Lecture 3 09/05/25 Earth's interior

Vocabulary flashcards covering Earth's internal structure, seismic waves, mantle convection, core properties, and related evidence.

Crust

Earth’s outermost solid shell, consisting of oceanic crust (basalt; ~7–10 km thick) and continental crust (granite; ~35–40 km thick).

Oceanic crust

Thin, dense crust composed mainly of basalt; thickness ~7–10 km; density ~3 g/cm³.

Continental crust

Thicker, less dense crust composed mainly of granitic rocks; thickness ~35–40 km (up to >70 km in mountains); density ~2.7 g/cm³.

Mantle

Layer between crust and core; ~2,885 km thick; makes up ~82% of Earth's volume; composed mainly of ultramafic rock called peridotite; convects slowly.

Peridotite

Ultramafic mantle rock that is the primary composition of the Earth's mantle.

Lithosphere

Rigid outer shell consisting of the crust plus the uppermost mantle (above ~100–150 km depth).

Asthenosphere

Mantle below the lithosphere that is hot and ductile, allowing flow on long timescales.

Deep Mantle

Lower portion of the mantle that remains solid but deforms slowly (ductile behavior).

Outer core

Liquid iron–nickel alloy region, ~2,255 km thick; density ~10–12 g/cm³; convection here generates Earth's magnetic field.

Inner core

Solid sphere at Earth's center, radius ~1,220 km; density ~13 g/cm³; extremely high temperature and pressure.

Core

Center region of Earth consisting of a liquid outer core and a solid inner core.

Core composition

Predominantly iron–nickel alloy with minor oxygen, silicon, and sulfur.

Mantle convection

Slow circulation within the mantle where hot material rises and cool material sinks, driving plate tectonics.

Seismic waves

Energy waves produced by earthquakes that travel through Earth; speeds reveal layer properties and boundaries.

P-waves (Primary waves)

Compressional body waves; fastest seismic waves; motion in the direction of travel; can travel through solids and liquids.

S-waves (Secondary waves)

Shear body waves; motion perpendicular to travel direction; cannot travel through liquids; slower than P-waves.

Shadow zones

Areas where seismic waves are not detected due to refraction or inability to pass through certain layers (e.g., S-waves cannot travel through the liquid outer core; P-waves have a detectable shadow between ~103°–150°).

Seismograph

Instrument that records seismic waves on a plot of ground motion.

Seismology

Study of Earth's interior and structure through seismic waves.

Geodynamo

Process by which convection in the liquid outer core generates electric currents, producing Earth’s magnetic field.

Magnetic field

Earth’s magnetic field, approximated as a dipole, generated by the geodynamo.

Paleomagnetism

Study of the ancient magnetic field recorded in rocks.

Thermoremanent magnetization

Magnetization in rocks locked in as they cool, preserving past magnetic conditions.

Depositional remanent magnetization

Magnetization preserved when rocks are deposited, reflecting past magnetic fields.

Magnetic pole reversals

Flip of the Earth's magnetic north and south poles; recorded in rocks, leading to the paleomagnetic time scale.

Cretaceous quiet zone

Period of predominantly normal polarity in the rock record during the Cretaceous.

Basalt

Dark, fine-grained igneous rock; principal component of oceanic crust.

Granite

Light-colored, coarse-grained igneous rock; principal component of continental crust.

Xenolith

Fragment of mantle rock brought to the surface by magma, providing mantle samples.

Meteorites (types)

Sources of evidence for Earth's composition: iron meteorites (core), stony meteorites (mantle), and stony-iron meteorites (mantle+core).