Hundreds of millions of years ago the continents were joined together in a super-continent that scientists call Pangaea. It means "all lands" in Greek. It stretched all the way from the North to the South Pole, but that's not the way the earth looks now, obviously. What happened?
Continental drift. As you know, the earth's crust is always on the move. Over millions of years Pangaea broke apart. However, if continental and oceanic crust are still drifting, the earth won't always look like it does now. I wonder how it will look in another hundred million years?
Well, scientists have some predictions. The Atlantic Ocean will be lot bigger, and the Pacific, smaller. The Mediterranean Sea may be gone, and Africa and Europe will be connected. India will probably push its way up into Southern Asia, meaning that the Himalayan Mountains will be pushed up even taller than they already are. Los Angeles may migrated north and bump into San Francisco!