Plate Tectonics

Question 1

Asthenosphere

Answer 1

The upper zone of Earth’s mantle, located directly below the lithosphere; a hot, slowly flowing layer of relatively weak rock that allows for the movement of the tectonic plates.

Question 2

Continental drift

Answer 2

Movement of continents in response to seafloor spreading; the most recent episode of continental drift supposedly began about 200 million years ago with the breakup of the supercontinent Pangaea.

Question 3

Convection

Answer 3

Transfer of heat involving movement of particles; for example, the boiling of water, in which hot water rises to the surface and displaces cooler water that moves toward the bottom.

Question 4

Convergent boundary

Answer 4

Boundary between two lithospheric plates in which one plate descends below the other (subduction).

Question 5

Core

Answer 5

With respect to the interior of Earth, the central part of Earth below the mantle, divided into a solid inner core with a radius of approximately 1300 km and a molten outer core with a thickness of about 2000 km; the core is thought to be metallic and composed mostly of iron.

Question 6

Crust

Answer 6

The outermost layer of the solid Earth, embedded in the top of the lithosphere, that varies in thickness from 6 to 7 km below the oceans to as much as 70 km beneath continental mountain ranges.

Question 7

Divergent boundary

Answer 7

Boundary between lithospheric plates characterized by production of new lithosphere; found along oceanic ridges.

Question 8

Hot spot

Answer 8

Assumed stationary heat source located below the lithosphere that feeds volcanic processes near Earth’s surface.

Question 9

Isostasy

Answer 9

The principle stating that thicker, more buoyant crust is topographically higher than crust that is thinner and denser. Also, with respect to mountains, the weight of rocks of the upper crust is compensated by buoyancy of the mass of deeper crystal rocks; that is, mountains have “roots” of lighter crustal rocks extending down into the denser mantle rocks, like icebergs in the ocean.

Question 10

Lithosphere

Answer 10

Outer layer of Earth, approximately 100 km thick, that comprises the plates that contain the ocean basins and continents.

Question 11

Magnetic reversal

Answer 11

Involves the change of Earth’s magnetic field between normal polarity and reverse polarity; also sometimes known as geomagnetic reversal.

Question 12

Mantle

Answer 12

An internal layer of Earth approximately 3000 km thick composed of rocks that are primarily iron and magnesium-rich silicates. The lower boundary of the mantle is with the core, and the upper boundary is with the crust. The boundary is known as the Mohorovicˇic´ discontinuity (also called the Moho).

Question 13

Mid-oceanic ridge

Answer 13

A topographic high commonly found in the central part of oceans characterized by seafloor spreading. An example is the Mid-Atlantic Ridge.

Question 14

Moho

Answer 14

The boundary between the crust and mantle, also known as the Mohorovicˇic´ discontinuity; distinguished by compositional differences between the rocks of the crust and the mantle.

Question 15

Paleomagnetic

Answer 15

Also known as paleomagnetism; refers to the study of magnetism of rocks and the intensity and direction of the magnetic field of Earth in the geologic past.

Question 16

Plate tectonics

Answer 16

model of global tectonics that suggests that the outer layer of Earth, known as the lithosphere, is composed of several large plates that move relative to one another; continents and ocean basins are passive riders on these plates.

Question 17

Seafloor spreading

Answer 17

The plate tectonics concept that new crust is continuously added to the edges of lithospheric plates at divergent plate boundaries as a result of upwelling of magma along mid-oceanic ridges.

Question 18

Seismology

Answer 18

The study of earthquakes as well as the structure of Earth through the evaluation of both natural and artificially generated seismic waves.

Question 19

Spreading center

Answer 19

Synonymous with mid-oceanic ridges where new crust is continuously added to the edges of lithospheric plates.

Question 20

Subduction zone

Answer 20

Convergence of tectonic plates where one plate dives beneath another and is consumed in the mantle.

Question 21

Submarine trench

Answer 21

A relatively narrow, long (often several thousand km), deep (often several km) depression on the ocean floor that forms as a result of convergence of two tectonic plates with subduction of one.

Question 22

Transform boundary

Answer 22

Synonymous with transform faults, occurring where edges of two plates slide past one another; most are boundaries within oceanic crust; an example on land is the San Andreas fault in California.

Question 23

Triple junction

Answer 23

Areas where three tectonic plates and their boundaries join

Question 24

Wadati-Benioff zone

Answer 24

Inclined zone of earthquakes produced as a tectonic plate is subducted.

Question 25

Wilson Cycle

Answer 25

The cyclic nature of plate tectonics

Question 26

Usually oceanic (Divergent)

Answer 26

Spreading. The two plates move away from one another, and molten rock rises up to fill the gap.

Question 27

Ocean–continent (Convergent)

Answer 27

Oceanic plate sinks beneath continental plate.

Question 28

Ocean–ocean (convergent)

Answer 28

Older, denser, oceanic plate sinks beneath the younger, less dense oceanic plate.

Question 29

Continent–continent (Convergent)

Answer 29

Neither plate is dense enough to sink into the asthenosphere; compression results.

Question 30

Ocean–ocean or continent–continent (Transform)

Answer 30

The plates slide past one another.