Key terms:
Asthenosphere
The upper layer of the earth’s mantle which is semi-molten and on which the plates float and move. It is located bellow the Lithosphere.
Collision boundary
Where two plates of continental crust move towards each other and collide creating fold mountains.
Conservative boundary
Where two plates move alongside each other. At this boundary crust is neither created nor destroyed but earthquakes usually occur here.
Constructive boundary
A constructive (tensional) plate boundary happens where plates move apart. Most of these plate margins are under the oceans. As the plates move apart, magma rises from the mantle to the earth's surface. the rising magma forms shield volcanoes.
Continental Crust
The relatively thick part of the earth's crust which forms the large land masses. It is generally older and more complex than the oceanic crust.
Continental drift
The gradual movement of the continents across the earth's surface through geological time.
Convection currents
The transfer of heat by movement of material within the mantle
Crust
The solid, outermost layer of the Earth.
Destructive boundary
Where two plates move towards each other. In the case of a plate consisting of continental crust meeting a plate consisting of oceanic crust, the oceanic crust will be subducted and destroyed as it is less dense.
Inner core
The Earth's inner core is the Earth's innermost part and it is thought to be primarily solid ball with a radius of about 1220 kilometres.
Lithosphere
The lithosphere is the rocky outer part of the Earth. It is made up of the brittle crust and the top part of the upper mantle.
Mantle
The portion of the earth, about 1800 miles (2900 km) thick, between the crust and the core.
Mesosphere
the solid part of the earth's mantle lying between the asthenosphere and the core
Oceanic Crust
The relatively thin part of the earth's crust which underlies the ocean basins. It is geologically young compared with the continental crust and consists of basaltic rock overlain by sediments.
Outer Core
The Earth's outer core is a liquid layer about 2,300 km (1,400 mi) thick and composed of iron and nickel .Its outer boundary lies 2,890 km (1,800 mi) beneath Earth's surface.
Paleomagnetism
The fixed orientation of a rock's magnetic minerals as originally aligned at the time of the rock's formation.
Plate tectonics theory
The lithosphere of the earth is divided into a small number of plates which float on and travel independently over the mantle and much of the earth's seismic activity occurs at the boundaries of these plates.
Sea floor spreading
The process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.