Underground magma triggered Earth’s worst mass extinction with greenhouse gases | Howard Lee

There are parallels between today’s and past greenhouse gas-driven climate changesCoincidence doesn’t prove causality, as they say, but when the same two things happen together over and over again through the vast span of geological time, there must be a causal link. Of some 18 major and minor mass extinctions since the dawn of complex life, most happened at the same time as a rare, epic volcanic phenomenon called a Large Igneous Province (LIP). Many of those extinctions were also accompanied by abrupt climate warming, expansion of ocean dead zones and acidification, like today.Earth’s most severe mass extinction, the “Great Dying,” began 251.94 million years ago at the end of the Permian period, with the loss of more than 90% of marine species. Precise rock dates published in 2014 and 2015 proved that the extinction coincided with the Siberian Traps LIP, an epic outpouring of lava and intrusions of underground magma covering an area of northern Asia the size of Europe.It’s clearly not the entirety of the LIP that’s guilty. There’s a subinterval that’s doing the work, and I set out to figure out which subinterval that was, and what makes it special.In Siberia you have got the Tunguska Basin which is a thick package of sediments that contain carbon-bearing rocks like limestone and coal. When you start intruding magma, [it] cooks those sediments and liberates the volatiles. So the deadly interval of magma in the entire Large Igneous Province is the first material to intrude and pond into the shallow crustThe diatremes that have been mapped are the geologic representation of that gas escape on a catastrophic level. Our hypothesis is that the first sills to be intruded are the ones that really do the killing [by] large scale gas escape likely via these diatremes.The Burgess et al paper is a crucial step towards a new understanding of the role of volcanism in driving extinctions. It’s not the spectacular volcanic eruptions that we should pay attention too - it’s their quiet relative, the sub-volcanic network of intrusions, that did the job. The new study shows convincingly that we are on the right track.There are 3 primary lines of evidence that support that link. The first is: right before the onset of the mass extinction we have evidence for a massive input of isotopically light carbon into the marine system.Just prior to extinction and persisting after the mass extinction the sea surface temperature is thought to have gone up about 10°C. You get that increase by pumping greenhouse gas into the atmosphere. So that’s the second.And then the third line of evidence is a physiologic selectivity to the marine mass extinction. Organisms that make their shells out of calcium carbonate suffer much higher mortality than organisms that make their shells out of silica, for example, which suggests that the ocean was acidified, and you get that by pumping gases like CO2 into the atmosphere.There is a cacophony of kill mechanisms, and I think that this first pulse of sills is the trigger for quite a few of those, sitting at the top, and beneath it are a cascade of negative effects from ocean acidification to climate warming and on down the line.Only Large Igneous Provinces characterized by sills intruded into a volatile-fertile basin are going to be lethal on a global scale.The Deccan Traps doesn’t satisfy those 2 criteria. It’s predominantly flood basalt lavas erupted onto old granitic rock. Acting alone there would likely have been negative effects on the biosphere because of the gases and the particulate matter released by those lavas, which are not insignificant, but I would argue that acting alone it would have been minor relative to the observed mass extinction. But with the Chicxulub impactor sharing the causal burden together they caused the mass extinction at the end of the Cretaceous.No, I don’t think the comparison is ridiculous at all, and I think that the timescales over which the environment changes associated with mass extinctions are frighteningly similar to the timescales over which our current climate is changing. The cause might be different but the hallmarks are similar.The Anthropocene will more likely resemble the end-Permian and end-Cretaceous disasters, rather than the PETM. Continue reading...