PART 1 - GEOLOGICAL ACTIVITY
PART 2: MILESTONES IN THE EARTH EVOLUTION
A subduction zone is a region of the earths crust where tectonic plates meet. The places where these plates meet are called tectonic boundaries. An oceanic plate can descend beneath another oceanic plate - Japan, Indonesia, and the Aleutian Islands are examples of this type of subduction. A oceanic plate can also decend beneath a continental plate - South America, Central America, and the cascade volcanoes are an example of this type of subduction.
Seafloor spreading is a geologic process in which tectonic plates—large slabs of Earth's lithosphere—split apart from each other. Sea floor spreading and other tectonic activity processes are the result of mantle convection. Seafloor spreading occurs along mid-ocean ridges—large mountain ranges rising from the ocean floor. The Mid-Atlantic Ridge, separates the North American plate from the Eurasian plate, and the South American plate from the African plate. The East Pacific Rise is a mid-ocean ridge that runs through the eastern Pacific Ocean and separates the Pacific plate from the North American plate.