Bad genes or bad luck? That’s the subtitle of Extinction, David Raup’s romp through Earth history from his viewpoint as a preeminent palaeontologist. Raup (along with colleague Jack Sepkoski) became somewhat well known for their theory that extinctions occur in 27-million-year cycles. He accompanied that theory with a related defense of the notion that the sun has a sister star, Nemesis, locked in a binary orbit but as yet undiscovered. In theory, Nemesis’s swing around the sun corresponded with mass extinctions by disturbing the orbit of comets and dwarf planets, which sometimes collided with Earth and caused massive die-offs.
I’ll save my thoughts about the death star Nemesis and Raup’s cyclicity of mass extinctions for a later story, except to say that Nemesis has never been proven. As more and more evidence has been uncovered, it seems less and less likely to exist. However, Raup’s hypothesis that extinctions are regularly occurring at 27-million-year intervals is seen as 99% likely, at least according to a paper from four years ago by Adrian Melott (University of Kansas) and Richard Bambach (Smithsonian Institution Museum of Natural History).
Rather than explore Nemesis and the cycles of extinction, I want to write a few words about David Raup’s 1992 book, Extinction: Bad Genes or Bad Luck. The book is almost 25 years old, but much of the science is still relevant and still (according to most palaeontologists) reasonably accurate. The book is extremely well-written, an easy read, accessible for non-scientists, and (at 200 pages) short enough for most people to finish on a single weekend. Raup, now retired and 81 years old, worked at the University of Chicago and was respected by the likes of Stephen Jay Gould, who wrote the book’s introduction.
One thing that drew me to read Raup’s book is the fact that it was written at the time that collisions of Earth with comets and asteroids was just beginning to be seen as the cause of mass extinctions. It is contemporaneous with the unfolding science of extinction. That alone makes it a valuable insight into the thought processes of players in scientific revolutions.
In 1980, the reformed nuclear physicist Louis Alvarez (et al.) presented the idea that dinosaur extinction 66 million years ago (the K-T, or Cretaceous-Tertiary mass extinction) was due to an asteroid’s impact with the Earth. The proof was a tenuous layer of iridium that marks the boundary between older Cretaceous rocks and younger Tertiary ones. Iridium is rare on our planet, but somewhat common in space rocks. The theory proposed that an iridium-rich meteor ripped into our world, heating and blasting the surface, and smearing its iridium around the world. Scientists have found it at the K-T boundary in New Zealand, Italy, and many points between.
In 1980, the idea that a meteor killed the dinosaurs was greeted with skepticism. Actually, “horror and disbelief” according to David Raup, who added, “It was like suggesting that the dinosaurs had been shot by little green men from a spaceship.” Raup was 60 years old when his book was released in 1992 and he retired shortly after. But he stood in favour of the notion of mass extinction via asteroid/comet impacts. This made him one of the first renowned palaeontologists to agree with the theory. Until then, many saw the idea of a rare catastrophic event as, well, horrific and unbelievable. Remember, geological gradualism held sway for two centuries. Darwin himself had rejected all catastrophic explanations for species extinction, writing:
“. . . we marvel when we hear of the extinction of an organic being; and as we do not see the cause, we invoke cataclysms to desolate the world, or invent laws on the duration of the forms of life! ” – Darwin, Origin of Species, p 73.
Darwin saw extinction purely as a matter of a species losing its battle of survival of the most fit. He would not have conceded any deus ex machina role played by obliging comets. Darwin was probably wrong about this.
When I read Raup’s Extinction book, I was drawn to its center-piece theory because of parallels to the development of the theory of continental drift. My own book, The Mountain Mystery, tells the story of plate tectonics’ reluctant acceptance. Tectonics theory made the journey from pariah to popular about thirty years before the idea of mass extinction by falling rocks became a legitimate theory. With the tectonics hypothesis, scientists began with hesitant appeals to their colleagues – Harry Hess, a major advocate of seafloor spreading, first presented his idea as “geo-poetry” and offered his most famous paper (“History of Oceans“) in a rather tentative manner. (My book has an entire chapter called “Poetry in Motion” describing Hess’s creeping disclosure.) David Raup describes one of his first attempts to publicly promote the impact theory, in 1988:
“I presented a paper suggesting the universality of extinction by impact. The idea was apparently well received but largely because I labeled it a “thought experiment” and did not claim actually to believe it.” – David Raup, Extinction.
When Raup’s book was published, the Chicxulub Crater had just been discovered by petroleum geologists working in the Gulf of Mexico. Raup writes, “As I write this chapter in June of 1990, the scientific community is digesting two recent reports focusing on the Caribbean. One investigates a possible crater underlying the Yucatan, and the other describes rocks in Haiti that suggest deposition following a huge impact.” Raup continues:
“Perhaps within the next few months, it will be difficult to find anyone who ever doubted the impact-extinction link. That happened in the 1960s with the acceptance of plate tectonics and continental drift.” – David Raup, Extinction.