The Highest Point on Earth Used to Be the Bottom of the Sea

Everest's summit is not, geologically speaking, a mountain top. It is a slab of ocean floor, 450 million years old, thrust 8,848.86 metres into the sky by two continents that are still colliding beneath it — and the mountain is still rising to meet the fossils embedded in its own summit rock.

The rock was identified almost exactly a century ago, by a geologist remembered for almost nothing else. Noel Odell was the oxygen officer on the 1924 British Everest expedition, the one that lost George Mallory and Andrew Irvine somewhere near the top, and Odell was the last man to see them alive, climbing strong through drifting cloud on June 8th. What gets forgotten is that Odell was also a trained geologist, and on that same expedition he collected rock samples from the upper mountain, around 7,770 metres. What he carried down changed how scientists read the Himalaya.

A warm sea, 450 million years before anyone climbed anything

The samples were limestone, the kind of rock that forms only from compressed shell, coral and marine sediment in warm, shallow water. Geologists later named the summit pyramid's uppermost layer the Qomolangma Formation, after Everest's Tibetan name. It dates to the Ordovician period, roughly 450 million years ago, when the rock that would become the roof of the world was seabed on the floor of the Tethys Ocean, nowhere near land, half a planet away from where it sits today.

Inside that limestone, climbers and scientists have since documented the fossilised remains of trilobites (armoured sea arthropods extinct long before the dinosaurs), crinoids or sea lilies (stalked relatives of starfish), and ostracods (seed-sized shelled crustaceans easy to miss without a hand lens). Some of the clearest fossil-bearing samples have come from within about 6 metres of Everest's true summit, meaning a climber standing on top of the world, exhausted and short of oxygen, is standing almost directly on top of creatures that died 450 million years ago.

The seabed did not climb the Himalaya on its own. Around 55 million years ago, the Indian tectonic plate, then still an island adrift in the ocean, slammed into Asia. It has not stopped. India continues to push north at roughly 5cm a year, and while most of that force is absorbed sideways, enough is redirected upward to add about 4mm to Everest's height every year. The mountain that holds the fossils of an ancient sea is, slowly and measurably, still being built by the same collision that lifted them out of it.

What this means for trekkers

Odell's expedition has its own postscript worth knowing before you go. Mallory's body was not found until 1999, and Irvine's ice axe, and possibly his boot, only surfaced from the retreating glacier in the past two years (see our earlier report on the boot that melted out of Everest's ice). Odell spent the rest of his long life defending his claim that he saw the two men alive, high and moving fast, before cloud closed over them. The same expedition that lost two climbers on the summit ridge also proved, almost by accident, that the summit itself used to be underwater.

For trekkers heading to Gokyo or the classic Everest viewpoints, the takeaway is simple: the Himalaya is not a static wall. It's the visible, ongoing record of two continents still colliding, and it's a few millimetres taller than it was when you started reading this.

Source: Montana State University, Everest Education Expedition — Summit Limestone.

Cover photo: Mount_Everest_as_seen_from_Drukair2.jpg: shrimpo1967 derivative work: Papa Lima Whiskey 2 (talk) via Wikimedia Commons (CC BY-SA 2.0).