Why there are seashells at the top of Mount Everest, and where you can see them

The top of Mount Everest is a band of limestone that formed on the floor of a warm, shallow sea about 450 million years ago, and it is full of the fossils of the animals that lived there. The highest rock on Earth is not granite or basalt. It is a seabed, lifted 8,849 metres into the sky by two continents that are still colliding.

What the summit is actually made of

Limestone laid down on the bed of the Tethys, an ocean that no longer exists. Geologists call the summit layer the Qomolangma Formation, after Everest’s Tibetan name, and it forms roughly the top 125 metres of the mountain.

The International Union of Geological Sciences lists the Ordovician rocks of Everest among its global geoheritage sites. They date from the Great Ordovician Biodiversification Event, one of the most important bursts of diversification in the history of marine life, when this stretch of crust sat on a warm shelf near the equator. Climbers have photographed fossil-bearing beds around 8,500 metres, and researchers at Montana State University report fossil fragments in rock sampled within about six metres of the true summit.

The climber who found the first fossils

Noel Odell, the geologist on the 1924 British expedition, found them — on the same expedition that lost George Mallory and Andrew Irvine. Odell was the last man to see the two alive, climbing through drifting cloud high on the mountain.

Scouting above 25,500 feet, about 7,770 metres, he came across a band of pale limestone. “At about 25,500 feet I came upon a limestone band which to my joy contained fossils,” he wrote, “the first definite forms found on Everest.” Mallory’s body was not found until 1999; Irvine’s remains surfaced only recently — see the boot that melted out of Everest’s ice.

How a seafloor ends up 8,849 metres in the air

India crashed into Asia and the seabed between them had nowhere to go but up. After the supercontinent Pangea broke apart about 200 million years ago, the Indian plate drifted north across the Tethys and, around 55–50 million years ago, met Asia.

Neither plate could sink beneath the other in the usual way, so the crust between them was folded, cracked and stacked upward until the old seabed became the highest exposed rock on the planet. The collision has not stopped: India still pushes north by a few centimetres a year, and Everest is still rising by a few millimetres a year — with, it turns out, help from a river that changed course. The age of the summit rock was pinned down in the 1970s and later confirmed by researchers including David Harper of Durham University.

The Yellow Band you can see from the trail

You cannot touch the summit rock without climbing Everest, but you can see the ocean from Kala Patthar. The pale stripe that rings the upper mountain below the summit pyramid is the Yellow Band, altered marine limestone roughly 172 metres thick that contains up to 5 percent crinoid fragments, according to Montana State University’s Everest education project.

From Kala Patthar, at 5,545 metres above Gorak Shep, it is plainly visible on a clear morning. Guides on a well-run trek will also point out the folded, layered rock bands above Dingboche and Lobuche — the same upheaval, at trekking altitude.

Where trekkers can hold the ocean

In the Kali Gandaki valley, where fossil ammonites turn up in the riverbed. Nepalis call them shaligram, and Hindus and Buddhists venerate them as a living form of Vishnu.

They are younger than Everest’s summit — Jurassic, about 140 million years old, from a later stage of the same long-lived Tethys — and far easier to reach, on the trail to Muktinath through the world’s deepest gorge.

Sources: International Union of Geological Sciences Geoheritage, “The Ordovician Rocks of Mount Everest”; Montana State University, Everest Education Expedition; BBC Science Focus.

Cover photo: Abdul Kayum via Pexels (Pexels License). Section photos: Jasper Hunter via Pexels (Pexels licence); Elle Hughes via Pexels (Pexels licence); Balazs Simon via Pexels (Pexels licence).