In a diary on top of the recommended list, Fishoutofwater quotes from a new paper on the cause of the permian mass extinction, the largest extinction known from earth's history. The conclusion drawn is that coal combustion, triggered by Siberian volcanic eruptions, caused the mass extinction. The implication of the diary is that our burning of fossil fuels is re-creating the conditions that led to this extinction. With all due respect to the diarist for reading scientific literature, the paper makes the usual mistake of attributing the extinction to only one cause, and not the multiple causes usually present.
Causes proposed for this mass extincton include:
- collision of all the continents into Pangea, and the resultant loss of shallow water habitat,
- eruption of the Siberian Trap basalts, and the resulting release of particulates and sulphur compounds,
- a meteorite impact and the resulting "nuclear winter",
- burning of coal (the new theory), and
- changes in ocean geochemistry as a result of increased carbon dioxide in the atmosphere.
A more likely scenario is that all of them occurred.
- Over the end of the Permian, all the continents on earth collided, to form a single supercontinent called Pangea. Half or more of the shallow continental shelves were gradually wiped out in collisions, and when the rate of plate movement slowed down, and ocean plates cooled and sank, sea level dropped, drying up much of the rest of the continental shelves. Since extinction was greatest in shallow marine environments, this alone would have stressed the critters living there. This factor alone is not the sole cause of the extinction because it was too slow.
- There is evidence for one or more craters in the southern hemisphere. A 300 km crater is suspected to be present beneath the Antarctic ice sheet. Impact debris from a smaller crater in the ocean off of Australia (close to the site of the larger crater) has been found that shows the shocked quartz and impact melt associated with giant impacts. The date of the impact melt is the end of the Permian, when the extinctions occurred. These impacts were larger than the Chixulub impact which wiped out the dinosaurs.
- The Siberian Trap basalts erupted at the end of the permian and afterward. They were located directly opposite the spot on earth of the 300 km. diameter "crater" in Antarctica. Shock waves from a giant impact spread outward around the earth and then concentrate at the antipodal point. Fracturing of the Earth's crust allows partial melting of mantle materials to erupt as basalts. The Deccan Traps in India were antipodal to the Chixulub impact, and occurred at the end of the Cretaceous, when the Chixulub meteorite hit. So the basalts might have contributed to the extinction, but were caused by the meteorite.
- The coal in Siberia may have burned, resulting in the ash found in the extinction horizon, but the ash also might have been caused by the massive forest fires triggered by the impact itself.
- and yes, release of massive amounts of carbon dioxide into the atmosphere from coal and/or the forests would have caused chemical disruption and acidification of the oceans.
The point of this exercise is that there are multiple causes of the Permian extinction, most of them interrelated. Life would have been wiped out by the impact in a substantial portion of the Earth due to the shock waves, the earthquakes and giant tsunamis. Ejecta into the atmosphere would have triggered a "nuclear winter", shutting out sunlight for years. Volcanic eruptions on the other side of the Earth would have devastated large areas for thousands of years. Coal fires from these eruptions would have led to global warming and disruption of oceanic chemistry. Small wonder that most of life on Earth died.
I am not a global warming denier. It is happening, and it is the result of burning of fossil fuels. However, burning coal is NOT recreating the conditions found at the end of the Permian, it is reproducing only one part of those events. It's not even certain we are burning as much coal now as was burned in the Siberian trap basalts.
It's perfectly fine to learn from the past in order to predict the future using science. There are more than enough good scientific reasons to cut our dependence on coal and oil. But we don't need to overstate the case by blaming mass extintions on global warming.