Exploring Extinction: An Interview with Gerta Keller
Dr Gerta Keller is a paleontologist and geologist, and has been Professor of Geosciences at Princeton University since 1984. Her main area of interest is the Cretaceous-Tertiary (K-T) extinction, which killed off the last non-avian dinosaurs and countless other creatures around 66 million years ago. She has co-authored numerous papers and several books on the subject, and been featured on relevant television programs like What Really Killed the Dinosaurs (BBC, 2004) and First Apocalypse (History Channel, 2008). Rather than an object from space, Keller believes that volcanoes in India were the real culprit behind the extinction.
I met with her recently at Princeton to discuss getting into geology, past and possible future eruptions, and overlooked organisms and extinctions.
What sparked your interest in paleontology and geology?
It's a long story...let's make it short: I studied anthropology as an undergraduate, but felt it wasn't quite for me. It was too controversial -- sounds silly, in retrospect. I took a class called "Man and the Ice Age". It was quite interesting and I asked the professor why he became a geologist and paleontologist, and he said, "If you like rocks and fossils and like to travel and spend time at the beach, you should join geology."
"That's good enough for me," I said. "I'll try it." And it has worked.
Once I got into geology, I became interested in paleontology as well, particularly mass extinctions.
What’s been the biggest surprise during your career in these sciences?
The biggest surprise is how contentious the fields are. Lots of infighting.
How have advances in technology directly affected your work?
Hugely. I started off pre-computers, so you could talk to people on the phone, but that would get expensive. Now you can communicate around the world for nothing. That's made a tremendous difference because now you can collaborate with any scientist as if they were next door.
Many paleontologists in the 1980s were outraged when physicist Luis Alvarez and geologist son Walter posited that a huge comet wiped out the dinosaurs around 66 million years ago. What was your gut reaction to this hypothesis?
"Fantastic." Fantastic, but not entirely in a good sense. "It's a fantastic idea, but is it true?"
I was just about to study the K-T (Cretaceous-Tertiary) extinction when I learned about it, and I thought, "Oh well, there's no way I'm gonna start now, there's all this controversy."
So I waited for five years, and the controversy still hadn't died down, and it's still going on now.
The Chicxulub crater off the coast of the Yucatán Peninsula is now generally regarded at the site of impact. Yet you’ve proposed that volcanic activity in India played a greater role in this mass extinction than the comet. Would you care to summarize this premise?
I spent the first twenty years trying to convince myself that the Chicxulub impact was the cause. I traveled to areas in North and Central America with undisputed impact evidence [such as glass spherules], looked at the rock layers, and whether the data was there to support it. Virtually everywhere, we found data that didn't. The impact predates the extinction by 100,000 years.
At the same time, I was studying volcanism. If Chicxulub wasn't the reason, there had to be another catastrophe, and that was the Deccan Traps eruptions in India, which started happening about 250,000 years before the K-T boundary. These were humongous eruptions the size of France with lava flows 3 km (1.9 mi) deep. They released greenhouse gases like carbon dioxide, sulfur dioxide, and chlorine into the atmosphere, causing rapid global warming and acid rain. The center of the eruptions was near Mumbai, but they extended 1,500 km (932 mi) east to the Bay of Bengal.
According to high resolution age dating, 80 percent of those eruptions took place over approximately 700,000 years. But 80 percent of that amount happened within just 200,000. How deadly volcanic eruptions are depends on how fast gases are injected into the environment. If they occur infrequently, then the environment can recover between eruptions. But if they happen this often and this rapidly, the environment will never equilibrate. There would have been extreme warming and acid rain on land and the oceans would have been acidified. If the species there can't produce their calcium carbonate shells, that's it. The whole marine food chain collapses.
The rock record of northeastern Mexico shows no lasting effects on these microorganisms from the Chicxulub impact.
Are there any places in the world where something similar could happen in the future? Yes, Yellowstone. Eruptions could happen there not that far in the future and it would be very destructive. But not in our lifetime.
How have other scientists received this scenario?
Many scientists believe the impact theory as you believe in God, but today, they're starting to come around.
All the major geology conferences since 2013 have addressed Deccan volcanism and mass extinctions. The Berkeley group were the first to modify the impact theory and take the Deccan Traps into account. Since then, Paul Renne and others have proposed that the impact triggered the eruptions that likely caused the mass extinctions. They have been visiting India every year and writing variations on this same theme.
However, no geophysicist believes this. There are more papers than ever on various aspects of Deccan volcanism, and more and more people are jumping on the Deccan bandwagon.
A lot of your work on this subject has focused on foraminifera, aquatic microorganisms you mentioned earlier and which don’t get a lot of attention. What are they like and how were they impacted by this extinction?
Foraminifera -- or "forams" -- are the smallest animals. One cell only. And yet, they tell us what the environment was like as far back as 250 million years ago. They develop these very intricate calcium carbonate shells and every species has its own design, which is determined by its environment. It's not surprising, then, that they're so sensitive to environmental changes. The largest, most ornamented species get knocked out the quickest. Omnivorous ones can adjust to changes in temperature, oxygen, and salinity and do best under stressful conditions.
All but one went extinct during the Cretaceous-Tertiary extinction: Guembelitria cretacea. It's a disaster opportunist that dwindles when conditions improve, but never dies. It survives today near the surface and thrives during ocean acidification. It's like a cockroach.
You’ve also studied lesser-known extinction events and ancient incidents of climate change. Could you tell us a bit about these events and what you and your colleagues have found?
The Cenomanian-Turonian extinction [about 90 million years ago] was global and caused by volcanism, but it was caused by submarine volcanism, which tends not to be as deadly as continental volcanism because no greenhouse gases get into the atmosphere.
The Paleocene-Eocene Thermal Maximum [55 million years ago] also interests me. It started with North Atlantic volcanic eruptions, which caused ocean temperatures to rise 3 or 4 degrees Celsius, accompanied by ocean acidification. About 40 percent of deep-sea forams went extinct, but just as many new ones evolved, just like during the Cenomanian-Turonian extinction.
How do you hope your findings will help change public opinion about extinction in general?
I hope that they will realize that simple answers are not usually the right ones, because the world is a complex system. A one-hit wonder like the Chicxulub impact is a highly unlikely explanation for something as complex as a mass extinction that delayed the planet's recovery for half a million years afterwards.