Rock of ages: Oman's open-air museum

Imagine you woke up one morning with an unusual ambition: to see the Earth's mantle with your own eyes — that mysterious, slowly churning layer of green-black rock that makes up most of our planet's volume, yet which no human being has ever visited. You have two options. Option one: start digging. You'll need to burrow through 35 to 70 kilometres of solid crust — a sobering task, considering the deepest hole humanity has ever managed, Russia's Kola Superdeep Borehole, gave up at 12.2 kilometres, and the deepest any human has physically descended is barely four kilometres, in the gold mines of South Africa, where the rock walls are hot enough to fry an egg. Option two: fill up the car, pack some karak chai in a flask, and drive to the Hajar Mountains of northern Oman. There, the mantle is simply lying about in the open — sunbathing, as it were — waiting for you to park beside it and place your palm on the deep Earth.
If you have ever watched the Ice Age films — enforced viewing, of course, courtesy of your children — you'll remember Manny the mammoth and Scrat the squirrel trudging across an endless white wilderness, the whole world locked under sheets of ice. Now that we know Oman is a geological paradise, here is perhaps its strangest exhibit: the country was once buried under glacial ice — not once, but at least three times. Drive out to the rock outcrops of the Huqf region — home to some of the oldest pages in Oman's 800-million-year archive — or the Dhofar Mountains, and you can run your fingers over the physical evidence of what scientists call 'Snowball Earth': periods, hundreds of millions of years ago, when ice gripped virtually the entire planet, from the poles all the way down to the equator. The clues are written in the stone: jumbled deposits called diamictites, boulders dropped by melting icebergs into ancient seabeds, and scratches gouged by glaciers grinding their way across land that today records some of the hottest temperatures on Earth.
The American humourist Ogden Nash, who rhymed his way through cows, camels and canaries, alas never versified about canyons. But had he stood at the rim of Jebel Shams and peered into Wadi Nakhr, he might have managed: 'The canyon's deep, the drop is vasty — / Looking down is rather ghasty.' He would not have been wrong. From the 3,000-metre summit of Jabal Shams, the land tumbles all the way down to the wadi floor — a descent to rival Arizona's Grand Canyon, the most photographed gorge on Earth.
Don't ever try recording an Instagram reel at the edge — you'll only discover that ancient, involuntary response: the knees soften, the stomach lifts, and the hand abandons the phone in search of something solid. Geologists, meanwhile, look down and see something else entirely. Those sheer cliff walls are a library — layer upon layer of folded marine limestone, each band a chapter written on the floor of a vanished tropical ocean, then heaved kilometres skyward by the patient, unstoppable collision of tectonic plates. The seabed, quite literally, went up in the world. Vasty and ghastly, yes — but also, page for page, one of the greatest books ever written in stone.
And at the country's northern tip, the museum saves its strangest exhibit: the Musandam Fjords. The jagged peninsula, with its maze of sea-filled inlets, is often called the Norway of Arabia — but the resemblance is a case of mistaken identity. Norway's fjords were carved by glaciers grinding their way to the sea; Musandam's were made by drowning. The Arabian Plate, on which every one of us sits, is slowly colliding with the Eurasian Plate to the north, and in that unhurried, unstoppable embrace, Musandam is being pushed downward. The old river valleys, flooded millimetre by millimetre by the advancing water, have become the spectacular khors where dhows now drift and dolphins escort the tour boats. Geologists call such a drowned valley a 'ria' — surely the shortest name for the longest sinking.
Some of the world's top geology departments make the pilgrimage to Oman a formal part of their degree programmes — as colleagues in the field often remind me, with just a hint of envy. While other students study textbook diagrams of the mantle, theirs fly here to stand on the real thing. So, the next time visitors ask what there is to see in Oman, resist the urge to list malls and beaches. Tell them the truth: the whole country is the exhibit — a museum with no roof, no ticket counter and no closing time, where you can touch the deep Earth before lunch and cruise a drowning coastline by sunset. Somewhere, surely, a geologist is already posting it: #BestMuseumOnEarth — no entry fee, 800 million years of history, parking available.