Around 80 km up, far above all other clouds, thin bluish veils sometimes form: noctilucent clouds. They are ice crystals clinging to dust, part of it left by meteors. Still lit by the Sun after it has set, they shine in summer twilight skies at high latitudes. They were first described only in 1885, two years after the Krakatoa eruption.
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.