Actually, these what you call land masses are the PLATES. These plates are moving in about 5 centimeters or 2 inches a year. These were believed to be only one supercontinent called PANGEA. But because of climate change and its movements, this supercontinent was then divided into two. The Lauresia in the northern hemisphere and Gondwana in the southern hemisphere. Millions of years later, these plates move and been able to look like what the world is used to be right now.
And many scientists believe that these plates are still moving and moving.