On the volcanic plateau: Blair Schoene and the dinosaur extinction

A rhesus monkey scampered toward them, but Blair Schoene and Kyle Samperton GS ’15 just shooed it away. They were too excited by a 15-centimeter-tall ash bed containing an uncommonly large amount of zircon, the mineral of interest. Just as they unpacked their pick-axes, they heard a rumbling above them.

An avalanche offset by monkeys isn’t the field experience most geologists expect. After avoiding the landslide, the researchers found a monkey strutting around them while trying to snatch their bags, unaware that the bags contained more rocks than bananas.

Schoene, an Assistant Professor of Geosciences at the University, was scouring the Deccan Traps, an ancient volcanic region in Western India, for a more precise timeline aligning the extinction of dinosaurs with a massive volcanic event that occurred around the same time of the Chicxulub meteorite impact, which is widely thought to have been the primary cause of the mass extinction of dinosaurs. He published this research as “U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction” in the journal Science last month.

“The K-T boundary is inherently interesting, mostly because of the dinosaurs, but also because it’s the most recent mass extinction; it serves as a modern analog,” Schoene explained. “You can also date things much better if they’re younger. With the Deccan Traps, you want to get to a precision of 20 to 30 thousand years.”

Precision is the centerpiece of Schoene’s research. By analyzing ratios of uranium and lead through U-Pb geochronology, he determined that the volcano began its main eruptions roughly 250,000 years before the extinction. For the next 750,000 years, the volcanoes unleashed about 80 to 90 percent of the Deccan Traps’ lava flow.

“You start at the bottom of a pile of rocks and work your way up,” said Schoene, explaining what geochronology is. “It’s similar to flipping through a history book, but one of the differences here is that many of the pages are missing. You have to go to look at a bunch of sections of rock to see how these things piece together — to write the history.”

The Schoene Identity

Geology has become like religion for Schoene. “It relates me to something much larger than myself. It’s humbling to put ourselves in the context of 4.5 billions years,” Schoene said.

Before he attended Colorado College as an undergraduate, however, he was barely aware that geology was a science. But when Schoene took an Introductory Geology class as a freshman, he was instantly intrigued, especially by granites.

“Studying mass extinction is way sexier than studying granites, but I always find myself gravitating back to granites,” Schoene said. “And I don’t know why, maybe because I climbed on them growing up.”

Through his fieldwork in the American Southwest, his interests ballooned into studying the crust’s formation and evolution, through a technique called geochronology. After college, Schoene received his Ph.D. from MIT in 2006 and conducted his post-doctoral research on the Triassic-Jurassic mass extinction at the University of Geneva. He finally joined Princeton in 2009, when he also received funding to create the University’s own geochronology lab, designed as a synthesis of the MIT and Geneva labs’ best elements.

“When I came [to Princeton], there was literally nothing there — the room where the lab currently is was boarded up,” Samperton, a grad student who works with Blair, said. “But Blair said, ‘There’s nothing here now, but in a few years this is going to be the best place to work. If you come here, you can be a part of it.’ That’s when I was sold.”

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Deccan Traps and Dinosaurs

To the untrained eye, the Deccan Traps may seem like a ubiquitous mass of black rocks. Yet as Schoene and his team drove through the chaotic melee of India’s roads, they scanned the plateaus for tiny pipe vesicles, or veins in the basalt indicating the presence of zircon.

Zircon is the ideal “time capsule” for U-Ph geochronology, due to its high uranium and low lead content. But seeing as how pipe vesicles were nonexistent at the site, the team had to change their plan on the fly. They drove for days hopping from one section of the Traps to another, scanning passing mountains for ash beds or weathered soil deposits known as red boles. At times, they walked miles along road cuts looking for slivers of turquoise and red.

“It’s tough to stay sharp when it’s this punctuated type of fieldwork. But it’s also really exciting, because the type of features we’re looking for are very small-scale features. You could literally drive by them and miss them. That’s part of the reason why no one has been able to do the kind of analysis we’ve done,” Samperton said.

Finding these rock beds is only the first step; one basketball-sized rock sample from these flows could contain as little as a 50-micrometer long sample of zircon. “Part of the difficult part of the work is that we don’t actually know if we’re successful until we get back here, crush them up, and see if there’s datable material,” Schoene explained.

To further their research, Schoene returned to India last month looking for the crucial zircon. Now back on campus, over 400 hours of analysis with a thermal ionization mass spectrometer awaits Schoene and his research group.

Future Research

There are still much older flows and micro-paleontological evidence needed to explain Earth’s history. Moreover, critics are abundant, sticking with the common meteorite impact theory.

“In the end, I don’t think we’ll know if the extinction would have happened without the meteorite or volcanic eruption, but they both happened, and they’re both potentially really important,” Schoene said. “I don’t think our study diminishes the role of the meteorite impact, but it gives us much more precise information on what may have been the role of the volcanic events.”

As Schoene explained the science behind the Deccan Traps to me, he gesticulated actively, diagramming lava flows with his hands as though they were right before us. His hands moved restlessly, as though he wanted to jump onto another plane and go back to the field in India right then and there.