Plate Tectonics and Earth Structure Vocabulary

Vocabulary flashcards covering compositional and physical layers of the Earth, plate tectonics mechanisms, and plate boundary types.

Compositional Layers of the Earth

The four layers of Earth defined by chemistry and composition: Crust, Mantle, Outer Core, and Inner Core.

Crust

The thin outer compositional layer of Earth ($8\text{--}45\,\text{km}$ thick) composed of low-density elements including silicone, oxygen, and aluminum.

Continental Crust

A lower-density type of crust that forms landmasses and mountain ranges.

Oceanic Crust

A higher-density type of crust that forms the floor of the ocean.

Mantle (Compositional)

A thick compositional layer ($45\text{--}2900\,\text{km}$) containing denser elements rich in iron and magnesium that sank deeper during Earth's stratification.

Outer Core (Compositional)

The compositional layer of Earth where approximately $\frac{9}{10}$ of the composition consists of iron and nickel.

Inner Core (Compositional)

The innermost compositional layer consisting of $94\%$ iron, $5\%$ nickel, and $1\%$ other elements.

Physical Layers of the Earth

The five layers defined by physical and mechanical strength (how materials behave under force): Lithosphere, Asthenosphere, Lower Mantle (Mesosphere), Outer Core, and Inner Core.

Lithosphere

A brittle physical layer roughly $100\,\text{km}$ thick that includes the crust and uppermost solid mantle, which breaks when sufficient force is applied.

Asthenosphere

A hotter, ductile (plastic) physical layer of solid material beneath the lithosphere that bends, shifts, and oozes under force like peanut butter or play dough.

Lower Mantle (Mesosphere)

The physical layer of the mantle beneath the asthenosphere characterized by more brittle mechanical properties.

Outer Core (Physical)

The most ductile physical layer of the Earth, exhibiting mechanical behavior comparable to ketchup.

Inner Core (Physical)

The deepest physical layer of the Earth, which behaves as a brittle solid under mechanical stress.

Plate Tectonics Theory

The unifying geological theory developed in the 1960s stating that the lithosphere is divided into rigid pieces (plates) that move relative to one another.

Continental Drift Hypothesis

Alfred Wegener's hypothesis proposing that continents were once joined together based on matching features like mountain ranges, which lacked a mechanism to explain how continents move.

Mid Ocean Ridge (MOR)

An underwater mountain range mapped during the 1940s and 1950s where young seafloor rocks form, accompanied by volcanism and small-to-medium earthquakes.

Seafloor Spreading

The process where rising magma creates new rock along a mid-ocean ridge, pushing the seafloor apart and moving continental plates on either side.

Magnetic Reversals

Historical polarity flips of Earth's magnetic field preserved in seafloor rocks, showing alternating bands pointing North (grey) or South (white).

Mantle Convection

A mechanism driving plate movement where mantle material heats up, becomes less dense and rises, then cools near the surface, increases in density, and sinks.

Ridge Push

A plate movement mechanism where buoyant magma pushing up at the mid-ocean ridge physically forces tectonic plates apart.

Slab Pull Model

A mechanism of plate motion where an old, dense, heavy oceanic plate sinks into the subduction zone, pulling the rest of the plate behind it like a conveyor belt.

Slab Suction

A process where a subducting rock slab drags down surrounding asthenospheric material due to high friction, helping to sustain the mantle convection cell.

Divergent Margins

Plate boundaries where tectonic plates pull away from a central rift zone, creating features such as Mid Ocean Ridges and continental Rift Valleys.

Rift Valleys

Divergent boundaries situated within a continent (such as the East African Rift Zone) that can either stop spreading or open wide enough to create a new ocean basin.

Convergent Margins

Plate boundaries where tectonic plates collide or move toward each other, forming Subduction Zones or Continental Collision Zones.

Subduction Zone

A convergent boundary where denser oceanic lithosphere sinks beneath continental lithosphere, triggering onshore volcanic arcs and severe earthquakes (e.g., along the West Coast of South America).

Continental Collision Zone

A convergent boundary where two continental plates collide, pushing rock layers upward to form mountain chains (e.g., the Appalachian Mountains) without volcanic activity.

Transform Margins

Plate boundaries where two tectonic plates slide past each other horizontally, producing substantial earthquake activity (e.g., San Andreas Fault in California).

Tectonic Plates

Major structural slabs of Earth's lithosphere, including the Nazca, North American, South American, Eurasian, and Pacific plates.