As folks in the industry like to say, the Internet is a network of networks. To help get Web traffic from here to Britain or China, you need lots of companies with lots of money to build lots of wires to carry that data. And all those fiber optic cables run across the ocean floor, where they have to survive cold, currents, pressure and the occasional snagging by passing vessels or damage by earthquake.
Since 1989, the world has built 5.3 million miles' worth of underwater cabling. By 2017, we're expected to have completed nearly 850 separate cables across the globe. Two of these are partly owned by some of the biggest Internet companies in the world, Facebook and Google. The marketing firm Builtvisible took all this public data and turned it into an interactive map (not to mention a, well, deep history of underwater Internet cables). Here's what 25 years of Internet development looks like, in 1 GIF. (And here, by the way, is how you fix a damaged underwater cable.)