The shifting sands of the Gran Desierto de Altar, a vast dune sea east of where the Colorado River once met the Gulf of California, offer a living metaphor for geological processes that shaped landscapes over eons. The slow, relentless movement of these dunes, with sand climbing one side and cascading down the other, mirrors the depositional forces that created ancient rock formations like the Coconino sandstone in the Grand Canyon. The sweeping diagonal lines etched into these rocks, visible to this day, record wind directions from an astonishing 280 million years ago, embodying the geological principle that the present holds the key to understanding the past. However, Earth’s history is not solely a narrative of gradual change; it is also punctuated by cataclysmic events, most notably the "Big Five" mass extinctions that fundamentally altered the course of life and planetary evolution. By delving into these profound transformations and incremental shifts recorded in the rock strata, we gain invaluable insights that can inform our present decisions and illuminate potential future trajectories. Grasping how vast geological formations like the Coconino, which spans thousands of square miles, could have accumulated over millions of years requires a fundamental shift in our perception of time, an immersion into what geologists term "deep time." This profound engagement with Earth’s ancient past can foster a deeper understanding of the long-term consequences of our actions today.

John McPhee, a celebrated writer for The New Yorker, was instrumental in popularizing the concept of "deep time" with his 1981 book, Basin and Range. This seminal work, now best experienced through the lightly updated version within his 1999 Pulitzer Prize-winning anthology, Annals of the Former World, serves as an accessible introduction to Earth’s multi-billion-year history. While initially published during the Reagan administration and revised in the Clinton era, McPhee’s narrative, grounded in the observations of geologists, retains its remarkable relevance. McPhee sought to capture the most compelling narratives within North America’s ancient geological saga by immersing himself in the landscapes and events that geologists decipher from rock formations. His method involved accompanying geologists on their cross-continental journeys, most notably along Interstate 80 from New Jersey to Nevada.

In the arid expanses of Utah and Nevada, McPhee explores the dramatic geological phenomenon of basin and range topography – the characteristic alternation of long, parallel mountain chains, or ranges, separated by equally extensive valleys, known as basins. Geologists explain this striking pattern through the fundamental processes of faulting, which creates the depressions of the basins, followed by the infill of sediments. This dynamic geological story, though more recent than the age of dinosaurs, still unfolds over millions of years. McPhee highlights how the North American continent is actively being "pulled to pieces" in the vast region between the Rocky Mountains and the Sierra Nevada. This is not an unprecedented event; a similar continental rifting occurred approximately 200 million years ago when the supercontinent Pangaea began to break apart, paving the way for the formation of the Atlantic Ocean. This geological perspective prompts reflection on the continent’s future, even raising the speculative question of whether Nevadans might one day "wave to Californians across a new sea."

McPhee’s narrative is rich with digressions, offering glimpses into human history intertwined with geological landscapes. In one such detour, a geologist guides him to an abandoned silver mine in Nevada. They traverse a precarious road overlooking a valley that McPhee notes held profound cultural significance for the Paiute people, akin to the Black Hills for the Sioux. Here, he learns about the legacy of 19th-century mining, where the most accessible and richest silver veins were extracted, potentially leaving behind millions of dollars worth of ore as discarded waste.

McPhee also deftly navigates the immense scale of geologic time, contrasting it with human perception. "People think in five generations – two ahead, two behind – with heavy concentration on the one in the middle," he observes. Geologists, in their discussions with McPhee, grapple with the challenge of measuring deep time, an expanse so vast that it defies ordinary human comprehension. McPhee’s book functions as an essential primer, an invitation to understand how geologists can "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."

Science journalist Laura Poppick, in her July 2025 book, Strata: Stories from Deep Time, echoes McPhee’s meticulous attention to detail, yet offers a distinct approach to exploring Earth’s ancient history. Poppick’s work is a tapestry of meditative prose, thematically organized into chronological explorations of fundamental elements: air, ice, mud, and heat. She investigates rocks dating back 2 to 3 billion years, which hold crucial clues about the origin and evolution of oxygen in our atmosphere. Poppick travels to Minnesota to examine iron-rich rocks from a period of profound global anoxia, a time when Earth’s atmosphere contained virtually no free oxygen. This existence of such iron deposits indicates a lengthy preceding period – nearly half of Earth’s history – before oxygen became a significant component of the atmosphere. The ancient atmosphere, so alien to our own, laid the groundwork for the emergence of life as we know it, and consequently, the development of materials like iron that are fundamental to our modern technological world, from "steel cars and kitchen appliances and medical devices and airplanes."

Approximately 540 million years ago, a pivotal moment in evolutionary history, the Cambrian explosion, witnessed the rapid diversification of life, giving rise to nearly every major animal group present on Earth today. Paleontologists meticulously reconstruct this evolutionary trajectory and the impact of mass extinction events by studying the fossilized records preserved within rock layers. Poppick delves into two of the planet’s "Big Five" mass extinctions: one occurring around 250 million years ago, and another roughly 50 million years later. Unlike the more widely known dinosaur-killing asteroid impact, these profound die-offs appear to have been triggered by immense volcanic eruptions in geologically unfortunate locales. Poppick explains, "The magma that welled up from the mantle sat directly beneath massive reservoirs of oil, gas and coal. 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 historical account of catastrophic events serves as a powerful, and perhaps cautionary, parallel for understanding our planet’s potential future under current environmental pressures, offering potential pathways toward mitigation.

Climate models suggest that the Mesozoic Era, the age when dinosaurs dominated, experienced temperatures between 14 to 25 degrees Celsius (25 to 45 degrees Fahrenheit) warmer than present-day averages. Poppick explores how life adapted to these extreme "hothouse" conditions, accompanying scientists on expeditions to a significant fossil site in Wyoming in search of evidence of the largest land animals ever to exist – the long-necked sauropods such as Diplodocus, Brontosaurus, and Apatosaurus.

More than just the skeletal remains, these scientists are focused on understanding the ancient ecosystems that supported these colossal herbivores and how these environments, along with their inhabitants, evolved over time. Their research centers on the Morrison Formation, a vast sequence of sedimentary rock layers stretching from New Mexico to Montana, which has yielded more dinosaur fossils than any other rock formation on the continent. The deposition of these rocks spanned approximately 9 million years, thus preserving a detailed record of dinosaurian history. Poppick aptly notes the immense timescale involved: "By way of comparison, just twelve million years or so of evolution produced humans, gorillas and chimps from the same common ancestor." By studying the intricate layers of the Morrison Formation, scientists endeavor to unravel the environmental conditions that allowed sauropods and other dinosaurs to thrive in the Jurassic warmth. Poppick observes that as our understanding of this ancient period deepens, so too does our appreciation for Earth’s resilience and capacity to sustain life under varying climatic conditions.

To truly immerse oneself in the world of the Morrison Formation, the February 2025 publication, When the Earth Was Green, by science writer and paleontologist Riley Black, offers a captivating experience. Black masterfully blends scientific data with artistic prose, enabling readers to vividly imagine ancient ecosystems. Each chapter is presented as a compelling vignette, accompanied by an appendix that details the current scientific consensus, speculative hypotheses, and the author’s own inspired interpretations.

In Black’s reimagining of Utah 150 million years ago, readers are transported beyond the fossil sites in Wyoming, embarking on a journey through time. Black paints a scene of an Apatosaurus feeding in a lush woodland, its diet consisting of vast carpets of horsetail and an ancient ancestor of the modern ginkgo tree. The dinosaur’s long, muscular neck allows it to browse both the high canopy and the forest floor, while its immense size offers a significant defense against predators. Black emphasizes that the very existence of such gargantuan herbivores is a testament to the unique and abundant nature of their prehistoric habitat, characterized by towering conifers rising from a dense undergrowth of ferns and cycads. This rich botanical landscape was essential for the sauropods to attain their colossal size, illustrating a profound "evolutionary dance between herbivores and plants." In her previous work, The Last Days of the Dinosaurs, Black meticulously chronicled the fifth of the Big Five extinction events with a focus on the granular progression of seconds, minutes, hours, days, and years. In When the Earth Was Green, her focus shifts from catastrophe to the intricate interplay of life, depicting the daily existence of creatures and plants co-evolving and leaving behind the subtle imprints of their intertwined stories preserved within the rocks.

McPhee’s writing style is akin to embarking on a road trip in the 1970s with a witty journalist and an eccentric geologist uncle who exclaims "Shazam!" at the sight of remarkable rock formations; while not every nuance may be immediately grasped, the journey is undeniably exhilarating. Poppick, in contrast, invites readers to participate in scientific discovery through field trips, research collaborations, and laboratory visits, revealing the engaging process of scientific inquiry. Black, meanwhile, transports readers to nearly dreamlike landscapes, employing vivid descriptions to bring long-vanished worlds to life, using her imagination and scientific knowledge to evoke the experience of deep time. As Poppick wisely observes, "Our planet seems to be telling us to take a look back." Each of these books offers a unique and invaluable guide through the immensity of deep time, prompting a profound contemplation of our own place within the grand, unfolding narrative of Earth.