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The disappearance of nonavian dinosaurs is only a small part of a greater class of extinctions known as “mass extinctions.” Mass extinctions are global events characterized by unusually high rates of extinction. The five episodes of mass extinctions in Earth history are the Permo-Triassic extinction, the Late Ordovician extinction, the Late Devonian extinction, the Triassic-Jurassic extinction, and the Cretaceous-Tertiary (K/T) extinction. This chapter focuses on patterns of geologic and biotic changes that occurred during the Cretaceous-Tertiary (K/T) extinction. It also highlights the similarities and differences in interpretations of geologic and fossil records. It concludes with two scenarios explaining the differing views about dinosaur extinction.

This chapter examines the social and political meaning of dinosaur paleontology in popular culture. It considers three case studies: the paleobiology of the large theropod T. rex, the discovery of dinosaur maternity, nests, eggs, and embryos, and the dinosaur extinction. The analysis reveals that important discoveries about the biology, behavior, and extinction of dinosaurs were influenced not just by empirical developments, but also by the social climate of the times in which they were produced.

Nuclear war analysts often compared nuclear detonations to volcanic eruptions. The connection between volcanic eruptions and climatic changes, suggested long ago by Benjamin Franklin and others, received serious interest from researchers only in the early twentieth century. Today, however, a direct comparison between volcanic eruptions and nuclear war is deemed inappropriate owing to the different absorption properties of sulfuric acid and silica dust than dark smoke. Furthermore, the distributions of particle sizes are different, and warfare would give rise to fine particles from a variety of sources rather than a single location. This chapter examines scientific disciplines with less obvious connections to nuclear war, including volcanic eruptions, ozone depletion, planetary studies, dinosaur extinction, and the asteroid impact hypothesis.

The federal government was hopelessly in a dilemma about nuclear winter, concerned that it might force a reconsideration of its national policy. The military was less apprehensive, recognizing quite early the significance of these studies and showing a willingness to obtain honest advice. In 1982, the National Academy of Sciences was conducting a study to evaluate the link between dinosaur extinction and dust, rather than nuclear winter. Meanwhile, the Department of the Navy, always technologically oriented, made its own efforts to keep informed about nuclear winter. In 1983, Carl Sagan advocated “minimal deterrence” and encouraged a “build-down” to the approximate nuclear winter threshold level of 100 MT by the end of the century. He also presented a layman’s summary of the physical and biological consequences of nuclear war as recently determined by his TTAPS team (comprised of Richard Turco, Owen Brian Toon, Thomas Ackerman, James Pollack, and himself) and their colleagues.

When the Alvarez team announced to the world that the K/T boundary clay contained a excess of iridium they suggested that it could only be explained if a comet or asteroid had slammed into the earth 65 million years ago. The iridium was deposited when a cloud of debris created by the vaporization of the object upon impact girdled the earth and fell back to form the so-called fireball layer. Most earth scientists were skeptical when they first heard about this. If an object 10 kilometers across had collided with enough force to trigger a global environmental catastrophe that precipitated the extinction of more than half of the species alive at the time, where was the crater? It didn’t take crater experts long to figure that the scar left by such an impact should be huge hole in the ground about 180 kilometers across and a tenth as deep. If it existed, it shouldn’t be hard to find, unless it was under the ocean somewhere, or covered in vast amounts of sediment. It turns out that when the search for the crater began there were several people, perhaps dozens, who already knew where it was. However, they either didn’t know that the search was on, or weren’t allowed to reveal what they knew. The saga of the discovery of the K/T impact crater beneath the north coast of the Yucatan Peninsula of Mexico began many decades before the discovery of iridium in the K/T boundary layer. The saga goes all the way back to 1947 when a gravity survey was started in the Yucatan by the Mexican national oil company, PEMEX. Surface gravity measurements allow geophysicists to detect the structure of rock formations deep beneath the earth’s surface. The study of gravity maps of a region then helps the scientists to figure out where oil might be found; at least that is the goal. The Yucatan survey turned up some intriguing data, including hints of a circular feature some 1,000 meters deep. In the early 1950s test wells were drilled, but no oil was found.