A tectonic plate is a piece of the Earth's crust.
Tectonic plates move around because of convection currents in part of the deep interior of the earth that's called the mantle. When tectonic plates collide or are drawn apart, they form boundaries, which can be rift valleys or mountains or ridges at the bottoms of oceans. Tectonic plates can also cause earthquakes when they slip past each other.
Over millions and hundreds of millions of years areas which were very close together can become thousands of miles or kilometres apart. Similarly areas which were thousands of kilometres apart can move close together.
Despite what some crazy or misinformed people say the Earth is four thousand million years old and tectonic plates have been moving round most of that time.
- Earth 100 Million Years From Now This shows how the Earth changed and will change.