Did you know that the deepest point in the world's oceans is called "Challenger Deep", and that it is named after the HMS Challenger that discovered the general area? The ship's crew did this with a lead line - or a very VERY long rope with a chunk of lead (pb) attached to the end.
Before the underwater survey was done (in the golden age of sail, then the sun never set on the British Empire) it was thought that the open sea bottom was flat and featureless. Nobody had any idea there were mountain ranges, trenches, and other shit.
The HMS Challenger survey was supposed to confirm this belief. Well, it failed its mission and discovered the Mariana Trench (the trench where Challenger Deep is found).
And why do I know this? Who the hell knows. I just do. I try to rot my brain by watching Cartoon Network - but it is clearly not working out too well.