The Andes Mountains formed along the western coast of South America over the past 25 million years as the Nazca plate collided with and subducted under the South American plate, pushing up the various sedimentary, igneous, and metamorphic rock layers in a process of volcanism and uplift. The central Andes are estimated to be around 10 million years old, while different parts of the overall mountain range developed at different times over the millions of years of plate convergence and mountain building.