The rocks at the top of Mount Everest are limestones that formed more than 450 million years ago on the floor of a warm sea. They contain fossils of trilobites, crinoids and other marine creatures. The collision between India and Asia, which began about 50 million years ago, lifted these old sediments to nearly 8,850 m.
On 27 August 1883, the eruption of the Indonesian volcano Krakatoa was heard as far away as Rodrigues Island, nearly 4,800 km away. Its pressure wave was picked up by barometers worldwide and circled the globe several times. The tsunamis that followed killed more than 36,000 people.
The deepest known point in the ocean, Challenger Deep, lies roughly 10,900 m below the Pacific surface. Drop Everest in and its summit would still sit about 2 km underwater. Down there, the pressure is more than 1,000 times what you feel at sea level, roughly a tonne pressing on every square centimetre.