Layers of the Earth

Vocabulary flashcards covering Earth’s layers, seismic methods, discontinuities, and select contextual terms from the lecture notes.

Crust

The Earth’s thin, outermost solid layer where life exists.

Continental Crust

Thick, less-dense part of the crust composed mainly of granitic rocks; forms continents.

Oceanic Crust

Thin, dense part of the crust composed mainly of basaltic rocks; forms the ocean floors.

Mantle

Semi-solid layer beneath the crust that makes up about 80 % of Earth’s mass.

Outer Core

Liquid layer made of molten nickel and iron located beneath the mantle.

Inner Core

Solid, iron-rich center of the Earth found beneath the outer core.

Mohorovičić Discontinuity

Boundary between the crust and the mantle marked by a sudden increase in seismic wave velocity.

Gutenberg Discontinuity

Boundary between the mantle and the outer core where P-waves slow sharply and S-waves disappear.

Lehmann Discontinuity

Boundary between the liquid outer core and solid inner core indicated by renewed P-wave acceleration.

Seismic Waves

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

Body Waves

Seismic waves that travel through Earth’s interior (includes P and S waves).

Primary Waves (P-Waves)

Fast, compressional body waves that move through solids and liquids.

Secondary Waves (S-Waves)

Slower, shear body waves that move only through solids. Transverse waves that move up-and down. Travel 60-70 percent slower than P-waves

Surface Waves

Seismic waves that travel along Earth’s surface, causing most earthquake damage.

Seismograph

Complete instrument setup that detects and records seismic waves.

Seismometer

Sensitive sensor within a seismograph that measures ground motion.

Seismogram

Written or digital record produced by a seismograph showing seismic wave traces.

Wave Velocity Change

Increase or decrease in seismic speed that signals a transition between Earth layers.

Sound Waves

Mechanical waves used in ultrasound imaging; analogous to seismic waves in Earth studies.

Prenatal Ultrasound

Medical imaging technique using sound waves to visualize a fetus—illustrates wave-based probing like seismology.

Nickel and Iron

Dominant metal mixture forming both the liquid outer core and solid inner core.

Density

how compact or how loose the matter within an object is

Andrija Mohorovicic

Croatian seismologist behind the discovery of the Mohorovičić discontinuity, marking the boundary between the Earth's crust and mantle.

Beno Gutenberg

A German-American seismologist known for his research in earthquake mechanics and the Earth's interior structure. In honor of his contributions, the discontinuity between the mantle and the outer core is named after him.

Inge Lehmann

Danish seismologist who discovered the inner core of the Earth and developed the concept of a solid inner core separated from the outer core by the Lehmann discontinuity