Pointers in Science - Plate Tectonics and Earth's Interior

A set of vocabulary-style flashcards covering plate boundaries, Earth's interior structure, seismic waves, continental drift, and related concepts from the notes.

Plate boundary

The edge where two tectonic plates meet; interactions at plate boundaries shape mountains, earthquakes, and volcanoes.

Convergent boundary

A boundary where plates move toward each other; can form mountains or trigger subduction and volcanism.

Divergent boundary

A boundary where plates move apart; causes seafloor spreading and formation of new crust at mid-ocean ridges.

Transform-fault boundary

A boundary where plates slide horizontally past one another; earthquakes are common with little volcanism.

Mid-ocean ridge

An underwater mountain range formed at divergent boundaries where new oceanic crust is created.

Pacific Ring of Fire

A ring around the Pacific Ocean with frequent earthquakes and volcanoes due to plate interactions.

Hotspot

A fixed mantle plume that creates volcanic activity as a tectonic plate moves over it.

Subduction

The process of one plate sinking beneath another at a convergent boundary, leading to deep earthquakes and volcanism.

Continental drift theory

The hypothesis that continents move slowly over Earth's surface; proposed by Alfred Wegener.

Proponent of Continental Drift Theory

Alfred Wegener, who proposed that continents were once joined and drifted apart.

Pangaea

A supercontinent that existed about 300 million years ago from which current continents separated.

Fossils supporting continental drift

Similar fossils on now-separated continents (e.g., Mesosaurus, Glossopteris) indicating past connections.

Evidence for Continental Drift

Matching coastlines, fossil distribution, rock formations, and climatic clues indicating continental movement.

Oceanic crust

Thinner, more dense crust composed mainly of basalt.

Continental crust

Thicker, less dense crust composed mainly of granitic rocks.

Lithosphere

Rigid outer layer of Earth including the crust and upper mantle.

Outer core

Liquid layer beneath the mantle, primarily iron and nickel; generates Earth's magnetic field.

Inner core

Solid sphere at Earth's center, mainly iron-nickel alloy.

Seismic waves

Waves of energy from earthquakes; include P-waves, S-waves, and surface waves.

P-waves

Primary seismic waves that compress and expand the ground; the fastest waves.

S-waves

Secondary seismic waves that shear ground motion; cannot travel through liquids.

Epicenter

Point on Earth's surface directly above the earthquake's focus.

Focus (hypocenter)

The point within Earth where an earthquake originates.

Convection current

Circular movement of mantle material that drives mantle heat transfer and plate motion.

Crustal composition and density

Oceanic crust is thinner and more dense (basaltic) than continental crust (granitic).

Why is the outer core liquid?

S-waves cannot travel through liquids; the absence of S-waves in certain zones indicates a liquid outer core.

Why epicenter is important

Identifies where shaking is strongest on the surface to aid hazard assessment and response.

Gondwana

Ancient supercontinent that included Antarctica, Africa, South America, Australia, and India.

Why Earth’s width does not increase

Crust is recycled by subduction; new crust forms at ridges while old crust subducts, keeping Earth's size roughly constant.

Location of Antarctica before

Antarctica was part of Gondwana, positioned near Africa, Australia, and South America before breakup.

Locations of volcanoes, mountains and epicenters

Concentrated along plate boundaries and activity belts such as the circum-Pacific Ring of Fire and mid-ocean ridges.