Supercontinent: Ten Billion Years in the Life of Our Planet
Harvard University Press, 2007
304 pp., $29.95
by Stephen O. Moshier
The Upper Crust
Editor's Note: This article first appeared in the July/August 2008 issue of Books & Culture. Its subject is a book that traces "the long and convoluted history of continental drift." Along the way, reviewer Stephen Moshier has some illuminating things to say about science, religion, creationism, and the misunderstandings that often bedevil discussions of these intertwined subjects.
Continental drift first captured my imagination in elementary school. The front page of a particular Weekly Reader featured a drawing of the earth floating in space. But this globe showed the continents all bunched together in a single landmass scientists called Pangaea. Of course! Why hadn't I noticed that the Atlantic coastlines of the Americas, Europe, and Africa fit together so perfectly, like pieces of a planetary jigsaw puzzle? The article announced that finally, after many years of investigation, scientists had enough evidence to show that, indeed, continents drift. We were witnessing a major revolution in science, what philosophers call a paradigm shift. For in the middle 1960s, the idea of continental drift was at the tipping point of acceptance by the scientific community.
In Supercontinent: Ten Billion Years in the Life of Our Planet, author Ted Nield writes that the long and convoluted history of continental drift is actually three stories. The first story is about the scientific work that led to the modern geological paradigm of plate tectonics. Nield is keen to make this a story about people, including some of the most colorful scientists and explorers of the 20th century. The second thread is the story of earth history, with its changing geography, climate, and ecology. The third thread might be the most interesting to many readers, as Nield explores how Pangaea belongs to the company of "lost continents" that have captured imaginations, even fueled religious convictions, from Aristotle's Atlantis to the new age Mu. Nield weaves a thorough history of plate tectonics for popular audiences, drawing from historians of science (including Naomi Oreskes) and his personal relationships with contemporary workers at the cutting edge of research and discovery. As editor of Geoscientist, the magazine for Fellows of the Geological Society of London, Nield knows the material intimately and communicates it in a compelling manner.
The theory of plate tectonics is one of the major scientific achievements of the 20th century. Most geology textbooks tell the story as if it involved only two or three scientists, but Nield celebrates the wider cast of characters. Every student of geology learns about Alfred Wegener (1880-1930), the German atmospheric scientist who showed that rocks, fossils, and mountain belts match exactly where the continents can be fitted together. As a specialist on climates, Wegener was particularly interested in the distribution of glacial deposits from the Permian geologic period found on all the southern continents. He argued that if the continents at that time were in their present positions, an ice sheet would have implausibly extended from the South Pole to the equator, covering wide expanses of open ocean. The first edition of Wegener's Origin of Continents and Oceans was published in 1915, but his ideas were not adopted in his lifetime. Wegener perished in Greenland attempting to measure the movement of that particular icy landmass from Western Europe.
Nield resurrects the memory of forgotten and courageous 19th-century European geologists who mapped rocks in India, South Africa, and Australia, work that contributed to Wegener's synthesis. Preceding Pangaea, continents with names like Lemuria and Gonwanaland were proposed to explain distributions of organisms on southern continents that would seem to have required connections by land (so-called land bridges). But scientists eventually abandoned those hypothetical terrains as new evidence emerged.
While geologists were mapping the continents and comparing notes, geophysicists were learning about heat in the earth and developing models for how mountains rise and fall, leading to a comprehensive understanding of how the earth works. The synthesis of continental and marine geology with the geophysics of the inner earth came after World War II. Maps of the seafloor revealed the submarine boundaries of lithospheric plates that merged with mountain belts and fault zones on the continents. It turned out that continents are like lunch trays on a conveyor belt. Magnetic properties of the ocean crust revealed patterns of seafloor spreading away from mid-ocean ridges (where the conveyor belt begins). Mountain ranges, explosive volcanoes, and deep earthquakes mark the locations of plate convergence, even creating deep ocean trenches where ocean crust is pushed back into the earth (where the conveyor belt ends). You get Pangaea at the cafeteria when trays approaching the dishwasher collide into a mangled mess.