Over Earth's history, the magnetic field has reversed hundreds of times, with magnetic north becoming south and vice versa. Reversals happen at highly irregular intervals, from tens of thousands to tens of millions of years apart. The last one was about 780,000 years ago: back then, a compass needle would have pointed south.
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.