Filed under: Altithermal, book, climate change, coral reefs, deep time, Hot Earth Dreams, Uncategorized | Tags: asteroid strike, climate change, Wilkes Land gravitational anomaly
Another little post, this one on a news item a few months old. Whenever someone spots a gravity anomaly in Antarctica, people get silly, write things about how the tinfoil hat brigade think it’s a UFO, or an alien base, or NAZIs. They’re so silly. Of course it’s shoggoth (not sure what the singular or plural is. Since shoggoth is sort of like concrete or nanotech, is it singular, plural, collective singular, collective plural, or what?). Anything that close to the Transantarctic Mountains has to be. it’s canon.
More seriously, there’s some potentially interesting science buried under the ice. The idea (per von Frese et al’s “GRACE gravity data target possible mega-impact in north central Wilkes Land, Antarctica“) is that the GRACE satellites found the stated negative gravity anomaly. It’s more than twice the size of Chicxulub, about the size of the 2 billion year-old Vredefort Crater in South Africa, so they’re proposing that it’s the missing crater for the asteroid that ended the Permian and ushered in the Mesozoic, the Triassic, and the dinosaurs in one big bang. This isn’t a novel finding, and there has been interest in this spot as a crater since the 1970s (per Wikipedia). No one knows how old it is, either. It could be the source for the Australasian strewnfield of tektite debris, but that’s only 790,000 years old (per Wikipedia).
Of course, the object’s under an ice sheet, so until the ice sheet goes away, we’re stuck with some really stupendous drilling to get into it and see what it is. After the ice goes away, well, there may not be scientists interested in studying it.
Still, there’s an interesting issue here, about mass extinctions and the paucity of evidence. For one thing, there is some evidence of a meteorite/asteroid strike around the time of the P-T, but there’s no good evidence, and that’s fairly important. There’s no P-T iridium layer, or worldwide shocked quartz, or tektites. Indeed, there’s little worldwide left from P-T times at all. There is evidence of fairly radical shifts in atmospheric and oceanic chemistry, but they could have had terrestrial causes.
Then there’s the whole problem with asteroid strikes. Don Prothero laid this out years ago in After The Dinosaurs. There are a lot of craters on Earth, but only a couple (Sudbury in Canada and Vredefort in South Africa) that are bigger than Chicxulub, and both of these are well over a billion years old. We’ve got pretty good evidence that the Chicxulub strike was a very bad day for Earth, so we tend to think of asteroids as mass extinction bullets (well, bolides, technically). The problem is, when you look at all the smaller craters that dot Earth (and there are quite a few), none of them are unambiguously associated with extinction events at any scale. There may have been disruptions, but life afterward went back to the way it was before. This pattern led Prothero to speculate that the biosphere’s response curve in terms of species extinctions as a function of rock size is very non-linear, and that when you drop much below Chicxulub-sized bolides, there are few if any extinctions, at least of the kind (like coral reef dieoffs) that tend to leave behind a good fossil trace. The trouble is, the sample size for the bigger craters is basically one (Chicxulub), so this curve is speculative. Sudbury and Vredefort are bigger, but they occurred back before multicellular life is known to have evolved. They may have caused mass microbial extinctions, but there’s no fossil record of it.
That’s why whatever is under the ice is so important. If it does turn out to be a crater, and it does turn out to be the trilobite buster from the P-T mass extinction, then we have to re-think our models of the damage caused by climate change. Right now, we climate-freaks tend to think of mass extinction from a anthropogenic climate change (or as I call it, the terafart) as falling somewhere between the PETM Paleocene-Eocene extinction event (which is thought to be the equivalent of what we’re heading into) and the Permian-Triassic megadeath concert, when the air became impossible for mammals to breathe a kilometer above sea level. The idea behind the latter is that the rather enormous Siberian Traps volcanoes fertilized the sea, promoted massive growth of methanogenic bacteria, which made the ocean anoxic and blew out so much methane/CO2 that atmospheric oxygen concentrations plummeted, thereby wiping out much of life in a really ugly hothouse world.
Now, if it turns out that the P-T also had a big bolide strike at the critical moment, then we’re looking at a different pattern. See, the end Cretaceous (K-Pg) Chicxulub strike happened when the Deccan Traps were erupting, and dinosaur species had already been going extinct for hundreds of thousands of years before the Chicxulub asteroid killed all the non-birds. If it turns out that the P-T was something similar, with the Siberian Traps making the world miserable before a doubleplus big rock made it almost uninhabitable, then that suggests that climate change isn’t the major driver of mass extinctions that we thought it was. This doesn’t mean that climate change is a good thing, it’s just that it might not cause mass extinctions. It’s more like it causes medium-sized extinctions, possibly with a side of civilization collapse. To get up to mass extinction event, you need a big asteroid as well as massive atmospheric composition change.
But this is all speculation of the most uninformed kind. We don’t know much about the Wilkes Land gravity anomaly other than that it exists. It’s bisected by a 100 million year-old rift zone (apparently), so it’s apparently an old structure. But no one has drilled into it and tried to date it, at least to my knowledge. If I had to bet, I’d guess that it’s considerably older than the P-T, but you never know. Either way, working on it will add some cool new, relevant science, so hopefully someone will get a drill rig down there and get some real samples.
But maybe we don’t need a bolide. After all, if we upgrade our nuclear arsenals enough, perhaps we can cause devastation equivalent to Chicxulub. That, with climate change, really could lead to a mass extinction event. Has anybody listened for a whistled tekelili around capitol cities or military bases recently?
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