borderline between the Permian and Triassic periods.  During the Permian, there was only one big land mass, known as the super-continent Pangaea and the destruction of species was savage, with 70% of terrestrial vertebrates disappearing, 96% of all marine species disappearing, and what is thought to be the only mass extinction of insect species  in the planet’s long history occurring.   The destruction of species was so complete that it took the Earth from 4-6 million years to recover, and when it did the foundations had been laid for the dawn of the age of the dinosaurs. So what could possibly have caused this disaster and wreaked such a trail of total destruction?  The Permian Mass Extinction has baffled scientists, and there have been many theories put forward as to what natural event or chain of events could possibly have caused this maelstrom.

What Are The Possible Causes of the Permian Extinction?

So what type of natural disaster could have triggered what is known as the ‘Great Dying’? Globally most complex ecosystems were destroyed, and with only 5% of all species surviving there was a huge question mark as to whether life on Earth could continue to survive at all. It is believed that the extinction event that led to the end of the dinosaurs was a huge impact event; with the impact of a huge asteroid or comet hitting the earth and triggering global destruction. So could an impact event have been the cause of the Permian Mass Extinction? Many scientists have combed the surface of the Earth for evidence of an impact crater that was large enough to have been the catalyst. One of the problems that they have encountered is the huge 250 million time gap between then and now. There is every chance that the impact crater simply no longer exists. Around 70% of the world’s surface is covered by the oceans, and no part of the ocean floor is older than 200 million years old. This is because the sea floor is destroyed by spreading and subduction, and it has been surmised that extensive lava flow could also have concealed any large crater site.

Basalt Lava Flow

Could A Meteorite Impact Have Caused The Permian Mass Extinction?

So evidence of an impact event at the Permian-Triassic boundary is sparse. In 2001 a team from the University of Washington, led by Luanne Becker, published a paper that outlined their discoveries of extraterrestrial argon and helium in rocks of the right age in Japan and China. These two gases were found trapped in something called fullerenes or buckyballs, which are often linked to debris from meteor impacts. The team’s findings were brought into question by other scientists, but they have stood by their findings. There are also a couple of possible sites that have been proposed as the point of impact 250 million years ago. One of these is the Bedout High off the coast of northwest Australia, which is a 30km in diameter circular area where older rocks have been uplifted by as much as 4 km towards the surface. It has been theorised that the Bedout High may be the centre of a huge buried impact crater that dates towards the end of the Permian period. Another proposed impact site is in Antarctica and is known as the Wilkes Land crater, which is actually two hypothetical giant crater impact sites that are hidden deep beneath the Antarctic ice sheets.  Both of these locations have been questioned by the experts, as it has been queried as to whether the geological structures were really caused by meteorite or asteroid hits.

Did Massive Volcanic Eruptions Trigger the ‘Great Dying’

Can you imagine huge volcanic eruptions that carried on for over half-a-million years? Well the close of the Permian period was marked by massive volcanic events. This type of sustained volcanic activity could have accelerated massive global climate changes, covered huge areas with boiling hot volcanic rock and released tremendous amounts of poisonous gases and ash into the atmosphere. What remains of some of these ancient volcanic eruptions are known as the Siberian Traps, where around two million square kilometres of what now is Eastern Russia was covered with basalt lava.  Usually, these are not the type of explosive volcanic eruptions that form the tall cone-shaped volcanoes that most of us are familiar with, but rather huge amounts of basalt lava is pushed out through long fissures in the rocks spreads across large areas. However, there is evidence from the Siberian Traps, in the form of a large amount of pyroclastic deposits in comparison with other basalt floods, that these eruptions were very explosive pumping vast quantities of gases and ash into the atmosphere. However, again scientists have questioned whether these volcanic eruptions, long lasting and as explosive as they were, would have been enough to cause the extinction on the scale of the ‘Great Dying’.

However, there is new evidence that these massive volcanic eruptions could have been the cause of the Permian Mass Extinction after all.  Scientists from the University of Calgary have discovered layers of coal ash in the rocks dating to the Permian-Triassic boundary in the Canadian Arctic, which they believe were deposited as the result of massive coal combustion that was set off by the volcanic activity. This widespread coal fire would have been responsible for the emission of large quantities of greenhouse gases, at a time when the Earth was suffering from a decrease in oxygen levels, acid rainfall and the effects of massive amounts of toxic ash in the air.

So although it may never be conclusively proved that massive volcanic eruptions are what were responsible for the Permian Mass extinctions, there is a growing body of evidence that suggests that this is the case.  However an impact event as the trigger cannot be totally discounted and it may well be that the meteorite or asteroid comet impact was what started off the catastrophic volcanic activity.  No doubt the Earth will continue to yield new evidence as to what was the cause of this greatest of mass extinctions, and that one day the full story will be known.

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