Drain the Oceans
How quickly would the ocean's drain if a circular portal 10 meters in radius leading into space was created at the bottom of Challenger Deep, the deepest spot in the ocean? How would the Earth change as the water is being drained? –Ted M.
What happens to the Earth? Not much. It would actually take hundreds of thousands of years for the ocean to drain. (…) When you started, the water level would drop by less than a centimeter per day. There wouldn't even be a cool whirlpool at the surface—the opening is too small and the ocean is too deep.  (It's the same reason you don't get a whirlpool in the bathtub until the water is more than halfway drained.)
Let's take a look at how the map would change.
And after 2000 years of trying to hold back the sea, the Netherlands are finally high and dry. No longer living with the constant threat of a cataclysmic flood, they're free to turn their energies toward outward expansion. They immediately spread out and claim the newly-exposed land.
This is what the map looks like when the drain finally empties. There's a surprising amount of water left,although much of it consists of very shallow seas, with a few trenches where the water is as deep as four or five kilometers.
Vacuuming up half the oceans would massively alter the climate and ecosystems in ways that are hard to predict. At the very least, it would almost certainly involve a collapse of the biosphere and mass extinctions at every level.
But it's possible—if unlikely—that humans could manage to survive. If we did, we'd have this to look forward to: