Plate Tectonics:
* Earth's outer layer is composed of rigid plates called tectonic plates.
* These plates are constantly moving, driven by convection currents in the mantle (the layer beneath the crust).
* Convection currents: Heat from the Earth's core causes molten rock in the mantle to rise. As it cools, it sinks, creating a circular flow.
* Seafloor Spreading: Where plates move apart (divergent plate boundaries), molten rock rises from the mantle and erupts, creating new oceanic crust. This process is called seafloor spreading.
* Subduction: Where plates collide (convergent plate boundaries), one denser plate (usually oceanic) slides beneath the other (subduction). The subducted plate melts as it descends into the mantle.
How Subduction and Seafloor Spreading Are Connected:
1. Seafloor Spreading: New oceanic crust is constantly being created at mid-ocean ridges, pushing older crust away from the ridge.
2. Subduction: As older oceanic crust moves away from the ridge, it cools and becomes denser. Eventually, it collides with a continental plate or another oceanic plate.
3. The denser plate subducts: The denser plate (usually the oceanic one) dives beneath the other, melting and creating volcanoes and mountain ranges.
In summary, plate tectonics is the driving force behind both seafloor spreading and subduction. Convection currents in the mantle cause the plates to move, which leads to the creation and destruction of Earth's surface.
