By looking backward at the course of great extinctions, a paleontologist sees what the future holds.
More than 200 million years ago, a cataclysmic event known as the Permian extinction destroyed more than 90 percent of all species and nearly 97 percent of all living things. Its origins have long been a puzzle for paleontologists. During the 1990s and the early part of this century, a great battle was fought between those who thought that death had come from above and those who thought something more complicated was at work.
Paleontologist Peter. D. Ward, fresh from helping prove that an asteroid had killed the dinosaurs, turned to the Permian problem, and he has come to a stunning conclusion. In his investigations of the fates of several groups of mollusks during that extinction and others, he discovered that the near-total devastation at the end of the Permian period was caused by rising levels of carbon dioxide leading to climate change. But it's not the heat (nor the humidity) that's directly responsible for the extinctions, and the story of the discovery of what is responsible makes for a fascinating, globe-spanning adventure.
In Under a Green Sky, Ward explains how the Permian extinction as well as four others happened, and describes the freakish oceans—belching poisonous gas—and sky—slightly green and always hazy—that would have attended them. Those ancient upheavals demonstrate that the threat of climate change cannot be ignored, lest the world's life today—ourselves included—face the same dire fate that has overwhelmed our planet several times before.
Welcome to the Revolution!
Zumaya, Spain, July 1982
A warm but wet wind from the sea, a wind pushing gray scudding clouds onshore from the squall-torn Bay of Biscay greeted the two geologists as they slowly drove through the narrow, building-lined streets of a small, tiled Basque town named Zumaya, in the quiet of an early Sunday morning. Their knees were still cramped from the daylong drive of the day before, when they had crossed the neck of France by a route that began on the sun-kissed Mediterranean coast at Banyuls-sur-Mer in the Languedoc region, then clung to the edges of the rugged Pyrénées Mountains for their entire south to north length before ending late that night at a cavernous and gloomy hotel perched on the stormy Atlantic Ocean coast in the Basque city of San Sebastián, Spain.
One of the two was Jost Wiedmann, a famous German paleontologist from Tübingen University, itself the most famous and storied paleontological center in the world. He had spent his career studying the geological ranges of one particular group of fossils, one of the most celebrated of all fossil groups, the ammonite cephalopods. He practiced the standard methodology of his German predecessors: studying the collection of the fossils from known locations in strata to produce a "biostratigraphy," literally the differentiation of the many great piles of sedimentary or layered rock so prodigiously scattered across Earth's crust. His particular interest was mass extinction, those short-term biotic catastrophes that were the most dramatic bookmarks in the tables of strata. He had spent much of his fieldwork among the strata of the Cretaceous period making up the fabulously beautiful coastline of France and Spain known as the Basque Country, a place inhabited by a dour race still wishing to be known as a country separate from either France or Spain.
Wiedmann had published widely reports that the ammonites showed no evidence of a rapid extinction but of something quite different. In a number of famous papers that had been published in journals read not just by the small band of professional paleontologists but also by a far wider spectrum of geologists and evolutionary biologists, Wiedmann had presented evidence that the final extinction of the ammonites was the final act of a long, slow diminution of diversity that had lasted more than 20 million years. By the end, almost none were left anyway, making the K-T event (an event straddling the Cretaceous and Tertiary periods) a minor extinction at best—at least for the ammonites.
I was the other member here, at that time a young American from the University of California, Davis, one of the new breed of American scientists who styled themselves as "paleobiologists," not one of the paleontologists of old, in an effort to bring new intellectual vibrancy into the oldest field of Earth science, paleontology, by trying to master two fields, not just one. I had completed two quite different research projects for my still rather newly minted Ph.D., the central goal of which was an attempt to understand how the long-extinct ammonite cephalopods could, after a wildly successful existence on Earth of more than 360 million years, would have gone extinct, while their nearest, lookalike relatives, the still living chambered nautilus, had escaped that fate at the end of the Cretaceous period. I had approached this topic from two different directions, one very nontraditional. The old-school approach was the study of the fossils themselves: anything defective here, any morphology antiquated there, as I examined fossil after fossil over a 20-million-year period prior to their final extinction? Actually, pretty boring work. But the other was a very different approach. Long a deep-water salvage diver of professional skill and experience, I had through chance and fortitude talked my way into a research grant that took me to the one place on Earth where a living nautilus could be actually seen in the wild, the island of New Caledonia, some 700 miles east of the Great Barrier Reef region of Australia. Since that four-month expedition in 1975, I had managed to spend at least a month each year in the water with the wild nautilus and by this time in 1982 had expanded my study area to include Fiji, and I was anticipating with enormous excitement my 1983 field season, already planned for Palau, Micronesia, home to the largest nautiluses (and most beautiful reef walls) in the world. Even the cuttlefish there were giant.
In those years, work with the nautilus was directed by questions that more traditional biologists had never asked of this oldest of cephalopod mollusk, ones that hopefully could shed light on the life span, growth rate, food, and predators of the nautilus that might through inference inform about the ammonites as well, and year by year I arrived in the sunny tropics with better equipment, more grant money, and new ideas and colleagues. But this side of my scientific schizophrenia was increasingly shoving aside geological pursuits, and my presence in Europe in the summer of '82 was not to study fossil ammonites but to look at another living cephalopod that might lend insight into the ammonites, a squidlike animal known as the cuttlefish. This work had drawn me to France, and it was a sheer accident that a chance letter to Wiedmann had led to this invitation to visit one of the few sites on Earth where fossil ammonites could be found in stratigraphic sections with both youngest Cretaceous and oldest Tertiary found in a continuous and well-exposed outcrop.
Wiedmann was definitely old school, a classically trained paleontologist. Sadly enough for the field, by the middle of the twentieth century when Wiedmann had trained in the carnage and chaos of immediate postWorld War II Germany, the discipline of paleontology, once a vibrant and necessary area of science important in the study of evolution, had become a sleepy enclave whose every practitioner could spend an entire career writing detailed monographs about the slight differences to be . . .