This piece is part of a special project on deep time examining what the Western U.S. was like thousands, millions and even billions of years ago, and how that history is still visible and consequential today. Read more stories from the series.
Just east of where the Colorado River used to trickle into the Gulf of California, the dunes of the Gran Desierto de Altar are slowly migrating. Sand blows up their gentle sides; at the top, grains tumble down, and the dunes creep stealthily along. Observing these incremental processes IRL can illuminate the story of rock outcroppings like the Grand Canyon’s Coconino sandstone, which features sweeping diagonal lines signaling the direction wind traveled 280 million years ago. As geologists say, the present is the key to the past.
But the rock record also documents far-reaching and sometimes global catastrophes, like the “Big Five” mass extinctions that irrevocably changed our planet, shaping everything that came after.
As it turns out, the past — with its mix of both incremental and catastrophic happenings — can inform our present, and even our future. But to grasp what the rocks have to say requires grappling with how a formation like the Coconino, which spans thousands of square miles, could have been deposited over millions of years. Learning how to think about what happened so long ago — venturing into “deep time” — can help us better understand the repercussions of our choices today. Here are three books that take us into the geologic past.
The term “deep time” was popularized by longtime New Yorker writer John McPhee in his first foray into Earth science, 1981’s Basin and Range. I recommend reading the lightly updated version in his 1999 Pulitzer Prize-winning five-books-in-one anthology, Annals of the Former World. The original Basin and Range was published when Reagan was president and revised in the Clinton era; since then, some numbers have been refined, and some concepts are no longer new. Yet more often than not, the stories McPhee tells retain their relevance.
McPhee wanted to write about what he thought were the most interesting pieces of North America’s billions-year-old history “by describing events and landscapes that geologists see written in rocks.” He did so by tagging along with geologists as they crossed the continent on Interstate 80 from New Jersey to Nevada, where the book ends.
In Utah and Nevada, McPhee explores the emergence of long lines of mountains, called ranges, separated by similarly long valleys, or basins. Range, basin, range, basin, goes the pattern. “Faulting produced this basin,” a geologist tells McPhee. “Sediments filled it in.” That’s the simple version, anyway. It’s a story younger than dinosaurs, yet still millions of years old.
McPhee explores how the continent is “being literally pulled to pieces” between the Rocky Mountains and the Sierra Nevada. Not the first time, either: this rending of Earth, one of McPhee’s tour guides explained, happened 200 hundred million years ago when the supercontinent Pangea began to rupture, eventually letting the Atlantic Ocean in. In the future, will Nevadans wave to Californians across a new sea?
Strata: Stories from Deep Time
Laura Poppick
288 pages, hardcover: $29.99
W.W. Norton & Co., 2025.
McPhee takes detours aplenty, as when his geologist companion takes him to an abandoned silver mine in Nevada. They follow a treacherous road overlooking a valley that McPhee describes as being as special to the Paiutes as the Black Hills are to the Sioux. McPhee learns how 19th century miners took all the best silver but left potentially millions of dollars’ worth of ore in the trash.
McPhee also veers into the vastness of geologic time. “People think in five generations — two ahead, two behind — with heavy concentration on the one in the middle,” he writes. Geologists muse to McPhee about how we can measure deep time without truly comprehending the passage of millions of years.
Consider McPhee’s book a primer, an introduction to rocks, a way to understand how geologists “inhabit scenes that no one ever saw … archipelagos of aching beauty rising in volcanic violence to settle down quietly and then forever disappear — almost disappear.”
Annals of the Former World
John McPhee
720 pages, softcover: $30
Farrar, Straus and Giroux, 2000
Science journalist Laura Poppick explores some of the same history, writing with similar attention to detail as McPhee in her book Strata: Stories from Deep Time, published in July 2025. Yet Poppick’s book, threaded with meditative prose, is entirely different: It is a story of deep time divided into chronological themes — air, ice, mud and heat.
Rocks between 2 billion and 3 billion years old contain clues regarding when and how oxygen first entered our atmosphere. Poppick goes to Minnesota to see rocks abundant in iron from that time of worldwide anoxia. For such iron deposits to exist, there must have been a time — about half of Earth’s existence — before the ether held oxygen. The air billions of years ago set the stage for our existence and the way we live today, facilitating the formation of the iron we use for our “steel cars and kitchen appliances and medical devices and airplanes,” she writes.
When the Earth was Green
Riley Black
304 pages, hardcover: $29.99
St. Martin’s Press, 2025.
Around 540 million years ago, the Cambrian explosion of life occurred when almost every animal group existing today first came into being. Paleontologists track this evolution and how much was obliterated in mass extinction events by studying the fossils found in rocks.
Poppick details two of the Big Five major mass extinctions — one that happened
250 million years ago, and the next, about 50 million years later. Unlike the later dino-killing asteroid impact, both these die-offs seem to have been caused by immense volcanic eruptions in unfortunate locations. “The magma that welled up from the mantle sat directly beneath massive reservoirs of oil, gas and coal,” Poppick explains. “As that magma rose to Earth’s surface, it burned and combusted those fossil fuels, releasing not only carbon dioxide but also toxic butanes and benzenes and ozone-depleting gases.” This story of past catastrophes is a familiar one that may help us understand our sweltering future, “and how we might find a way out.”
Modeling suggests that the seemingly endless summer in which dinosaurs ruled was hotter than it is today by between 14 and 25 degrees Celsius — between 25 and 45 degrees Fahrenheit warmer than we’re used to. How did animals survive this hothouse? Poppick accompanied scientists to a secret site in Wyoming in search of remnants of the largest land animals that ever lived — long-tailed, long-necked sauropods like Diplodocus, Brontosaurus and Apatosaurus.
“People think in five generations — two ahead, two behind — with heavy concentration on the one in the middle.”
More than the bones themselves, these scientists are interested in the environment that nurtured these gigantic herbivores, and how it, and its denizens, changed over time. They’ve been studying ecosystems in the Morrison Formation — layers of sedimentary rock from New Mexico to Montana and beyond that have “spilled out more dinosaur bones than any other rock formation on the continent.” It took about 9 million years for these rocks to be deposited, and so they contain 9 million years of dinosaurian history. “By way of comparison, just twelve million years or so of evolution produced humans, gorillas and chimps from the same common ancestor,” Poppick notes.
Scientists studying the Morrison’s layers puzzle out how sauropods and other dinosaurs flourished in that Jurassic warmth. “As we inch closer to a clearer picture (of that time), we deepen the intimacy with which we know Earth and its capacity to withstand heat,” Poppick writes.
But to truly inhabit the Morrison, we should turn to a book published in February 2025. In When the Earth Was Green, science writer and paleontologist Riley Black infuses data with artistry to help us experience what ancient ecosystems might have felt like. Each chapter is written as a vignette accompanied by an appendix “detailing what we think we know, what we might guess at, and what simply struck (the writer’s) fancy.”
When Black imagines Utah 150 million years ago, we don’t poke at the Jurassic leftovers that Poppick visited in Wyoming. Instead, we go time-traveling.
Black follows a hungry Apatosaurus feeding in a vast woodland, consuming carpets of horsetail and an ancestor of today’s famously stinky ginkgo tree. The animal’s long muscular neck lets her reach high into the canopy and down to the ground, while her great size protects her from being too bothered by predators.
“The fact that she exists at all is a testament to the strange nature of her habitat,” with its towering conifers rising from a sea of ferns and cycads. Without this salad bar, sauropods could not have grown so big. This, Black tells us, “is an evolutionary dance between herbivores and plants.”
Black’s previous book, The Last Days of the Dinosaurs, explored the fifth of the Big Five extinctions in heart-wrenching detail by seconds, minutes, hours, days and years. In When the Earth Was Green, she focuses less on catastrophe and more on a day in the life of the creatures and plants that nudge each other as they co-evolve, leaving remnants of their intertwining stories sheltered in rocks.
“By way of comparison, just twelve million years or so of evolution produced humans, gorillas and chimps from the same common ancestor.”
With McPhee, you’re on a road trip in the 1970s with a journalist and your weird geologist uncle who yells stuff like “Shazam!” when he sees cool rocks. You may not get all their jokes, but the ride is wild. With Poppick, you step through deep time by joining field trips, participating in research and visiting labs. This is how science happens — and it’s surprisingly fun. Meanwhile, Black thrusts readers into almost dreamlike landscapes with her vivid descriptions of long-vanished worlds. She uses her imagination and knowledge to help you experience deep time.
“Our planet seems to be telling us to take a look back,” Poppick writes. Each of these books help us do that, guiding us through deep time and prodding us to consider our place within it.
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This article appeared in the January 2026 print edition of the magazine with the headline “What’s past is prologue.”
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