SIO 10 - The Earth (CH 3)

Supercontinent

A very large continent formed by the suturing together of smaller continents. (page 67)

Pangaea

A supercontinent that assembled at the end of the Paleozoic Era. (page 67)

Continental drift

The hypothesis that continents have moved and are still moving slowly across the Earth's surface. (page 68)

Bathymetry

Variation in depth. (page 72)

Abyssal plain

A broad, relatively flat region of the ocean that lies at least 4.5 km below sea level. (page 72)

Mid-ocean ridge

A 2-km-high submarine mountain belt that forms along a divergent oceanic plate boundary. (page 72)

Ridge axis

The crest of a mid-ocean ridge; the ridge axis defines the position of a divergent plate boundary. (page 74)

Fracture zone

A narrow band of vertical fractures in the ocean floor; fracture zones lie roughly at right angles to a mid-ocean ridge, and the actively slipping part of a fracture zone is a transform fault. (page 74)

Trench

A deep, elongate trough bordering a volcanic arc; a trench defines the trace of a convergent plate boundary. (page 74)

Volcanic arc

A curving chain of active volcanoes formed adjacent to a convergent plate boundary. (page 74)

Seamount

An isolated submarine mountain. (page 74)

Heat flow

The rate at which heat rises from the Earth's interior up to the surface. (page 75)

Seismic belt

The relatively narrow strips of crust on the Earth under which most earthquakes occur. (page 75)

Seafloor spreading

The gradual widening of an ocean basin as new oceanic crust forms at a mid-ocean ridge axis and then moves away from the axis. (page 76)

Subduction

The process by which one oceanic plate bends and sinks down into the asthenosphere beneath another plate. (page 76)

Paleomagnetism

The record of ancient magnetism preserved in rock. (page 77)

Magnetic declination

The angle between the direction a compass needle points at a given location and the direction of true north. (page 77)

Magnetic inclination

The angle between a magnetic needle free to pivot on a horizontal axis and a horizontal plane parallel to the Earth's surface. (page 77)

Paleopole

The supposed position of the Earth's magnetic pole in the past, with respect to a particular continent. (page 78)

Apparent polar-wander path

A path on the globe along which a magnetic pole appears to have wandered over time; in fact, the continents drift, while the magnetic pole stays fairly-fixed. (page 80)

Normal polarity

Polarity in which the paleomagnetic dipole has the same orientation as it does today. (page 81)

Reversed polarity

Polarity in which the paleomagnetic dipole points north. (page 81)

Magnetic-reversal chronology

The history of magnetic reversals through geologic time. (page 81)

Chron

The time interval between successive magnetic reversals. (page 81)

Subchron

Short-duration intervals of opposite polarity. (page 81)

Magnetic anomaly

The difference between the expected strength of the Earth's magnetic field at a certain location and the actual measured strength of the field at that location. (page 83)

Marine magnetic anomaly

The difference between the expected strength of the Earth's main dipole field at a certain location on the sea floor and the actual measured strength of the magnetic field at that location. (page 83)