Answer:
There is a thing called a continental drift. It started about 200 million years ago. At first the continents were all attached, this super continent was called pangaea. Continental drift occurs because of the shift of the tectonic plates within the earth's outer shell. The heat from within the earth triggers movement to occur. This a very slow process though. It took 200 million years for the continents to get where the are now and would probably take another 200 to collide.