Science Puzzle
How Did Seashells Get to the Top of Everest?
The rock at the very top of Mount Everest, 8,849 metres above sea level, is a pale limestone. Inside it geologists have found fragments of trilobites, sea lilies and tiny shelled creatures called ostracods: animals that only ever lived in the sea.
How did the remains of sea creatures end up on top of the highest mountain on Earth?
The Answer
The sea didn't climb the mountain. The seabed was pushed up into the sky.
The summit limestone began forming around 450 million years ago on the floor of a warm, shallow sea. Shells and skeletons of sea creatures piled up on the seabed with fine mud. Over millions of years they were buried, squeezed and hardened into rock. That seabed lay on the edge of the slab of Earth's crust that carries India.
Earth's surface is broken into huge plates that move a few centimetres a year. Over tens of millions of years the Indian plate drifted north, and about 50 million years ago it began colliding with Asia. Continental crust is too thick and light to sink back into the mantle, so instead of one plate sliding neatly under the other, the crust crumpled. Rock was folded, broken and stacked up in enormous slices, and old seabed rock was lifted thousands of metres into the air to form the Himalaya.
The collision hasn't finished. India is still pushing north at around 4 to 5 centimetres a year, and the Himalaya are still rising, though wind, ice and rivers wear them down at the same time.
The principle: Mountain building at colliding plates. When two continents collide, their crust is folded and pushed upwards, so rock that formed on an ancient seabed can end up thousands of metres above sea level.