Science: Plate Tectonics: Standard Practice

# Medium Level Guide Grade-level practice aligned to typical classroom expectations and unit assessments. # Layers of the Earth Earth has a crust, mantle, and core. The lithosphere includes the crust and upper mantle and is broken into tectonic plates. The asthenosphere below is partially molten and allows plates to move slowly on convection currents. # Continental Drift and Sea-Floor Spreading Alfred Wegener proposed that continents once fit together as Pangaea. Evidence includes fossil matches and rock layers across oceans. Sea-floor spreading at mid-ocean ridges pushes plates apart and creates new crust. # Types of Plate Boundaries Divergent boundaries move apart (mid-ocean ridges, rift valleys). Convergent boundaries collide (mountains, subduction, trenches). Transform boundaries slide past each other (earthquakes along faults like the San Andreas). # Earthquakes and Volcanoes Most earthquakes and volcanoes occur near plate boundaries. Stress builds until rocks break along faults, releasing seismic waves. Volcanoes form where magma reaches the surface, often at subduction zones and hot spots.