Earth's Structure, Plate Tectonics, and Geology
Core concepts
Earth has a crust, mantle, outer core, and inner core. The lithosphere is broken into tectonic plates that move on the asthenosphere. Divergent boundaries create new crust (mid-ocean ridges, rift valleys); convergent boundaries produce subduction, mountains, and volcanoes; transform boundaries cause earthquakes as plates slide. Seafloor spreading and magnetic striping support plate tectonics. Earthquakes release energy as seismic waves; P waves arrive first, S waves second. The rock cycle links igneous, sedimentary, and metamorphic rocks. Weathering, erosion, and deposition shape landforms.
Traps to watch
- Confusing the mantle with the lithosphere; the lithosphere includes crust and upper mantle.
- Thinking plates float on the outer core.
- Mixing up which boundary type causes which feature.
- Assuming S waves travel through liquids; they do not.
- Treating erosion and weathering as the same process.
Worked example
At an ocean-continental convergent boundary, the denser oceanic plate subducts, forming a trench and volcanic mountain chain. Shallow earthquakes occur near the trench; deeper ones follow the subducting slab.
Rule of thumb
Divergent = new crust; convergent = crust destroyed or mountains built; transform = sliding. Match boundary to feature before choosing an answer.