seismic waves
Vibrations that travel through Earth carrying the energy released during an earthquake.
lithosphere
A rigid layer made up of the uppermost part of the mantle and the crust.
inner core
A dense sphere of solid iron and nickel at the center of Earth.
pressure
The force exerted on a surface divided by the total area over which the force is exerted.
asthenosphere
The soft layer of the mantle on which the lithosphere floats.
crust
The layer of rock that forms Earth's outer surface.
mantle
The layer of hot, solid material between Earth's crust and core.
outer core
A layer of molten iron and nickel that surrounds the inner core of Earth.
radiation
The direct transfer of energy through space by electromagnetic waves.
density
The amount of mass of a substance in a given volume; mass per unit volume.
conduction
The direct transfer of heat between two substances that are touching.
convection current
The movement of a fluid (caused by differences in temperature) that transfer heat from one part of the fluid to another.
convection
The transfer of heat by the movement of a fluid.
continental drift
The hypothesis that the continents slowly move across Earth's surface.
Pangaea
Landmass that broke apart two hundred million years ago and gave rise to today's continents.
fossil
A trace of an ancient organism that has been preserved in rock.
mid-ocean ridge
An undersea mountain chain where new ocean floor is produced.
deep-ocean trench
A deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle.
sonar
A device that determines the distance of an object under water by recording echoes of sound waves.
subduction
The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a colliding plate boundary.
sea floor spreading
The process by which molten material adds new oceanic crust to the ocean floor.
plate
A section of the lithosphere that slowly moves over the asthenosphere, carrying pieces of continental and oceanic crust.
spreading boundary
A place where two plates move away from each other.
colliding boundary
Also called a convergent boundary - a place where two plates come together or collide.
plate tectonics
The theory that pieces of Earth's lithosphere are in constant motion, driven by convection currents in the mantle.
fault
A break or crack in Earth's lithosphere along which the rocks move.
rift valley
A deep valley that forms when two plates move apart.
sliding boundary
A place where two plates move past each other, moving in opposite directions.