Book Review: How the Mountains Grew
If you’ve ever looked at a globe and noted how, with a little bit of counterclockwise rotation, eastern South America could snug up against western Africa with the Softclick precision of a couple of Ravensburger puzzle pieces, the notion that the continents move seems pretty obvious. Geologists had noticed this as well from very early in the science’s history, and as more of the Earth was explored, they consistently found rock formations and fossils of the same age and with the same patterns of layering that were literally oceans apart. How had these rocks, which clearly originated at the same place and time, been separated? In 1912 Alfred Wegener put forward the theory of continental drift, but he had no sufficient explanation for how or why the continents drifted. By the late 1960s, however, the evidence Wegener lacked had been found in such a preponderance and from such a diversity of fields (contributions came from seismology, paleoclimatology, paleomagnetism, oceanographic exploration and others) that geoscientists were able to put forth a coherent theory to explain the mechanisms behind the movements, a theory known as plate tectonics.
Plate tectonics is the main character in John Dvorak’s How the Mountains Grew: A New Geological History of North America. Dvorak starts his history, with apologies to Julie Andrews, at the very beginning—i.e., the Hadean Eon, during which Earth formed and gained a moon via a rather nasty impact with a large body called Theia. The Hadean ended “when the rock record begins on the Earth, when the earliest known crustal rock, the 4.030-billion-year-old Acasta Gneiss, formed” (19). The Acasta Gneiss is found in Canada, while its somewhat younger cousin, the Morton Gneiss (3.850 billion years old), may be found in a few outcrops near Morton, Minnesota. The Morton Gneiss is the oldest rock yet found in the United States, but when it first formed deep within the earth, it was a dull gray granite. The pink, gray and black swirls that make it a coveted building material today were generated when a tectonic plate bearing its gray granite collided with a tectonic plate bearing pink granite about 2.5 billion years ago. The heat and pressure from the collision caused the two granites to fold and twist together, and a later event produced more color and texture and led to the Morton Gneiss’s current form.
You can see photos of the Morton Gneiss in the book’s section of color plates. I wish all of the illustrations were in color; it’s hard to see layers and texture in some of the black and white photos throughout the text. But this is a small gripe, easily outweighed by the book’s greatest strength: as the chapters march forward from the Archean to the Anthropocene, Dvorak grounds each interval in a place where one or more formations tell the story of that time, linking contemporary geography to geological forces both ancient and ongoing. And unlike greedy rockhounds (like me) who’d sooner give you their Social Security number and bank password than tell you where they found this trilobite or that geode, Dvorak cites/sites his sources. Wanna see Cameron’s Line, a suture fault that formed during the Taconic Orogeny in the Ordovician? Go to “the Bronx at Boro Hall Park (also known as Tremont Park) where a rocky outcrop of the Manhattan Formation lies just outside the right-field fence of a baseball field while an outcrop of the Hartland Formation is found near the left-field fence” (104). Wanna see an erratic—i.e., “a boulder that is found in isolation and differs from the types of rocks that are native to the surrounding area” (313) and was often dropped in its current location by a glacier? Visit “the Wedgwood Rock in the Wedgwood neighborhood of Seattle [which] has a mineral content that matches the exposure of rock at Mount Erie on Fidalgo Island in Washington, a distance of about fifty miles from where it lies today” (315). I love that Dvorak frequently gives me enough detail that I could follow in his footsteps and see for myself what he writes about.
I also appreciate Dvorak as a writer. He does not dumb his subject down for the masses. The book is hardly a geophysics text, but the prose in his deep exploration of the fault systems that crackle and pop across the western U.S. reflects the complexity of the region’s very active geology. I had to reread a few of those passages to make sure I grasped the various types of faults and the plate tectonics that explains how and why these chunks of Earth move the way they do (though admittedly if you gave me a quiz on this now that I’ve closed to covers, I would flunk it). But at his heart, Dvorak is a storyteller, and he wants his readers to feel the same drama and awe of the land and the geological tale of its past and present that he does. He also wants us to understand the impact our species has had—and is having—on the planet. When we invented agriculture, we likely stabilized the world climate, preventing another ice age. But when we started using fossil fuels, we began to upend that stability, and the results are becoming clearer and clearer. Dvorak deploys hard numbers to illustrate the increase in temperature and the concentration of carbon dioxide in the earth’s atmosphere, which has risen from 280 parts per million in the age of George Washington and Thomas Jefferson to 416 parts per million today. If emissions continue at their current rate, we will hit 900 parts per million by the end of the century. If that number generates a shrug, maybe the visualizations provided in the graphs on page 350 will provide more of a jolt. My eyes definitely got wider. I’m sure some folks would prefer it if Dvorak just stuck to the past, but his point isn’t controversy; it’s observation of how the forces that have shaped our world throughout its history continue to operate in the present. The first fifteen chapters of How the Mountains Grew bring the past alive in the present and provide the context we need to understand that we are not just witnesses to but also participants in the grand, sweeping processes that shape and reshape the Earth.
Learn more about John Dvorak and his work.