The cause of the "Great Dying" has been a subject of conjecture for as long as we've known about it. Candidates include:
- The formation of the Siberian Traps, an unimaginably huge lava flow covering most of eastern Siberia. (Its volume is estimated at four hundred million cubic kilometers.) The eruption would have burned everything in its wake, pumping tons of carbon dioxide into the atmosphere, and it would have released huge amounts of sulfur dioxide -- not only a poison, but one of the most powerful greenhouse gases. The result; massive global warming and a catastrophic change in ecosystems worldwide.
- The lockup of Pangaea. The collision of smaller continents to form a supercontinent has a number of effects -- the eradication of coastline along the colliding margin, ecological changes from shifting ocean currents, and collapse of mid-ocean ridges (resulting in a huge drop in sea level) among them.
- A "methane burp." This sounds innocuous, but really, really isn't. There's a tremendous amount of methane locked up in the form of clathrates -- a network of water ice with methane trapped inside. These "frozen methane hydrates" coat the entire deep ocean floor. The stuff is stable under cold temperatures and high pressures, but if something disturbs them, they begin to come apart, releasing bubbles of methane gas. The bubbles expand as they rise, displacing more and more water, and when they hit the surface it causes a tsunami, not to mention releasing tons of methane into the atmosphere, which is not only toxic, it's also a greenhouse gas.
- Bombardment by swarms of comets and/or meteorites. The problem with confirming this hypothesis is that any geological evidence of meteorite collisions would be long since eroded away. If the object(s) that impacted the Earth were metallic meteorites, it's possible that you could use the same technique Luis Alvarez pioneered to explain the Cretaceous Extinction, which wiped out most of the dinosaurs -- enrichment of a layer of sediment by dust that's high in metallic elements not found in large quantities elsewhere. But if it was a comet (mostly ice) or a rocky meteorite, we might not see much in the way of evidence of the event.
Part of the Penglaitan Section [Image by Shuzhong Shen]
Right now, the leading hypothesis is that the eruption of the Siberian Traps is the most likely cause. But that in itself is horrific; it means that this colossal outpouring of lava not only happened suddenly, it happened with no warning. Immediately prior to the extinction event, life was doing just fine -- the biodiversity was high, and there were no minor die-offs to presage the big one that was coming.
"We thought we would see a gradual decline in the diversity of life forms or, for example, certain species that are known to be less resilient than others, we would expect them to die out early on, but we don’t see that, said Jahandar Ramezani, of MIT's Department of Earth, Atmospheric, and Planetary Sciences. "We can say there was extensive volcanic activity before and after the extinction, which could have caused some environmental stress and ecologic instability. But the global ecologic collapse came with a sudden blow, and we cannot see its smoking gun in the sediments that record extinction... The key in this paper is the abruptness of the extinction. Any hypothesis that says the extinction was caused by gradual environmental change during the late Permian — all those slow processes, we can rule out. It looks like a sudden punch comes in, and we’re still trying to figure out what it meant and what exactly caused it."
So that's pretty scary. The idea that something on this scale could strike with essentially no warning whatsoever makes me realize how precarious life is, and how easily the interconnections between ecosystems that keep everything going could be disrupted -- not to mention the scale of the destruction if that happens.
Anyone out there still wondering why I'm so alarmed at the rate at which we're pouring fossil-fuel-derived carbon dioxide into the atmosphere?
Anyhow, that's our cheery message for today. Monkey around with the ecosystem, and you could kill 95% of life on Earth. I mean, I don't think it's likely to happen day after tomorrow, or anything, but the fragility of it all should give you pause.
This week's Skeptophilia book recommendation is a fun one. If you've never read anything by Mary Roach, you don't know what you're missing. She investigates various human phenomena -- eating, space travel, sex, death, and war being a few of the ones she's tackled -- and writes about them with an analytical lens and a fantastically light sense of humor. This week, my recommendation is Spook, in which she looks at the idea of an afterlife, trying to find out if there's anything to it from a scientific perspective. It's an engaging, and at times laugh-out-loud funny, read.
[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]