Earth's Interior & Plate Tectonics

Vocabulary flashcards covering key terms from the chapter on Earth’s Interior and Plate Tectonics.

Crust

Earth’s outermost solid layer composed of hard rock and soil.

Oceanic crust

5–10 km-thick basaltic crust beneath oceans; dense (~3.0 g/cm³) and generally <200 million years old.

Continental crust

10–70 km-thick granitic crust forming continents; less dense (~2.7 g/cm³) and up to 3.8 billion years old.

Mantle

About 2,885 km-thick layer beneath the crust; solid but plastic-behaving rock divided into upper and lower parts.

Lithosphere

Rigid outer shell consisting of the crust plus the uppermost solid mantle.

Asthenosphere

Hot, weak, partially molten zone (≈100–250 km deep) beneath the lithosphere where convection occurs.

Core

Central metallic part of Earth, mostly iron-nickel, divided into a liquid outer core and a solid inner core.

Outer core

≈2,210 km-thick liquid iron-nickel layer with temperatures about 3,000–6,500 °C.

Inner core

≈1,216 km-thick solid iron-nickel sphere reaching ~7,000 °C.

Convection current

Circular flow of mantle material caused by differential heating, driving plate motion.

Convection cell

Single loop of rising hot mantle, lateral flow, cooling, and sinking dense material.

Tectonic plate

Large, rigid slab of lithosphere that floats on the asthenosphere and moves independently.

Plate tectonics theory

Unifying model explaining formation, movement and interaction of lithospheric plates at Earth’s surface.

Continental drift theory

Wegener’s hypothesis that continents were once joined in Pangaea and have since drifted apart.

Pangaea

Supercontinent that existed roughly 300 million years ago before breaking into today’s continents.

Seafloor spreading

Hess’s idea that new oceanic crust forms at mid-ocean ridges and moves outward, widening the ocean floor.

Mid-ocean ridge

Long, continuous mountain chain on the ocean floor where magma rises and new crust is created.

Rift valley

Central crack or depression along a mid-ocean ridge where the seafloor splits.

Subduction zone

Region where one tectonic plate is forced beneath another into the mantle.

Trench

Deep, narrow depression on the ocean floor formed at a subduction zone.

Island arc

Curved chain of volcanic islands that forms above an oceanic-oceanic subduction zone.

Volcanic arc

Line of volcanoes on a continent above an oceanic-continental subduction zone.

Convergent boundary

Plate boundary where two plates move toward each other, causing subduction or collision.

Divergent boundary

Plate boundary where two plates move apart and new lithosphere forms from rising magma.

Transform boundary

Plate boundary where two plates slide horizontally past one another, producing faults and earthquakes.

Hot spot

Fixed area of mantle melting where magma pierces a moving plate, forming volcanic chains like Hawaii.

Mountain range

Elevated region primarily produced by continental-continental collision and crustal compression.

Ring of Fire

Seismically active belt of volcanoes and earthquakes encircling the Pacific Ocean, linked to subduction.

Circum-Pacific Belt

Alternate name for the Ring of Fire seismic and volcanic zone.

Alpine-Himalayan Belt

Major seismic belt running through the Mediterranean, Middle East, and Himalayas.

Radioactive decay

Breakdown of unstable isotopes (e.g., uranium, thorium) that releases heat within Earth.

Seismic waves

Energy waves generated by earthquakes that travel through Earth’s interior.

Seismogram

Recorded trace of seismic waves used to analyze Earth’s internal structure.

Remote sensing

Collecting information about Earth using electromagnetic radiation detected by satellites or aircraft.

Global Positioning System (GPS)

Satellite-based technology that precisely measures locations and tracks plate motions.

Oceanic-oceanic convergence

Meeting of two oceanic plates where the denser plate subducts, forming trenches and island arcs.

Oceanic-continental convergence

Collision of an oceanic plate with a continental plate, producing subduction zones and volcanic arcs.

Continental-continental convergence

Collision of two continental plates that thickens crust and builds high mountain ranges.

Subduction

Process by which one tectonic plate is forced downward into the mantle beneath another plate.

Fault

Fracture in Earth’s crust along which movement has occurred, often producing earthquakes.