I took a step — a long step — a million years step. Then I stopped, turned and faced north. Perched on the jagged edge of my life, I looked down deep into the shadowed layers of lost worlds — terrible deaths, fractured continents, vanished seas, mass extinctions.
Taking a breath, I took another step — a long step — another million years.
Curiously, I felt better — my troubles for the moment shrunk to no more than a ledge of Tapeats Sandstone in the wall of the Grand Canyon opposite. A layer of fossilized beach sand laid down 570 million years ago, the Tapeats Sandstone lies atop a mystery of missing stone — dubbed the “Great Unconformity.”
I studied that light, crumbling layer of sandstone in the canyon wall just across the way, knowing that all the great, riotous thrust of life that took us from pond scum to troubled writers has taken place since the lapping waves of a vanished sea left that layer of crumbling gray stone on a barren beach.
Perched on the wind-tormented branch of a twisted juniper nearby, a glossy black raven croaked at me.
“Nevermore,” he gurgled in my mind’s ear.
“You raise a good point,” I said to the raven and the wind that rose up out of the canyon’s 1.8-billion-year gash of time. I let loose a breath, a sigh, a puff of steam — frail and fleeting as life in the shadow of so much time. It should have depressed me, to stand so mite-like on the edge of such immensity. All I had dreamed or hoped or failed to do would not amount to a swirl of dust on this crumbling edge. I ought to have felt insignificant. Instead, I felt obscurely better.
So I took another step. A long step — a million years.
They had not built the Trail Through Time along the edge of the Grand Canyon between the El Tovar and Yaqui Point the last time I lingered on this edge. Now, it offers the most exciting crash course in geology I’ve ever encountered, although I’ve sought after rocks and unconformities all my life — and have even written geology books for confused people.
The 1.2-mile-long trail presents sliced and polished rocks representing almost all of the 24 major rock layers laid bare in the canyon wall from the 240-million-year-old limestone, siltstone, gypsum and chert layers of the Kaibab Formation to the 1.8-billion-year-old Vishnu Schist in the canyon bottom, among the oldest exposed rock’s on the planet’s surface.
Each step along the 1.2-mile path represents a million years, starting in the present and ending up at the 1.8-billion-year-old start of everything.
The Grand Canyon represents the most vividly revealed slice of Earth’s history anywhere on the planet. That makes the canyon one of the few places a person can grasp both the astonishing violence and the tormented timescale of the planet that sustains us all. This unique cross-section of time comes as a result of the relatively level uplift of the Colorado Plateau in the past 5 million to 8 million years. In most places, such a vast uplift would jumble the buried rock layers. But much of the 130,000 square miles of the Colorado Plateau rose at the rate your fingernails grow without deforming the miles-deep layers of sandstones, limestones and shales laid down on the bottoms of long-vanished seas and deserts.
As the Colorado Plateau rose, the northern edge crumpled into the Rocky Mountains. The southern edge dropped away along a 200-mile-long chain of 1,500-foot cliffs — which north of Payson forms the Mogollon Rim. Oak Creek cut back into that rising edge of the plateau to uncover the striking red rock formations of Sedona.
The Colorado River did the same thing, but on a grand scale. Many geologists believe the Colorado River originally ran north into a vast, interior sea. But as the Colorado Plateau rose, another river that ran south cut backward until it captured the north-flowing ancestral Colorado River, reversing the flow so that it now ran south into the Gulf of California.
This capture some 6 million years ago began the process of carving out the Grand Canyon. As the plateau rose, the flood-prone Colorado River cut down through it, like pressing a log up against a chain saw. Meanwhile, the steep tributaries widened the canyon by carrying those soft layers of sedimentary rock down to the main stem of the Colorado.
That process started at about the time the genetic evidence suggests humans, chimps and gorillas last shared a common ancestor and continues to this day.
As a result of this vast uplift, the relatively young Colorado River has revealed in the walls of the Grand Canyon the long buried history of the Earth going back nearly halfway to its creation. That encompassed the entire period in which life progressed from single celled organisms in the ocean to its present, dazzling complexity.
The meander down that Trail Through Time reveals much of that history, preserved in the rock layers and the fossils they contain. Of course, erosion has already removed more than 200 million years of that history, so that the youngest rocks on the rim of the canyon are older than the dinosaurs.
A few dominant layers stand out.
Near the top, the fossilized desert sand dunes of the light Coconino Sandstone bear witness to a vast desert that covered the Southwest some 260 million years ago. At that time, what would become North America was part of a “supercontinent” that gathered almost all the dry land on the planet into a single mass.
In the middle of the canyon, lies the great, blood-red wall of Redwall Limestone, formed on the bottom of a shallow sea between 300 million and 400 million years ago. Today, the fused layers of microscopic skeletons of ancient sea creatures forms a sheer 500-foot-tall band of cliffs that pose the greatest single barrier to reaching the canyon bottom from the rim. All of the trails to the bottom must pass through fault lines in the Redwall Limestone, stained red by iron oxides leaching out of the layers above.
Farther down, the easily eroded Bright Angel Shale forms the shelf above the 1,800-foot-deep inner gorge. Shales form on shallow sea bottoms, compared to the deeper marine environments that create limestones. Most of the trails in the canyon run along its wide shelf. Formed 530 million years ago, the Bright Angel Shale represents the era when trilobites ruled the world.
Just below the Bright Angel Shale lies the Great Unconformity, where erosion in the inconceivably distant past removed 1.2 billion years worth of rock. This records another period of uplift, when erosion carried off layers of rock many times higher than Mt. Everest.
Below that unconformity, the story continues — down through a dozen more layers in the inner gorge, each one mounted alongside the trail and polished smooth. The Grand Canyon Supergroup spans the period between 570 million and 1.2 billion years ago, again recording the meanderings of the continents and the ebb and flow of oceans, as the planet breathes in, breathes out.
After another, smaller unconformity, the river finally reveals the inconceivably ancient Vishnu Schist and Zoraster Granite. The schists started as sandstone, limestone and shale, before they were buried, reheated and fused into this dense, primordial rock. The Zoraster Granite ooze up from the molten depths of the Earth, forming veins revealed finally by the relentlessly downcutting river.
I could not see the metamorphosed Vishnu Schist from my perch atop the rim, but I have seen it on raft trips in the dark heart of the canyon where it has been fluted and carved and sandblasted by eons of floods.
Finally I stood stock still, my breath coming still in moist, warm, puffs as the planet spun so that the dust of the atmosphere gave the sun’s long light a warm red glow, reflected off the ancient worlds across the way.
My raven friend — or one of his kin — flew past with an audible whoosh of his wings, then banked to consider the possibilities. He croaked, that guttural warble that only ravens dare.
Odds are, he noted my proximity to the edge and so paused to ponder my potential as carrion.
But I prefer to think that he felt our shared pulse of life and caught the updraft of my yearning.
In either case, he settled on the branch of a weirdly stunted ponderosa pine nearby and we shared the sunset.
The shadows rose up out of the canyon, swallowing continents and oceans.
I kept my gaze on the glow of the Redwall Limestone until the shadow took it, then shifted to the luminous yellow of the Coconino Sandstone.
For I came to the canyon full of woe holding my life in my fingernails, my heart in the shadows. But now my troubles seemed fleeting, the world full of marvels, my life aglow like that desert turned to sandstone in the last light of day.
My breath came in a puff, transparent but warm in the still, cold air.
“Nevermore,” quoth the raven, “nevermore.”