Plate Tectonics and Earth's Structure

Vocabulary practice flashcards covering Earth's internal layers, plate boundary types, continental drift evidence, and tectonic processes.

Endogenic Forces

Forces originating from within the Earth that move the crust vertically and horizontally, caused by convection currents.

Inner Core

A solid, $1{,}220\,\text{km}$ thick layer under high pressure composed of iron and nickel at $6000^\circ\text{C}$ that transfers heat.

Outer Core

A $2{,}220\,\text{km}$ thick molten layer under less pressure composed of iron and nickel that spins around the inner core to generate Earth's magnetic field.

Lower Mantle

The lowest, mainly solid section of the mantle where convection currents begin and columns of molten magma rise toward the crust.

Asthenosphere

A $100\text{--}200\,\text{km}$ thick elastic mantle layer where magma columns become semi-molten and tectonic plates slide on top.

Plasticity

The slow, flowing movement characteristic of semi-molten magma.

Lithosphere

The $50\text{--}100\,\text{km}$ thick, solid, rigid, and brittle outer layer composed of the upper mantle and crust combined, which is divided into tectonic plates.

Moho (Mohorovičić Discontinuity)

The boundary where the solid upper mantle meets the Earth's crust.

Continental Crust (SIAL)

Thick crust averaging $45\,\text{km}$ (thinning to $30\,\text{km}$ where pulled apart) composed of light granite rock rich in silica and aluminum.

Oceanic Crust (SIMA)

Thin crust averaging $8\,\text{km}$ (thinning to $3\,\text{km}$ at mid-ocean ridges) composed of heavy basalt rock rich in silica and magnesium.

Gutenburg Discontinuity

The boundary that separates the Earth's mantle from the core.

Plate Tectonics

The theory explaining Earth's structure and the movement of lithospheric plates at approximately $1\,\text{cm}$ per year under the influence of endogenic forces.

Continental Drift

The theory proposed by Alfred Wegner (Wegener) that a supercontinent called Pangaea split $200\,\text{mya}$ into two continents and continued splitting over time.

Continental Fit

The jigsaw-like alignment of continental coastlines, such as the fitting together of South America and Africa.

Mesosaurus

A freshwater reptile fossil discovered on separate continents across the Atlantic, used as fossil evidence that the continents were once joined.

Glossopteris

A fossil plant found across Africa, Australia, and Antarctica that provides evidence for continental drift.

Convection Currents (Arthur Holmes)

A process explaining plate movement driven by columns of magma rising from the lower mantle to the upper mantle.

Ridge Push

The tectonic process that drives and explains how plates separate from each other at mid-ocean ridges.

Subduction and Slab Pull

The process where a heavier oceanic plate sinks into the asthenosphere (melting at $100\,\text{km}$ depth) and drags the rest of the plate along with it.

Seafloor Spreading (Harry Hess)

The discovery that new basaltic ocean floor continuously forms at mid-ocean ridges as magma rises and cools in seawater.

Geomagnetic Striping (Drummond Mathews and Frederick Vine)

Proof of seafloor spreading shown by iron filings in cooling basalt recording reversals in Earth's magnetic polarity every $100{,}000$ years.

Constructive (Divergent) Boundary

A boundary where two plates move apart due to rising convection currents, resulting in features such as mid-ocean ridges and rift valleys.

Rifting

The process where diverging convection currents stretch and thin continental crust, forming a valley floor with volcanoes that may drop below sea level and flood.

East African Rift Valley

A continental rift valley featuring volcanoes such as Mt Kilimanjaro, where northern crust has dropped below sea level to allow the Indian Ocean to flood in and form the Red Sea.

Mid-Atlantic Ridge

A constructive boundary separating the North American and Eurasian plates at roughly $2.5\,\text{cm}$ per year; formed the Atlantic Ocean $130\,\text{mya}$ and volcanic islands such as Iceland ($16\text{--}18\,\text{mya}$).

Destructive (Convergent) Boundary

A plate boundary where two tectonic plates move toward one another and collide.

Oceanic-to-Oceanic Collision

A convergent collision where the denser oceanic plate subducts and melts at $200\,\text{km}$ depth, creating deep ocean trenches (e.g., Mariana Trench) and volcanic island arcs (e.g., Philippine Islands).

Oceanic-to-Continental Collision

A convergent collision where dense oceanic crust subducts under continental crust, producing deep trenches, explosive eruptions from thick silica-rich magma, and fold mountains such as the Andes.

Continental-to-Continental Collision

A collision between two buoyant continental plates where neither subducts, causing crustal compression that buckles upward into fold mountains like the Himalayas.

Transform (Passive) Boundary

A boundary where two plates slide past each other horizontally without creating or destroying land, locking together until stored pressure releases suddenly as earthquakes.

San Andreas Fault

A transform fault in California where the Pacific Plate moves northwest faster than the North American Plate due to slab pull under Alaska, with the North American plate acting like a brake.