The interior of Earth is hot. Heat flow and movement of material within Earth cause sections of Earth's crust to move. This may result in earthquakes, volcanic eruption, and the creation of mountains and ocean basins.
Analysis of earthquake wave data (vibrational disturbances) leads to the conclusion that there are layers within Earth. These layers - the crust, mantle, outer core, and inner core - have distinct properties.
Folded, tilted, faulted, and displaced rock layers suggest past crustal movement.
Continents fitting together like puzzle parts and fossil correlations provided initial evidence that continents were once together.
The Theory of Plate Tectonics explains how the "solid" lithosphere consists of a series of plates that "float" on the partially molten section of the mantle. Convection cells within the mantle may be the driving force for the movement of the plates.
Plates may collide, move apart, or slide past one another. Most volcanic activity and mountain building occur at the boundaries of these plates, often resulting in earthquakes.
Rocks are classified according to their method of formation. The three classes of rocks are sedimentary, metamorphic, and igneous. Most rocks show characteristics that give clues to their formation conditions.
The rock cycle model shows how types of rock or rock material may be transformed from one type of rock to another.
Analysis of seismic waves allows the determination of the location of earthquake epicenters, and the measurement of earthquake magnitude; this analysis leads to the inference that Earth's interior is composed of layers that differ in composition and states of matter.
The outward transfer of Earth's internal heat drives convective circulation in the mantle that moves the lithospheric plates comprising Earth's surface.
These plate boundaries are the sites of most earthquakes, volcanoes, and young mountain ranges.
Compared to continental crust, ocean crust is thinner and denser. New ocean crust continues to form at mid-ocean ridges.
Earthquakes and volcanoes present geologic hazards to humans. Loss of property, personal injury, and loss of life can be reduced by effective emergency preparedness.
Many processes of the rock cycle are consequences of plate dynamics. These include the production of magma (and subsequent igneous rock formation and contact metamorphism) at both subduction and rifting regions, regional metamorphism within subduction zones, and the creation of major depositional basins through down-warping of the crust.
Many of Earth's surface features such as mid-ocean ridges/rifts, trenches/subduction zones/island arcs, mountain ranges (folded, faulted, and volcanic), hot spots, and the magnetic and age patterns in surface bedrock are a consequence of forces associated with plate motion and interaction.
Plate motions have resulted in global changes in geography, climate, and the patterns of organic evolution.