Tectonic plates move a few centimetres a year, roughly the rate at which your fingernails grow. It sounds trivial, but it adds up: the Atlantic widens by about 2.5 cm a year, so it is now around a dozen metres wider than it was five centuries ago. Over 100 million years, that is enough to open an entire ocean.
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.