Sea-floor spreading was the first hard evidence of tectonic motions. Source of long-lasting volcanic activity far from any plate boundaries. As the plate slides over the fixed hot-spot, get long chains of shield volcanoes. The further along the chain you go, the older the island. Continental Drift Most dramatic manifestation of plate motions is the long-term Continental Drift.
Continents look like pieces of a large jigsaw puzzle.
Measure sea-floor spreading and plate motions at fault, can trace motions back in time. Plate Motions cause large-scale changes in the continents and oceans over millions of years. My geologist colleagues will likely be most upset with me for having compressed their life's work into one brief lecture. The subject is rich and fascinating, but what I want to emphasize here are the basic processes at work in the interior of our planet. When we consider the other terrestrial planets in the Solar System, we will return to these ideas, and see how they are similar and different from the Earth.