When scientists first suggested in the early 1980s that volcanic activity had wiped out most dinosaurs 66 million years ago, Paul Olsen wasn’t having any of it. He wasn’t even convinced there had been a mass extinction.
Olsen, a paleontologist and geologist at Columbia University, eventually came to accept the idea of mass extinctions. He also acknowledged that volcanoes played a role in certain extinction events. But even then, he wasn’t entirely convinced about the cause of these extinctions.
The leading hypothesis holds massive eruptions blasted carbon dioxide into Earth's atmosphere, cranking up global temperatures within a relatively short period of time. Such a sudden change, the theory goes, would have killed off terrestrial species like the huge ancestors of crocodiles and large tropical amphibians and opened the door for dinosaurs to evolve.
Olsen, who discovered his first dinosaur footprint in the 1960s as a teenager in New Jersey and still uses the state’s geological formations to inform his work, wondered whether something else may have been at work—such as sudden cooling events after some of these eruptions, rather than warming.
It's an idea that's been around in some form for decades, but the 63-year-old Olsen is the first to strongly argue that sulfate aerosols in the atmosphere could have been responsible for the cooling. A sudden chill would explain the selective nature of the extinctions, which affected some groups strongly and others not at all.
His willingness to revive an old debate and look at it from a fresh angle has earned Olsen a reputation as an important voice in the field of earth sciences.
From the moment Olsen abandoned dreams of becoming a marine biologist as a scrawny teenager and fell in love with dinosaurs, he courted controversy and earned a reputation for making breathtaking discoveries.
Olsen’s first breakthrough came as a young teen, when he, his friend Tony Lessa and several other dinosaur enthusiasts discovered thousands of fossilized footprints at a quarry near his house in Rosemount, New Jersey. They were the remnants of carnivorous dinosaurs and tiny crocodile relatives that dated back to the Jurassic, 201 million years ago. The teens' efforts to successfully designate the quarry as a dinosaur park inspired a 1970 Life magazine article.
Olsen even sent a letter to President Richard Nixon urging his support for the park, and followed that with a cast of a dinosaur footprint. "It is a miracle that nature has given us this gift, this relic of the ages, so near to our culturally starved metropolitan area," the young Olsen wrote in a later letter to Nixon. "A great find like this cannot go unprotected and it must be preserved for all humanity to see." (Olsen eventually received a response from the deputy director of the Interior Department's Mesozoic Fossil Sites Division.)
Olsen shook things up again as an undergraduate student at Yale. In this case, he and Peter Galton published a 1977 paper in Science that questioned whether the end-Triassic mass extinction had even happened, based on what he called incorrect dating of the fossils. Subsequent fossil discoveries showed that Olsen was wrong, which he readily acknowledged.
In the 1980s, Olsen demonstrated that Earth’s orbital cycles—the orientation of our planet on its axis and the shape of its path around the sun—influenced tropical climates and caused lakes to come and go as far back as 200 million years ago. It was a controversial idea at the time, and even today has its doubters.
More recently, Olsen and colleagues dated the Central Atlantic Magmatic Province—large igneous rock deposits that were the result of massive volcanic eruptions—to 201 million years ago. That meant the eruptions played a role in the end-Triassic mass extinction. They published their results in a 2013 study in the journal Science.
But it is his latest project—reexamining the causes of mass extinctions—that could be his most controversial yet.
Researchers generally recognize five mass extinction events over the past 500 million years, Olsen explains. We may be in the middle of a sixth event right now, which started tens of thousands of years ago with the extinction of animals like the mastodon.
Determining the causes and timing of these extinctions is incredibly difficult. Regardless of cause, however, these events can pave the way for whole new groups of organisms. In fact, the disappearance of nearly all synapsids—a group that includes mammals and their relatives—in the Triassic may have allowed for the evolution of dinosaurs about 230 million years ago.
The accepted theory for the end-Triassic extinction states that gases from enormous volcanic eruptions led to a spike in carbon dioxide levels, which in turn increased global temperatures by as much as 11 degrees F. Terrestrial species, like the huge ancestors of crocodiles and large tropical amphibians, would have perished because they couldn't adapt to the new climate.
However, this explanation never sat well with Olsen. “If we are back in the time of the Triassic and the dominant life forms on land are these crocodile relatives, why would a three degree [Celsius] increase in temperature do anything?” asks Olsen, sitting in his office on the campus of Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York.
Some inland tropical areas would have become lethally hot, Olsen says, surrounded by fossils, dinosaur memorabilia and a Nixon commendation on the wall. But the mountains and coastlines would still be bearable. "It’s hard to imagine the temperature increase would be a big deal,” he says.
Three years ago, Olsen began looking at the fossil record of species that survived other mass extinctions, like the Cretaceous-Tertiary (K-T) event 66 million years ago and the Permian event roughly 250 million years ago. What he saw suggested a completely different story: Earth's climate during and after these volcanic eruptions or asteroid impacts got briefly but intensely cold, not hotter, as volcanic ash and droplets of sulfate aerosols obscured the sun.
Scientists generally agree that the reduced sunlight would have disrupted photosynthesis, which plants need to survive. During the K-T extinction event, plant losses would have left many herbivorous dinosaurs, and their predators, with little to eat.
In this case, size became the determining factor in whether a species went extinct. Large animals need more food than smaller animals to survive, Olsen explains.
With his fluffy white mustache and hearty laugh, Olsen is hard to miss at paleontology meetings. He's not afraid to insert himself into mass extinction debates, but is quick to point out that he counts even his most ardent critics among his friends.
Supporters praise his creativity, persistence and willingness to consider the big unanswered questions in paleontology that, if solved, would alter our understanding of important events like mass extinctions.
“Among academics, you see two types. You see the parachutists and you see the truffle hunters, and Paul is a parachutist,” says Hans Sues, chairman of the department of paleobiology at the Smithsonian National Museum of Natural History. “The parachutist is the one who helps build the big frame in which other people operate.” Sues and Olsen, who have pieced together fossils in the past, have known each other for 30 years.
Olsen's latest project—the volcanic winter theory—has him looking for ancient ash deposits from the United States to Morocco to the United Kingdom. He hopes to find the fingerprints of certain sulfur isotopes and metals that could indicate that sulfur-rich super-eruptions occured. They would also pinpoint the timing of the eruptions relative to the extinctions, Olsen explains.
Evidence of ancient ice would also bolster his case. For those clues, Olsen must look to mud flats laid down in what would have been the tropics—some of which are in areas in New Jersey, where he searched for dinosaurs as a teenager. “If you find these little crystals on mud flats, you know it froze in the tropics," Olsen says.
Sues is among those who believe Olsen’s hypothesis has merit, partly because Olsen is focused on the sulfate aerosols from eruptions. In the recent past, massive volcanic eruptions—like Mount Pinatubo in 1991—belched the sulfate aerosols into the atmosphere, which reduced global temperatures. The trick is finding evidence of extreme cold in rocks, Sues says.
But other scientists, like Spencer G. Lucas, curator of paleontology at the New Mexico Museum of Natural History and Science, have their doubts.
As someone who has long sparred with Olsen on mass extinctions, Lucas agrees that volcanism played a role in extinctions and isn’t ruling out cooling as the cause. But finding chemical evidence of that in the rocks or preserved ash will be difficult, if not impossible, to find, he says.
Searching for those clues isn't a waste of time though, says Lucas. He wants someone who cares about the problem, like Olsen, to collect the evidence and makes a convincing case for the Earth either cooling or warming during these extinctions.
“Paul is sort of the Don Quixote of extinctions,” Lucas says. “He is tilting at a windmill in my mind. But I’m glad he’s doing it because he knows he has got the background, the smarts and the opportunity. If anybody can figure this out, he will.”