The ocean basins are continuously changing today. Geological processes associated with the movement of Earth's tectonic plates are responsible for changing the size and shape of the world's ocean basins over time. The process of seafloor spreading is creating new basaltic ocean crust at the Mid-Atlantic Ridge in the Atlantic Ocean basin. Therefore, the Atlantic Ocean is slowly getting bigger. When new lithosphere is created at one point, it is simultaneously being destroyed at another location. This is happening at subduction zones, located at deep ocean trenches in the Pacific Ocean. Therefore, the Pacific Ocean basin is slowly shrinking over time.

During the time of Pangaea, there was one global ocean that surrounded the supercontinent, known as the Panthalassic Ocean. When Pangaea broke into the continents of Laurasia and Gondwanaland approximately 200 million years ago, the Panthalassic Ocean basin also changed. It was split into two oceans, the Pacific Ocean in the west and the Tethys Ocean (composed of today's Atlantic and Indian Oceans) in the east.