Plate Tectonics: A Scientific Revolution Unfolds

Practice vocabulary flashcards covering the historical development, plate boundary mechanisms, seafloor spreading evidence, and mantle convection models of plate tectonics.

Tectonic processes

Geologic processes that deform Earth's crust to create major structural features, including mountains, continents, and ocean basins.

Continental drift

A hypothesis championed by Alfred Wegener in 1915 suggesting that continents are not static but gradually migrate across the globe.

Pangaea

The single ancient supercontinent (meaning 'all lands') that existed about 200 million years ago before fragmenting into smaller continental blocks.

Edward Suess

An Austrian geologist (1831–1914) who pieced together early evidence for a past southern supercontinent called Gondwanaland, uniting South America, Africa, India, and Australia.

Sir Edward Bullard

A British scientist who, along with two associates in the early 1960s, constructed a map fitting the continental shelves of South America and Africa together at a depth of about 900 meters (3000 feet).

Oceanic ridge system

An interconnected, globally extensive mountain system that winds through all major ocean basins in a manner similar to the seams on a baseball.

Lithosphere

Earth's rigid outer mechanical layer composed of the entire crust and the uppermost mantle, averaging about 100 kilometers thick in the oceans and 150 to 200 kilometers or more beneath stable continental interiors.

Asthenosphere

The comparatively weak and hotter region in the upper mantle beneath the lithosphere where rock conditions are near their melting temperature, allowing flow.

Theory of plate tectonics

A comprehensive theory developed by 1968 that describes Earth's outer shell as consisting of individual moving lithospheric plates interacting along their margins.

Divergent plate boundaries

Constructive margins where two adjacent plates move apart from one another, producing long fractures where upwelling magma creates new seafloor.

Convergent plate boundaries

Destructive margins where two lithospheric plates move toward each other, causing the leading edge of one plate to descend into the mantle beneath the other.

Transform plate boundaries

Conservative margins where two plates grind horizontally past one another without creating or destroying lithospheric crust.

Spreading centers

Another name for divergent plate boundaries along the crests of oceanic ridges where adjacent plates spread apart and new ocean floor forms.

Subduction zones

Sites along convergent boundaries where older, cooler, and denser slabs of oceanic lithosphere sink downward into the asthenosphere and deeper mantle.

Deep-ocean trenches

Long, narrow, and exceptionally deep linear depressions on the seafloor created as oceanic lithosphere bends and descends into the mantle at subduction zones.

East African Rift

An active continental rift zone exhibiting tensional stretching, lithospheric thinning, and volcanic peaks such as Mount Kilimanjaro and Mount Kenya, representing the initial stage of continental breakup.

Trench migration

The gradual shift in geographic position of a subduction boundary over geologic time, such as the westward movement of the Peru-Chile trench caused by the westward drift of the South American plate.

Gulf of California

A long, narrow water body (also known as the Sea of Cortez) formed during the past 20 million years as the Baja California peninsula rifted away from mainland Mexico.

Breakup of Pangaea

The sequential rift-induced separation of the supercontinent Pangaea beginning between 180 and 165 million years ago with the opening of the North Atlantic.

Himalayas and Tibetan Highlands

Prominent mountain and plateau features formed approximately 50 million years ago when the northward-traveling Indian landmass collided with Eurasia.

Tethys Ocean

An ancient ocean that previously separated Africa from Eurasia, whose final remnant is the modern Mediterranean Sea.

Deep Sea Drilling Project

An oceanographic research project operating from 1968 to 1983 that extracted seafloor sediment and basalt cores, confirming that oceanic crust becomes progressively older away from ridge crests.

Paleomagnetism

The fossil magnetism preserved in iron-rich minerals within igneous rocks, recording the polarity and orientation of Earth's magnetic field at the time the rocks solidified.

Vine-Matthews hypothesis

A 1963 concept linking seafloor spreading with periodic geomagnetic reversals to explain alternating symmetric stripes of high- and low-intensity magnetism across mid-ocean ridges.

Whole-mantle model

A mantle convection model proposing that cold, descending oceanic slabs sink all the way to the core-mantle boundary while rising buoyant plumes transport hot material to the surface.

Layer cake model

A mantle convection model featuring two largely unmixed layers: an active upper convective zone driven by subducting slabs reaching no deeper than 1000 kilometers (620 miles), and a sluggish lower mantle that transfers heat upward.

Zubair Group

A collection of small volcanic islands off the western coast of Yemen in the southern Red Sea, near which a new volcanic island formed from 30-meter (100-foot) lava fountains in December 2011.