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