Earth constantly releases about 44 terawatts of heat from its depths. In 2011, a neutrino detector in Japan picked up 'geoneutrinos', particles emitted by decaying uranium and thorium in rocks. Their numbers suggest that about half of that heat comes from natural radioactivity; the rest is primordial heat left over from the planet's formation.
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.