Chixculub: cold, darkness and soot did it for dinosaurs (Introduction)

by David Turell @, Wednesday, March 25, 2020, 21:12 (11 days ago) @ David Turell

Another study:

https://www.quantamagazine.org/pincelli-hull-explains-how-an-asteroid-killed-the-dinosa...

"Researchers had long known that the Deccan Traps erupted within a few million years of the asteroid strike. But in 2015, a group based at Princeton University significantly narrowed the timing. They found that the lava began squishing out of the earth only 250,000 years before the impact and continued for 500,000 years afterward. Then last year, they estimated that a major pulse of lava erupted just tens of thousands of years before the strike. (At the same time, a Berkeley group argued instead that a big pulse began right after.)

"It may seem like an obscure chronological feud, but this one matters: If the Deccan Traps released lava and gas just before the asteroid fell, at least some of the subsequent carnage could be attributed to climate change from the volcanoes. “It made me start to think, ‘OK, this is an open question,’” Hull said.

"She didn’t think that for long. Hull went on to lead a global collaboration that, early this year, published a definitive timeline of how the mayhem played out in small ocean fossils. The team tracked changes in global temperature over time. The planet did warm up before the impact, Hull found, but then cooled back down before the asteroid arrived. And while that warming event didn’t seem to correlate to marine extinctions, over 90% of plankton species abruptly vanished after the impact. The study suggests that the major influence of the Deccan Traps was to guide the post-apocalyptic evolution of surviving species — not to drive the extinction itself.

***

"The data we were looking at in this study was actually temperature data. Then we ran a bunch of carbon-cycle models to try and see how can we simulate these temperature records. If you have that volcanism going on before the impact, it has to stop about 200,000 years before [to reproduce the temperatures we see]. And if you look at species, nothing really goes extinct at that time. All the species that have moved to higher latitudes because of the warmth, they’ve moved back down. The ecosystems did respond to this warming that’s probably due to volcanism, but they’ve also come back to their normal baseline before the impact.

"Some mass extinctions that we see in the fossil record potentially played out over hundreds of thousands of years. That’s a different set of mechanisms than in an extinction like the K-T boundary, where we’re arguing it played out over the course of hundreds of years. Hundreds of years is a human timescale. That’s what we’re doing now.

"What the study says is that the K-T extinction is perhaps a really good analogue for today because it’s so, so rapid. We’re not talking about volcanism priming the pump for extinction. Really nasty conditions for a few decades, or a few hundred years, is all it takes.

***

"And on long timescales, the cheerful note is that, as Stephen Jay Gould said, not once since life evolved has it ever gone completely extinct. Life as a whole is pretty tough. But the species that are dominant before a mass extinction, effectively, are almost never the dominant ones afterward. And so that’s extremely sobering. If you’re grumpy at humanity, then you can think, well, somebody else is going to get a chance. I’m fairly hopeful that life goes on, and when life goes on, it does really interesting and creative stuff. So that’s good. But as a human, I care about us, so that’s depressing."

Comment: This study suggests the Chixculub extinction was quick because of the volcanoes adding their contributions.


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