Tectonic activity causes continental drift to occur on the Earth's surface. National Geographic explains that continents rest upon massive slabs of rock called tectonic plates. Over the course of millions of years, tectonic activity shifts these plates and rearranges the accompanying landmasses.
Scientists theorize that 200 million years ago, all of Earth's current continents were joined as a single landmass known as Pangaea. Within the seafloor of the oceans, tectonic plates move apart and molten rock rises from within the Earth and forms new crust material. As seafloor spreading continues and the ocean floors grows wider, continents on opposite sides move further away from each other. North America and Europe move away from each other at a rate of approximately 1 inch per year.