How is it possible that fossils have been on top of Mount Everest?

There are sea fossils on Mount Everest because it is thought that the summit of Mount Everest started at the bottom of the ancient Tethys Sea, the motion of the Indian subcontinental plate and the urasian continental plate colliding, about 30 - 50 million years ago, caused the mountain to rise up and become the highest mountain on the Earth.