Earth Science: Earth's Interior, Seismic Waves, and Plate Tectonics

Vocabulary flashcards reviewing Earth structure, seismic wave dynamics, continental drift theory, and seafloor spreading.

Andrija Mohorovicic

A geophysicist from Croatia who discovered that the velocity of seismic waves increases abruptly below $50\,\text{km}$ depth.

Mohorovicic Discontinuity (Moho)

The boundary interface separating the Earth's crust and mantle.

Mantle

The thickest layer of the Earth, located beneath the crust at $2900\,\text{km}$ from the surface, consisting of solid rock that exhibits plasticity to flow.

Mantle Convection Currents

The thermal process where hot magma in the mantle rises to the top, cools, sinks, reheats, and rises again, driving changes on Earth's surface.

Beno Gutenberg

A German seismologist who observed that P waves diminish and die out at about $105^\circ$, and reappearing about $140^\circ$ away from an epicenter.

Shadow Zone

A $35^\circ$ wide belt around Earth where direct P waves are absent.

Gutenberg Discontinuity

The boundary marking the interface between the mantle and outer core.

Core

The innermost layer of Earth composed of a nickel and iron alloy, representing $16\%$ of Earth's volume, located $1,800\,\text{miles}$ beneath the crust and about $1,400\,\text{miles}$ thick.

Outer Core

A liquid layer of molten metal at about $3000^\circ\text{C}$ with a thickness of $2270\,\text{km}$, where convection flow of metallic iron generates Earth's magnetic field.

Inner Core

A solid sphere composed of iron kept solid by compression from outer layers, with heat generated by radioactive decay of elements like uranium and temperatures reaching up to $6,650^\circ\text{C}$.

Earth's Layers Diagram

Diagram showing Earth's structural divisions (Crust, Upper Mantle, Lower Mantle, Outer Core, Inner Core) and boundary discontinuities (Mohorovičić, Gutenberg, Lehman).

Inge Lehmann

A Danish seismologist who discovered the solid inner core within the molten outer core.

Lehmann Discontinuity

The interface between the liquid outer core and the solid inner core.

Seismic Waves

Waves of energy caused by the sudden breaking of rocks within the Earth or an explosion, which travel through the Earth and are recorded on seismographs.

Primary or P Waves (Compression Waves)

The fastest kind of seismic wave that moves through solid rock and fluids by pushing and pulling rock.

Secondary or S Waves (Transverse Waves)

The second seismic wave felt after an earthquake, slower than P waves, which moves rock up and down or side to side and can only travel through solid rocks.

Love Waves

The fastest surface wave, modeled mathematically by Augustus Edward Hough Love in $1911$, which moves the ground from side to side.

Rayleigh Waves

A surface wave predicted mathematically by Lord Rayleigh in $1885$ that rolls along the ground, moving it up, down, and side to side in the direction of wave travel, causing most earthquake shaking.

Alfred L. Wegener

Geologist who observed matching rocks and fossil remains across continents, proposed the Continental Drift Theory, named the supercontinent Pangea, and published his first version in $1912$.

Pangea

The single "SUPER" continent proposed in the Continental Drift Theory before its landmasses separated.

Antonio Pellegrini

An individual who depicted in $1858$ that Africa and South America were once connected and published maps demonstrating this.

Seafloor Spreading Theory

Theory studied in $1963$ by Robert Diaz and Harry Hess using SONAR, proposing that continental movement is caused by ocean floor movement.

SONAR

Sound wave technology used by Robert Diaz and Harry Hess in $1963$ to study and map the ocean floor.

Evidences for Seafloor Spreading

Key findings supporting seafloor spreading including age of rocks (younger rocks and thinner sediments at mid-ocean ridges) and magnetic stripes.