There are seashells on top of Everest. Here's why.

The summit of Mount Everest is made of marine limestone. If you chipped away at the world’s highest peak, you would find the fossilized remains of brachiopods, crinoids, and trilobites—creatures that lived at the bottom of the sea 450 million years ago.

These fossils sit five miles above sea level because the Himalayan mountains didn't always exist. About 50 million years ago, the tectonic plate carrying India slammed into Asia with such force that it crumpled the ancient Tethys Ocean floor, thrusting the seabed into the sky. The rock at the very tip of the mountain is officially known as the Qomolangma Formation.

Despite the freezing winds and lack of oxygen, this rock layer is identical to limestone found in shallow, tropical waters today. Over millions of years, the ocean floor was folded and pushed upward by about 10 millimeters every year.

This means the mountain is still growing. As plates continue to collide, the ancient sea floor rises higher and higher, even as erosion tries to pull it back down. The highest point on our planet is quite literally a graveyard for ancient shrimp.

Curiously, yellow bands of siltstone visible just below the summit contain fossils of tiny sea lilies, proving the entire peak was once a calm, sunlit reef.