Plate Tectonics

Alfred Wegener

A German scientist who proposed the theory of continental drift

Harry Hess

A naval scientist who proposed the theory of sea-floor spreading

evidence for Alfred Wegener's theory of continental drift

Fossil Evidence, Fit of the Continents

evidence for Harry Hess' theory of seafloor spreading

Magnetic Striping, Age of Seafloor, Sediment Thickness

magnetic striping

The pattern of alternating normal and reversed magnetic polarities found in the seafloor on either side of the spreading center.

Magnetite

magnetic material found in the seafloor

continental crust

crust that lies beneath the Earth's continents and is about 25-70 km thick. Less dense.

oceanic crust

crust that lies beneath the ocean and is usually 7-10 km thick. More dense.

convergent boundary

A plate boundary where two plates move toward each other.

oceanic trench

Deep, narrow trough in the ocean floor where subduction is taking place.

Subduction

The process by which one plate is pushed underneath another plate at a convergent boundary

volcanic island arc

a series of volcanoes formed at a subduction zone at a oceanic-oceanic convergent boundary.

divergent boundary

A plate boundary where two plates move away from each other.

Rifting

the process by which Earth's crust breaks apart; can occur within continental crust or oceanic crust

mid-ocean ridge

An underwater mountain chain where new ocean floor is formed

transform boundary

A plate boundary where two plates move past each other in opposite directions

fault line

a crack in Earth's surface caused by moving plates

Mantle

The layer of hot, solid material between Earth's crust and core.

Magma

A molten mixture of rock-forming substances, gases, and water from the mantle

slab pull

the pulling of a tectonic plate as its edge subducts deep into the mantle

ridge push

when the force of gravity moves a plate downward and away from a ridge

Volcanoes

an opening in the Earth's crust through which molten lava, ash, and gases are ejected.

Ring of Fire

A zone of intense volcanic activity at the boundary between the Pacific plate and surrounding continental plates

Focus

The point beneath Earth's surface where rock breaks under stress and causes an earthquake

Epicentre

the point on the Earth's surface directly above the focus of an earthquake

Seismometer

Instrument used to measure horizontal or vertical motion during an earthquake.

P (primary) waves

longitudinal waves (back and forth) that travel fast.

S (secondary) waves

transverse waves (up and down) travel slower than P-waves.

surface waves

seismic waves that travel along the Earth's surface. Causes the most destruction.

earthquake

The shaking that results from the movement of rock beneath Earth's surface.

Richter scale

A scale that rates an earthquake's magnitude based on the size of its seismic waves.

tectonic plates

Sections of the Earth's crust that move due to convection currents.

plate boundary

the region where two tectonic plates are in contact

Hot spot

A localized area where magma from deep in the mantle rises, not necessarily associated with a plate boundary

Continental-Continental

Pushed upwards forming large mountain ranges e.g Himalayas

Oceanic-Continental

Creates fold mountains and active volcanoes e.g. Ring of Fire

Subduction

Denser Oceanic crust is pushed underneath the Continental crust. Creates deep trenches

Oceanic-Oceanic

Faster plate undergoes subduction. Creates deep trenches and island arcs from underwater volcanoes.