Seth Burgess has, literally, travelled to the ends of the Earth to find a date. Along the way he has endured attacks of giant flesh-eating bee-flies, paddled a raft 60 miles in driving Siberian rain, braved volcanoes in Alaska, and inhaled polluted air in China for weeks on end, all the while hauling pounds of rocks. And all in the name of Science.
The date he seeks plays extremely hard to get.
In Siberia, Seth and his colleagues whacked off rocks from cliffs in dozens of mosquito-infested riverbanks scattered across over a thousand miles of Siberia, and hauled them back to MIT in Massachusetts. He pulverized his rocks to free tiny zircon crystals and then baked them before bathing them in ultra-pure hydrofluoric acid (an acid so powerful that it dissolves glass) for two days. He then took his cleaned-up gems to the University of Arizona, where he inspected each and every tiny grain under a microscope and then zapped it with a laser and sucked the vapor into a machine called a “LaserChron.”
Sadly, not a single gem was worthy.
“So all that work really for naught!” Seth told me when I met him in the American Geophysical Union meeting in San Francisco in December.
The date Seth was pursuing was the age of the most cataclysmic event to hit the Earth since animals evolved. No, not the end-Cretaceous when the dinosaurs were annihilated, a much bigger catastrophe even than that: the end-Permian mass extinction, when more than 90% of species ceased to exist. It was a time when severe global warming made oceans as hot as the legal limit of a hot tub, and gasses from Siberian volcanic eruptions were the suspected culprit. To convict the eruptions, Seth needed to see if they occurred just before the mass extinction, at a precision never before achieved.
Obviously it makes sense if you want to date the onset of the eruption and tie that time in Earth history to when the mass extinction occurred, you want to date the first stuff to erupt.
But that stuff formed so explosively that it’s now a jumble of volcanic ash and shattered sediments, and unfortunately for Seth it turns out that those sediments brought with them all those unworthy zircons. Seth told me,
There were zircons that ranged in age from about 260 million years old to 2.5 billion. It’s just a hodge-podge of stuff.
Undeterred, Seth moved on to find a date for the 2 ½-mile-thick, thousand-mile-wide layer cake of the Siberian lavas. But the lavas had no zircons, so he had to settle for perovskite crystals instead.
So we had to go to kind of like the ugly stepsister. But in the absence of the cute sister maybe the ugly sister is not so bad! You’re hard up, so that’s where you’ve got to go!
To cut a long story short, Seth did get his date – several in fact. Some of them were actually from zircons extracted from volcanic ash he found sandwiched between layers of lava.
And what those dates proved was that an unconscionable quantity of lava erupted in what geologists call a ridiculously short period of time – about 300,000 years or less - and yes, right before the mass extinction. The eruptions delivered a huge slug of greenhouse gas to the atmosphere, far more than humans could even if we were to burn all our fossil fuels, which explains the hot tub ocean temperatures. The eruptions were so relentless that there wasn’t any time for soil to develop between lava flows.
It’s a similar story in Antarctica, where lavas of the “Ferrar Large Igneous Province” have been tied to a minor (but still global) mass extinction known as the Toarcian Extinction.
Every single rock I dated from the Ferrar, and we’re talking up the mountain, down in the ravine, from one side of the continent to the other, along the Transantarctic Mountains - they’re all 182.6 million years old! It’s every single rock the same! And we’ve already talked about how much work it is to date one frigging rock! And when I date 22 of them and they’re the same age, and they’re from all over the place in the Transantarctic Mountains it gives me a great sense of: it’s all in one shot! It’s not a big slow prolonged event.
Seth’s dating quest, and similar travails by other geochronologists, have now proven the close link in time between several mass extinctions in Earth’s past and huge eruptions, including for the end-Cretaceous extinction that wiped out the dinosaurs. In that example geochronologists have tied the famous Chicxulub asteroid impact date to the same time as gargantuan eruptions in India, suggesting that the impact may have aggravated the eruptions. So it seems the dinosaurs were extinguished by the original “double whammy.”
Posted by howardlee on Monday, 15 February, 2016
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