In the history of our planet it was very often that nothing much happened. Only separated by tens of millions of years there was catastrophe – on a global scale – the scale that leaves dents in the fossil record: mass extinctions.
Mother of mass extinctions
The largest of them all, ´the mother of all mass extinction events´ or The Great Dying, may-or-may-not have been finished off by the impact of something as hard, hurtful and imaginable as a meteorite [all we know is the candidate craters are either too young or in fact no impact crater at all], but it was set in place and started by that one common, invisible, scentless and almost non-toxic gas we exhale: CO2.
Its dramatic increase led to warming, triggering a whole range of responses that killed an estimated 90 percent of marine biodiversity, and that warming killed a staggering 96 percent of marine biodiversity and for instance 70 percent of terrestrial vertebrate species. It is the only event in Earth’s history that qualifies as a true mass extinction among insects.
And what’s more: it even wiped out the forests.*
[*) In fact, the Permain-Triassic mass extinction killed so many terrestrial plants, that the following geologic period started with the so called 'coal gap'. On land there simply wasn't enough photosynthetic capacity left to create the required amounts of biomass.]
Because we like geological detours, let’s first not get to the point, but to Pangaea. Two weeks ago we looked at the Triassic-Jurassic mass extinction, some 200 million years ago, that was caused by a large climatic warming event after the break-up of supercontinent Pangaea led to the release of enormous amounts of first [volcanic] CO2 and then methane [from disturbed clathrates – a positive warming feedback] into the atmosphere.
Today we go 50 million years further back in time, to when Pangaea was still very much fixed together, though far from geologically quiet.
Pyroclastic eruptions and flood basalts
Sometimes when Gaia has another of her grumpy episodes she doesn’t feel like tearing continents apart, but she does appreciate to throw some fire around. It is considered one of the largest known volcanic events on Earth and it happened deep in the midst of the continental plate of Pangaea, in a part that is now Siberia.
Immense flood basalts were accompanied by pyroclastic eruptions and together produced the Siberian Traps, an area of 2 million square kilometers of volcanic rock, which formed suddenly, on the Earth’s surface. With the pyroclastic explosions came enormous amounts of ash, so it is presumed the eruptions may have first led to a drastic cooling.
Burning the Earth’s coal, attempt 1
The following lava streams entered carbonate rocks and coal beds, from which they in turn released enormous amounts of CO2, perhaps equivalent to 3 trillion tonnes of pure carbon, or some 11 gigatonnes of CO2, a 2010 Nature Geoscience study estimates, quite suddenly switching the world from cooling to heating.
And this time again there may have been added methane from the clathrates feedback too, aggrevating the warming, possibly even directly triggered by the Siberian flood basalts. Just how large this methane rise must have been is not yet fully reconstructed from the carbon isotope record.
All in all we can imagine the Earth’s climate took a pounding, with temperatures rising multiple degrees*, precipitation patterns changing over an already large [thus dry] continent, acidification and anoxia increasing in the oceans – and that this must have had large effects on the terrestrial biosphere too.
[*) It is thought the P-T boundary is accompanied by a temperature rise of 6 degrees around the equator, and more towards the poles.]
Plagues: the climate-biodiversity feedback
Today we witness a multi-year plague of pine beetles in the boreal forests of Alberta and British Columbia. The insects are native to the forests, the fact that they no longer freeze to their deaths at -35 degrees Celsius – because winters don’t get that cold anymore – is not.
It is just one example of a climate plague, that acts as a feedback on the carbon cycle, releasing megatonnes of CO2, and on biodiversity loss.
We also know such positive climate feedbacks in forests are not confined to insect plagues only. Such feedbacks can operate through microorganims too.
And that is indeed what happened at the end of the Permian, say researchers of Utrecht University, Imperial College London and University of California-Berkeley, in their publication of Saturday’s edition of Geology.
A tree may be able to withstand 6 degrees warming, it may not be able to survive all the bonuses that come along with it, like forest fires – or fungi.
“Throughout the world, latest Permian records of organic-walled microfossils are characterized by the common presence of remains of filamentous organisms, usually referred to the palynomorph genus Reduviasporonites.”
“By analogy with present-day forest decline, these findings suggest that fungal virulence may have been a significant contributing factor to widespread devastation of arboreal vegetation at the close of the Permian Period.”
Or in simple English: what killed the conifer forests of 250 million years ago, could also strike the pine forests of present day Siberia. And these taiga forests themselves store already hundreds of gigatonnes of pure carbon – not the scale of the Permian-Triassic carbon release, but potentially a very nasty extra. With positive feedbacks everything is speculation until you truly pass the tipping point.
© Rolf Schuttenhelm | www.bitsofscience.org