Alloy
A metal containing more than one type of metal atom.
Asthenosphere
The layer of the mantle that lies between 100-150km and 350km deep; the asthenosphere is relatively soft and can flow when acted on by force.
Atmosphere
A layer of gases that surrounds a planet.
Basalt
A fine-grained mafic igneous rock.
Core
The dense, iron-rich centre of the Earth.
Crust
The rock that makes up the outermost layer of the Earth.
Dipole
A magnetic field with a north and south pole, like that of a bar magnet.
Earthquake
A vibration caused by the sudden breaking or frictional sliding of rock in the Earth.
Fault
A fracture on which one body of rock slides past another.
Gabbro
A coarse-grained intrusive mafic igneous rock.
Geothermal gradient
The rate of change in temperature with depth.
Glass
A solid in which atoms are not arranged in an orderly pattern.
Granite
A coarse-grained intrusive silicic igneous rock.
Groundwater
Water that resides under the surface of the Earth, mostly in pores or cracks of rock or sediment.
Hydrosphere
The Earth's water, including surface water (lakes, rivers, and oceans), groundwater, and liquid water in the atmosphere.
Inner core
The inner section of the core 5,155km deep to the Earth's centre at 6,371km, and consisting of solid iron alloy.
Lithosphere
The relatively rigid, nonflowable, outer 100-150km thick layer of the Earth; constituting the crust and the top part of the mantle.
Lower mantle
The deepest section of the mantle, stretching from 670km down to the core-mantle boundary.
Magnetic field
The region affected by the force emanating from a magnet.
Magnetic field lines
The trajectories along which magnetic particles would align, or charged particles would flow, if placed in a magnetic field.
Mantle
The thick layer of rock below the Earth's crust and above the core.
Melts
Molten (liquid) rocks.
Metals
Solids composed almost entirely of atoms of metallic elements; they are generally opaque, shiny, smooth, and malleable, and can conduct electricity.
Mineral
A homogenous, naturally occurring, solid inorganic substance with a definable chemical composition and an internal structure characterised by an orderly arrangement of atoms, ions, or molecules in a lattice. Most minerals are inorganic.
Moho
The seismic-velocity discontinuity that defines the boundary between the Earth's crust and mantle.
Organic chemical
A carbon-containing compound that occurs in living organisms, or that resembles such compounds; it consists of carbon atoms bonded to hydrogen atoms along with varying amounts of oxygen, nitrogen, and other chemicals.
Outer core
The section of the core, between 2,900 and 5,150km deep, that consists of liquid iron alloy.
Periodotite
A coarse-grained ultramafic rock.
Rock
A coherent, naturally occurring solid, consisting of an aggregate of minerals or a mass of glass.
Sediment
An accumulation of loose mineral grains, such as boulders, pebbles, sand, silt, or mud, that are not cemented together.
Seismic waves
Waves of energy emitted at the focus of an earthquake.
Silicate minerals
Minerals composed of silicon-oxygen tetrahedra linked in various arrangements; most contain other elements too.
Topography
Variations in elevation.
Transition zone
The middle portion of the mantle, from 400 to 670km deep, in which there are several jumps in seismic velocity.
Upper mantle
The uppermost section of the mantle, reaching down to a depth of 400km.
Volatiles
Elements or compounds such as H20 and CO2 that evaporate easily and can exist in gaseous forms at the Earth's surface.
Mafic
A term used to describe magmas or igneous rocks that are rich in iron and magnesium, and relatively poor in silica.