Chapter 3 - Earth Structure & Plate Tectonics

Density Stratification

the formation of layers in a material, with each deeper layer being denser than the unit above

2.7 g/cm³

Density of granite:

JOIDES Resolution

a 1978 research vessel that drills into the ocean floor to collect and study core samples.

Seismic Wave

a low frequency wave generated by the forces that cause earthquakes

S-Wave

secondary wave; a transverse wave that is associated with an earthquake and cannot move through liquid

P-Wave

primary wave; a compressional wave that is associated with an earthquake and can move through both liquid and rock

Seismograph

an instrument that detects and records earth movement associated with earthquakes and other disturbances

Differing density

Seismic waves travel at different speeds inside the Earth because of:

Shadow Zone

the wide band at Earth’s surface 105 degrees to 143 degrees away from an earthquake in which seismic waves are absent

Refracted

P-Waves are _____ by Earth’s liquid outer core:

Stopped

S-Waves are _____ by Earth’s liquid outer core:

Crust

the outermost solid layer of the Earth, composed mostly of granite and basalt

Oceanic Crust

the outermost solid surface of Earth beneath ocean floor sediments, primarily composed of basalt

Continental Crust

the solid masses of the continents, composed primarily of granite

Mantle

the layer of the Earth between the crust and the core, composed of silicates of iron and magnesium

Core

the innermost layer of the Earth, composed primarily of iron, with nickel and heavy elements

Lithosphere

the brittle, relatively cool outer layer of Earth, consisting of oceanic and continental crust and the outermost, rigid layer of the mantle

Asthenosphere

the hot, plastic layer of the upper mantle below the lithosphere

Lower Mantle

the rigid portion of Earth's mantle below the asthenosphere

high pressure

The lower mantle is rigid due to:

Buoyancy

the ability of an object to float in a fluid by displacement of a fluid equal to its mass

Isostatic Equilibrium

balanced support of lighter material in a heavier, displaced supporting matrix; analogous to buoyancy in a liquid

Isostatic Readjustment

the process where erosion of mountains causes uplift and deposition on the surrounding areas experiences subsidence

Fault

a fracture in a rock mass along which movement has occurred

Lord Kelvin

hypothesized that the Earth was around 80 million years old; theorized that as the Earth cooled, it shrunk and formed wrinkles - mountains

Radioactive Decay

the disintegration of unstable forms of elements, which releases subatomic particles and heat; contributes to Earth’s internal heat

Conduction

the transfer of heat through matter by the collision of one atom with another

Convection

movement within a fluid resulting from differential heating and cooling of the fluid; produces mass transport or mixing of the fluid

Uniformitarianism

the theory that all of Earth's geological features and history can be explained by processes occurring today and that these processes must have been at work for a very long time

James Hutton

developed his theory of uniformitarianism in 1788

Catastrophism

the theory that Earth's surface features are formed by catastrophic forces such as the biblical flood; belief in a young Earth and a literal interpretation of the biblical account of Creation

Leonardo da Vinci and Francis Bacon

noticed a certain correspondence between South America and Africa

Alfred Wegner

German meteorologist who proposed the theory of continental drift in 1912

Continental Drift

the theory that the continents move is across the surface of Earth

Pangea

name given by Alfred Wegner to the original “protocontinent”; the breakup of Pangea gave rise to the Atlantic Ocean and the modern continents

Panthalassa

name given by Alfred Wegener to the ocean sur rounding Pangaea

shoreline fit, Glossopteris distribution, glacial formations in the Southern hemisphere, existence of coal in Antarctica

Wegner’s evidence for continental drift:

centrifugal and tidal forces pulling the continents toward the equator

Wegner proposed that continental drift occurred because of:

Pacific Ring of Fire

the zone of seismic and volcanic activity that encircles the Pacific Ocean

Radiometric Dating

the process of determining the age of rocks by observing the ratio of unstable radioactive elements to stable decay products

young

Radiometric dating showed that oceanic crust was very _____ compared to continental crust:

Echo Sounders

a device that reflects sound off the ocean bottom to sense water depth. Its accuracy is affected by the variability of the speed of sound through water

Convection Current

a single closed-flow circuit of rising harm material and falling cool material

Seafloor Spreading

the theory that new ocean crust forms at spreading centers, most of which are on the ocean floor, and pushes the continents aside; power is thought to be provided convection currents in Earth's upper mantle

Harry Hess

proposed seafloor spreading in 1960

Spreading Center

the junction between diverging plates at which new ocean floor is being made; also called spreading zone

Subduction

the downward movement into the asthenosphere of a lithospheric plate

Subduction Zone

an area at which a lithospheric plate is descending into the asthenosphere. The zone is characterized by linear folds (trenches) in the ocean floor and strong deep-focus earthquakes; also called a Wadati-Benioff zone

Kiyoo Wadati and Hugo Benioff

speculated and charted on subduction and plate boundaries

Plate Tectonics

the theory that Earth's lithosphere is fractured into plates that move relative to each other and are driven by convection currents in the mantle; most volcanic and seismic activity occurs at plate margins

John Tuzo Wilson

Canadian geophysicist who proposed the theory of plate tectonics in 1965