The Best American Science and Nature Writing 2020

by Michio Kaku

  Today, the layer of debris, ash, and soot deposited by the asteroid strike is preserved in the Earth’s sediment as a stripe of black about the thickness of a notebook. This is called the KT boundary, because it marks the dividing line between the Cretaceous period and the Tertiary period. (The Tertiary has been redefined as the Paleogene, but the term “KT” persists.) Mysteries abound above and below the KT layer. In the late Cretaceous, widespread volcanoes spewed vast quantities of gas and dust into the atmosphere, and the air contained far higher levels of carbon dioxide than the air that we breathe now. The climate was tropical, and the planet was perhaps entirely free of ice. Yet scientists know very little about the animals and plants that were living at the time, and as a result they have been searching for fossil deposits as close to the KT boundary as possible.

  One of the central mysteries of paleontology is the so-called “three-meter problem.” In a century and a half of assiduous searching, almost no dinosaur remains have been found in the layers three meters, or about nine feet, below the KT boundary, a depth representing many thousands of years. Consequently, numerous paleontologists have argued that the dinosaurs were on the way to extinction long before the asteroid struck, owing perhaps to the volcanic eruptions and climate change. Other scientists have countered that the three-meter problem merely reflects how hard it is to find fossils. Sooner or later, they’ve contended, a scientist will discover dinosaurs much closer to the moment of destruction.

  Locked in the KT boundary are the answers to our questions about one of the most significant events in the history of life on the planet. If one looks at the Earth as a kind of living organism, as many biologists do, you could say that it was shot by a bullet and almost died. Deciphering what happened on the day of destruction is crucial not only to solving the three-meter problem but also to explaining our own genesis as a species.

  * * *

  On August 5, 2013, I received an email from a graduate student named Robert DePalma. I had never met DePalma, but we had corresponded on paleontological matters for years, ever since he had read a novel I’d written that centered on the discovery of a fossilized Tyrannosaurus rex killed by the KT impact. “I have made an incredible and unprecedented discovery,” he wrote me, from a truck stop in Bowman, North Dakota. “It is extremely confidential and only three others know of it at the moment, all of them close colleagues.” He went on, “It is far more unique and far rarer than any simple dinosaur discovery. I would prefer not outlining the details via email, if possible.” He gave me his cell-phone number and a time to call.

  I called, and he told me that he had discovered a site like the one I’d imagined in my novel, which contained, among other things, direct victims of the catastrophe. At first, I was skeptical. DePalma was a scientific nobody, a PhD candidate at the University of Kansas, and he said that he had found the site with no institutional backing and no collaborators. I thought that he was likely exaggerating, or that he might even be crazy. (Paleontology has more than its share of unusual people.) But I was intrigued enough to get on a plane to North Dakota to see for myself.

  DePalma’s find was in the Hell Creek geological formation, which outcrops in parts of North Dakota, South Dakota, Montana, and Wyoming, and contains some of the most storied dinosaur beds in the world. At the time of the impact, the Hell Creek landscape consisted of steamy, subtropical lowlands and floodplains along the shores of an inland sea. The land teemed with life and the conditions were excellent for fossilization, with seasonal floods and meandering rivers that rapidly buried dead animals and plants.

  Dinosaur hunters first discovered these rich fossil beds in the late nineteenth century. In 1902, Barnum Brown, a flamboyant dinosaur hunter who worked at the American Museum of Natural History, in New York, found the first Tyrannosaurus rex here, causing a worldwide sensation. One paleontologist estimated that in the Cretaceous period Hell Creek was so thick with T. rexes that they were like hyenas on the Serengeti. It was also home to triceratops and duckbills.

  The Hell Creek Formation spanned the Cretaceous and the Paleogene periods, and paleontologists had known for at least half a century that an extinction had occurred then, because dinosaurs were found below, but never above, the KT layer. This was true not only in Hell Creek but all over the world. For many years, scientists believed that the KT extinction was no great mystery: over millions of years, volcanism, climate change, and other events gradually killed off many forms of life. But, in the late 1970s, a young geologist named Walter Alvarez and his father, Luis Alvarez, a nuclear physicist, discovered that the KT layer was laced with unusually high amounts of the rare metal iridium, which, they hypothesized, was from the dusty remains of an asteroid impact. In an article in Science, published in 1980, they proposed that this impact was so large that it triggered the mass extinction, and that the KT layer was the debris from that event. Most paleontologists rejected the idea that a sudden, random encounter with space junk had drastically altered the evolution of life on Earth. But as the years passed the evidence mounted, until, in a 1991 paper, the smoking gun was announced: the discovery of an impact crater buried under thousands of feet of sediment in the Yucatán peninsula, of exactly the right age, and of the right size and geochemistry, to have caused a worldwide cataclysm. The crater and the asteroid were named Chicxulub, after a small Mayan town near the epicenter.

  One of the authors of the 1991 paper, David Kring, was so frightened by what he learned of the impact’s destructive nature that he became a leading voice in calling for a system to identify and neutralize threatening asteroids. “There’s no uncertainty to this statement: the Earth will be hit by a Chicxulub-size asteroid again, unless we deflect it,” he told me. “Even a three-hundred-meter rock would end world agriculture.”

  In 2010, forty-one researchers in many scientific disciplines announced, in a landmark Science article, that the issue should be considered settled: a huge asteroid impact caused the extinction. But opposition to the idea remains passionate. The main competing hypothesis is that the colossal “Deccan” volcanic eruptions, in what would become India, spewed enough sulfur and carbon dioxide into the atmosphere to cause a climatic shift. The eruptions, which began before the KT impact and continued after it, were among the biggest in Earth’s history, lasting hundreds of thousands of years, and burying half a million square miles of the Earth’s surface a mile deep in lava. The three-meter gap below the KT layer, proponents argued, was evidence that the mass extinction was well under way by the time of the asteroid strike.

  * * *

  In 2004, DePalma, at the time a twenty-two-year-old paleontology undergraduate, began excavating a small site in the Hell Creek Formation. The site had once been a pond, and the deposit consisted of very thin layers of sediment. Normally, one geological layer might represent thousands or millions of years. But DePalma was able to show that each layer in the deposit had been laid down in a single big rainstorm. “We could see when there were buds on the trees,” he told me. “We could see when the cypresses were dropping their needles in the fall. We could experience this in real time.” Peering at the layers was like flipping through a paleo-history book that chronicled decades of ecology in its silty pages. DePalma’s adviser, the late Larry Martin, urged him to find a similar site, but one that had layers closer to the KT boundary.

  Today, DePalma, now thirty-seven, is still working toward his PhD. He holds the unpaid position of curator of vertebrate paleontology at the Palm Beach Museum of Natural History, a nascent and struggling museum with no exhibition space. In 2012, while looking for a new pond deposit, he heard that a private collector had stumbled upon an unusual site on a cattle ranch near Bowman, North Dakota. (Much of the Hell Creek land is privately owned, and ranchers will sell digging rights to whoever will pay decent money, paleontologists and commercial fossil collectors alike.) The collector felt that the site, a three-foot-deep layer exposed at the surface, was a bust: it was packed with fish fossils, but they were so delicate that they crumbled
into tiny flakes as soon as they met the air. The fish were encased in layers of damp, cracked mud and sand that had never solidified; it was so soft that it could be dug with a shovel or pulled apart by hand. In July 2012, the collector showed DePalma the site and told him that he was welcome to it.

  “I was immediately very disappointed,” DePalma told me. He was hoping for a site like the one he’d excavated earlier: an ancient pond with fine-grained, fossil-bearing layers that spanned many seasons and years. Instead, everything had been deposited in a single flood. But as DePalma poked around he saw potential. The flood had entombed everything immediately, so specimens were exquisitely preserved. He found many complete fish, which are rare in the Hell Creek Formation, and he figured that he could remove them intact if he worked with painstaking care. He agreed to pay the rancher a certain amount for each season that he worked there. (The specifics of the arrangement, as is standard practice in paleontology, are a closely guarded secret. The site is now under exclusive long-term lease.)

  The following July, DePalma returned to do a preliminary excavation of the site. “Almost right away, I saw it was unusual,” he told me. He began shoveling off the layers of soil above where he’d found the fish. This “overburden” is typically material that was deposited long after the specimen lived; there’s little in it to interest a paleontologist, and it is usually discarded. But as soon as DePalma started digging he noticed grayish-white specks in the layers which looked like grains of sand but which, under a hand lens, proved to be tiny spheres and elongated droplets. “I think, Holy shit, these look like microtektites!” DePalma recalled. Microtektites are the blobs of glass that form when molten rock is blasted into the air by an asteroid impact and falls back to Earth in a solidifying drizzle. The site appeared to contain microtektites by the million.

  As DePalma carefully excavated the upper layers, he began uncovering an extraordinary array of fossils, exceedingly delicate but marvelously well preserved. “There’s amazing plant material in there, all interlaced and interlocked,” he recalled. “There are logjams of wood, fish pressed against cypress-tree root bundles, tree trunks smeared with amber.” Most fossils end up being squashed flat by the pressure of the overlying stone, but here everything was three-dimensional, including the fish, having been encased in sediment all at once, which acted as a support. “You see skin, you see dorsal fins literally sticking straight up in the sediments, species new to science,” he said. As he dug, the momentousness of what he had come across slowly dawned on him. If the site was what he hoped, he had made the most important paleontological discovery of the new century.

  * * *

  DePalma grew up in Boca Raton, Florida, and as a child he was fascinated by bones and the stories they contained. His father, Robert Sr., practices endodontic surgery in nearby Delray Beach; his great-uncle Anthony, who died in 2005, at the age of a hundred, was a renowned orthopedic surgeon who wrote several standard textbooks on the subject. (Anthony’s son, Robert’s cousin, is the film director Brian De Palma.)

  “Between the ages of three and four, I made a visual connection with the gracefulness of individual bones and how they fit together as a system,” DePalma told me. “That really struck me. I went after whatever on the dinner table had bones in it.” His family buried their dead pets in one spot and put the burial markers in another, so that he wouldn’t dig up the corpses; he found them anyway. He froze dead lizards in ice-cube trays, which his mother would discover when she had friends over for iced tea. “I was never into sports,” he said. “They tried to get me to do that so I would get along with the other kids. But I was digging up the baseball field looking for bones.”

  DePalma’s great-uncle Anthony, who lived in Pompano Beach, took him under his wing. “I used to visit him every other weekend and show him my latest finds,” DePalma said. When he was four, someone at a museum in Texas gave him a fragment of dinosaur bone, which he took to his great-uncle. “He taught me that all those little knobs and rough patches and protrusions on a bone had names, and that the bone also had a name,” DePalma said. “I was captivated.” At six or seven, on trips to Central Florida with his family, he started finding his own fossilized bones from mammals dating back to the Ice Age. He found his first dinosaur bone when he was nine, in Colorado.

  In high school, during the summer and on weekends, DePalma collected fossils, made dinosaur models, and mounted skeletons for the Graves Museum of Archaeology and Natural History, in Dania Beach. He loaned the museum his childhood fossil collection for display, but in 2004 the museum went bankrupt and many of the specimens were carted off to a community college. DePalma had no paperwork to prove his ownership, and a court refused to return his fossils, which numbered in the hundreds. They were mostly locked away in storage, unavailable for public display and enjoyment.

  Dismayed by what he called the “wasteful mismanagement” of his collection, DePalma adopted some unusual collecting practices. Typically, paleontologists cede the curation and the care of their specimens to the institutions that hold them. But DePalma insists on contractual clauses that give him oversight of the management of his specimens. He never digs on public land, because of what he considers excessive government red tape. But, without federal support for his work, he must cover almost all the costs himself. His out-of-pocket expenses for working the Hell Creek site amount to tens of thousands of dollars. He helps defray the expenses by mounting fossils, doing reconstructions, and casting and selling replicas for museums, private collectors, and other clients. At times, his parents have chipped in. “I squeak by,” he said. “If it’s a toss-up between getting more PaleoBond”—​an expensive liquid glue used to hold fossils together—​“or changing the air-conditioning filter, I’m getting the PaleoBond.” He is single, and shares a three-bedroom apartment with casts of various dinosaurs, including one of a Nanotyrannus. “It’s hard to have a life outside of my work,” he said.

  DePalma’s control of his research collection is controversial. Fossils are a big business; wealthy collectors pay hundreds of thousands of dollars, even millions, for a rare specimen. (In 1997, a T. rex nicknamed Sue was sold at a Sotheby’s auction, to the Field Museum of Natural History, in Chicago, for more than $8.3 million.) The American market is awash in fossils illegally smuggled out of China and Mongolia. But in the U.S. fossil collecting on private property is legal, as is the buying, selling, and exporting of fossils. Many scientists view this trade as a threat to paleontology and argue that important fossils belong in museums. “I’m not allowed to have a private collection of anything I’m studying,” one prominent curator told me. DePalma insists that he maintains “the best of both worlds” for his fossils. He has deposited portions of his collection at several nonprofit institutions, including the University of Kansas, the Palm Beach Museum of Natural History, and Florida Atlantic University; some specimens are temporarily housed in various analytical labs that are conducting tests on them—​all overseen by him.

  In 2013, DePalma briefly made news with a paper he published in the Proceedings of the National Academy of Sciences. Four years earlier, in Hell Creek, he and a field assistant, Robert Feeney, found an odd, lumpy growth of fossilized bone that turned out to be two fused vertebrae from the tail of a hadrosaur, a duck-billed dinosaur from the Cretaceous period. DePalma thought that the bone might have grown around a foreign object and encased it. He took it to Lawrence Memorial Hospital, in Kansas, where a CT technician scanned it for free in the middle of the night, when the machine was idle. Inside the nodule was a broken tyrannosaur tooth; the hadrosaur had been bitten by a tyrannosaur and escaped.

  The discovery helped refute an old hypothesis, revived by the formidable paleontologist Jack Horner, that T. rex was solely a scavenger. Horner argued that T. rex was too slow and lumbering, its arms too puny and its eyesight too poor, to prey on other creatures. When DePalma’s find was picked up by the national media, Horner dismissed it as “speculation” and merely “one data point.” He suggested an alternat
ive scenario: the T. rex might have accidentally bitten the tail of a sleeping hadrosaur, thinking that it was dead, and then “backed away” when it realized its mistake. “I thought that was absolutely preposterous,” DePalma told me. At the time, he told the Los Angeles Times, “A scavenger doesn’t come across a food source and realize all of a sudden that it’s alive.” Horner eventually conceded that T. rex may have hunted live prey. But, when I asked Horner about DePalma recently, he said at first that he didn’t remember him: “In the community, we don’t get to know students very well.”

  Without his PhD, DePalma remains mostly invisible, awaiting the stamp of approval that signals the beginning of a serious research career. Several paleontologists I talked to had not heard of him. Another, who asked not to be named, said, “Finding that kind of fossil was pretty cool, but not life-changing. People sometimes think I’m dumb because I often say I don’t have the answers—​we weren’t there when a fossil was formed. There are other people out there who say they do know, and he’s one of those people. I think he can overinterpret.”

  * * *

  After receiving DePalma’s email, I made arrangements to visit the Hell Creek site; three weeks later I was in Bowman. DePalma pulled up to my hotel in a Toyota 4Runner, its stereo blasting the theme to Raiders of the Lost Ark. He wore a coarse cotton work shirt, cargo pants with canvas suspenders, and a suede cowboy hat with the left brim snapped up. His face was tanned from long days in the sun and he had a five-day-old beard.