Seth Burgess, U.S. Geological Survey volcanologist, found the smoking gun that caused earth’s greatest mass extinction 252 million years ago at the end of the Permian period. Massive blowholes, called diatremes, blasted extraordinary amounts of the greenhouse gases carbon dioxide (CO2) and methane (CH4) , after earth’s largest preserved volcanic eruption began injecting massive layers of magma into carbon rich sediments. The sudden outburst of carbon dioxide caused rapid global warming and turned the oceans acidic, eliminating over 95% of earth’s marine species and 70% of terrestrial vertebrate species.
Extremely precise determination, by uranium decay series geochronology, of the age of formation of zircon crystals in magma, solved the question of why the Permian extinction happened well after the Siberian traps eruptions began. The massive surface basalt flows did not cause the extinction event. The surface flows did not heat the sediments they covered enough to cause carbonaceous materials to break down into the greenhouse gases carbon dioxide and methane. When the volcanism changed from surface eruptions to intrusive injections of extremely hot basaltic magma, all hell broke loose. The precise time that the magma injections began is the precise time that atmospheric CO2 and temperatures shot up. The normal slow processes of rock weathering, erosion and marine organism growth that maintain stable ocean chemistry were overwhelmed by the rapid injection of acidic CO2, and the oceans became acidic. Then the mass dying began.
Humans are now turning stored carbon into CO2 at a rate that is only rivaled by the end-Permian. Much of the warming potential of CO2 emissions has been hidden by the uptake of heat by cold water layers below the surface of the ocean. Coral reefs are the ocean’s canary. The recent massive bleaching and die off events are the indicators of the developing disaster in the ocean caused by increasing temperature, stagnation and acidity.
Dr. Burgess clearly explained how he found the smoking gun in his original report.
www.nature.com/...
A striking temporal coincidence is instead observed between the extinction event and the emplacement of Siberian Traps sills, which intruded the thick Tunguska basin, composed of evaporite, clastic, carbonate, and hydrocarbon-bearing rocks12. Heating of sediments over the large area encompassed by the sill complex (>1.5 × 106 km2) likely liberated massive volumes of greenhouse gasses12, 25. However, sills were intruded over an interval of ~500 kyr4, while the extinction interval and carbon isotope anomaly are both an order of magnitude shorter. This disparity necessitates that a currently unidentified subinterval of intrusive magmatism during stage 2 is the extinction-triggering aliquant. The oldest sills dated in the magmatic province mark the onset of stage 24, and are the only sills whose emplacement timing is coincident with both the carbon isotope excursion and the onset of mass extinction; all other dated sills postdate these events (Fig. 2), and are thus disqualified as the trigger. Therefore, we suggest that only intrusions emplaced at the beginning of stage 2, during the initial lateral growth of the Siberian Traps sill complex, satisfy all the necessary criteria to qualify as the trigger of the end-Permian mass extinction.
Geologist Howard Lee, writing in the Guardian, interviewed Dr Burgess about the concern that humans are recreating the events that caused the end-Permian extinction: www.theguardian.com/...
Parallels today?
The more science learns of these past greenhouse gas-driven events, the more uncomfortable the parallels to today become. I asked Burgess if it was ridiculous to make the comparison.
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.
A key indicator of what triggered the extinction is found in the carbon. The carbon was “light carbon”, enriched in carbon of mass 12 and depleted in carbon of mass 13. This light carbon outburst is indicative of the natural burning of carbon produced by living organisms. A cataclysmic combination of warming, ocean acidification and rapidly cascading changes caused the end-Permian extinction and may have also triggered a number of less prominent extinction events.
He went on to explain various lines of evidence that point to the source of that carbon being methane and carbon dioxide resulting from magma intruding and cooking organic-rich sediments. He continued:
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.