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How could the Siberian Traps cause global mass destruction?
The immediate area would be affected by such things as lava and pyrocastic flows but how does this affect the other side of the world? The real power of the Siberian Traps was the climate altering potential by the emission of ash and gases. The Siberian Traps is recognised as having a large proportion of pyroclastic deposits relative to other flood basalts. This indicates an explosive nature with much ash and gases being pumped into the atmosphere. All of this ash and gas has two main effects that, even though they are opposite to each other, act on differing timescales.
Initially sulfur aerosols and volcanic ash envelop the earths atmosphere blocking out sunlight and sending surface temperatures plunging . Ash and sulphur aerosols can remain in the upper atmosphere for 100's to 1000's of years which would be enough to cause a significant glaciation. At the end of the Permian period the biggest ever drop in sea level in history occurred. Two scientists named Holser and Magaritz in 1987 proposed that such a marine regression could be caused by a large scale glaciation.
The second major effect is the emission of greenhouse gases such as CO2, methane and also water vapour. Green house gases warm the climate by allowing sunlight to pass through, heat reflected by the Earth itself cannot penetrate the atmosphere so is retained. Greenhouse gases stay in the atmosphere much longer so their climate changing effects can last for millions of years.
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Another minor effect is the destruction of the ozone layer caused by gas emissions. Chlorine and fluorine gases are erupted from almost all volcanic eruptions and these destroy the ozone layer. Without the ozone layer, harmful UV rays can kill organisms therefore contributing to a mass extinction.
Unlike the paleontological record, the [geomagnetic] reversal record is fairly clean, at least for the past 165 million years of geologic time. About 300 complete reversals have been found in this interval, most well dated. There are smoe very long-term trends in the number of reversals per million years, and these have been known and accepted for many years -- even though there are no good explanations for them... I was encouraged to find a recent paper claiming periodicity in the number of reversals through time... J.G. Negi and R.K. Tiwari... concluded that there is a 32-million-year periodicity... a French group, headed by A. Mazaud, claimed a 15-million-year periodicity positioned in time such that every other pulse was a bit stronger and fell approximately at one of our extinctions... On the other hand, the problem had been looked at by a number of other geophysicists over the years... They had been unable to reject a hypothesis of randomness... I found an impressive 30-million-year periodicity that matched the extinction periodicity fairly well... Nature... neither accepted nor rejected the paper but returned it to me (with the reviews) to revise and resubmit. At the same time, I was invited to suggest the names of six additional reviewers. [pp 183-185]Dr. David RaupFor a while, I thought mass extinctions were merely instances of chance coincidence of independent species extinctions. That clearly was wrong... I have come to the view that large-body impact is responsible for far more extinctions that we appreciate -- perhaps including those pulses of extinction that usually define stratigraphic stages. Maybe even zones? ...For periodic extinction, I know of 13 complete re-analyses of the Sepkoski data that have been published by independent investigators. Of these, five found our periodicity to be significant whereas eight found no significant periodicity. Had these studies used the new genus-level data, I suspect periodicity would have fared better. In any event, the periodicity of extinction must, I think, remain an open question until we have either more data or data of a completely different kind... I believe they really are periodic but I cannot prove it. One problem is that in time-series analysis, one can establish a departure from randomness rather easily but proving a particular periodicity within that is nearly impossible... The extinction record has been analyzed about as thoroughly as possible and searches for Nemesis have failed to find the companion star... I think periodicity is on the back burner but not forgotten -- any more than continental drift was forgotten.
interviewed by Steve Brusatte
Dino Land Paleontology
1997