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Permian

The Permian 290 - 250 million years

In Permian times Britain languished 20 or 30° north of the equator, about where the present day Sahara desert is found.  We were smack in the middle of a newly formed supercontinent, a massive meeting of continental plates, which has been given the name Pangaea (pan-jee-ah).  As you can imagine being this close to the equator it would have been hot, dry and very unwelcoming to life.  Unlike many of the rocks of Shropshire the Permian rocks we find were made on land and are typical of a sandy desert.

At the end of the Permian era, something happened that would affect around 96% of all plant and animal species living on earth.  The world experienced a mass extinction event, something that was so catastrophic that it wiped 96% of all plants and animals off the face of the planet forever. In northern Shropshire we have an exposure of this point in time: a dramatic unconformity between the Permian and the overlying Triassic, at Great Bolas.

Scientists have wondered about the causes of these devastating episodes for many years, trying to explain why so many different types of creatures and plants from so many different environments just suddenly died out.  Whatever the cause, it has to be something that affects the whole planet.

Mount St HelensVolcanoes can have a pretty devastating effect on the planet.  They can punch plumes of ash and gas high into the atmosphere where it can encircle the planet with chilling efficiency.  It’s not the dust that’s the killer with eruptions it’s the gases.  When volcanoes erupt gas trapped in the lava escapes and this is usually nasty stuff, lots of sulphur gases, water and carbon dioxide.  The sulphur reacts high up the atmosphere and makes sulphuric acid droplets, which reflect sunlight away from the planet a long time after the dust has settled.  Carbon dioxide has the opposite effect.  It is called a “greenhouse gas” as it prevents heat from escaping through the atmosphere and radiating into space.  It acts like a thermal blanket, raising the temperature on the surface of the earth dramatically.

This high up reflective layer of sulphuric acid and weak carbonic acid acts to either cool the planet, as the amount of sunlight getting through is much lower than normal, or heat up the earth’s surface, either way causing devastating worldwide climate change.  After a few years all these acids would be washed out of the atmosphere to fall as rain, but acid rain of course.

But volcanoes are erupting all the time, right?  Things aren’t just dropping dead all over the place every time a volcano blows its top, so this has got to be a really, really big volcano loaded with sulphur, or something else.

The trendy mass extinction idea at the moment is the giant comet or asteroid colliding with the earth.  Now this was probably true for the extinction that killed off the dinosaurs, but there is a crater linked to that time.  Is there a crater linked to the Permian mass extinction? We haven’t found one yet, but there are people looking.

Craters are a hard thing to find especially if the asteroid was rude enough to land in the ocean.  Sediments would quickly fill the hole in and ocean crust is being destroyed all the time in subduction zones, in fact there is no ocean crust left older than Triassic so if there had been a Permian ocean impact the evidence has been removed by plate tectonics.

What other possible causes for mass extinctions are there?

The formation of this new supercontinent might have had something to do with it.  With all the smaller continents colliding together, there was a massive reduction in the amount of shoreline and shallow seas available for creatures to live on.  It might also have changed sea currents and wind patterns causing dramatic climate change, disrupting food chains and leading to a mass extinction. 

Any of these climate-changing events might also have unleashed one of the most effective greenhouse gases available – methane.

Methane is even better at preventing heat radiation than carbon dioxide, and it is made by rotting vegetation and animal digestion.  This methane forms crystals in cold sea sediments, and needs to stay cold.  If the sea warms up, massive amounts of methane bubble out of the sea as the crystals melt and this could create a very serious greenhouse effect

It might have been any one of these possibilities, or all of them happening together that led to the death of so many different creatures and removed the marvellous Trilobite from our seas forever.  However the end Permian mass extinction happened only a small percentage of the creatures that experienced would survive.

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