Layers of the Earth and Seismic Data

Flashcards covering the compositional and mechanical layers of the Earth, their physical properties, and the seismic evidence used to identify them.

Planetary Differentiation

The process during early heating where dense materials sank to the center and light materials rose to the surface, causing the Earth to divide into layers.

Compositional Layering

The classification of Earth's layers based on differences in chemical makeup and mineralogy, including the crust, mantle, and core.

Mechanical Layering

The classification of Earth's layers based on how materials deform and behave physically, including the lithosphere, asthenosphere, mesosphere, outer core, and inner core.

Crust

The thin, rigid, silicate-rich outermost layer of the Earth that is the site of earthquakes and volcanic activity.

Continental Crust

The granitic (silica and aluminum-rich) part of the crust that is $35-40\,km$ thick (up to $70\,km$ under mountains), less dense, and up to $4+$ billion years old.

Oceanic Crust

The basaltic (iron and magnesium-rich) part of the crust that is $5-10\,km$ thick, denser than continental crust, and less than $200$ million years old.

Mantle

The largest layer of Earth, composed of magnesium and iron-rich silicate minerals, which extends from the crust to the core and flows slowly to drive plate movement.

Core

The innermost region of Earth composed of metallic iron and nickel, serving as the source of heat for mantle convection.

Lithosphere

The rigid mechanical layer consisting of the crust and the uppermost mantle, ranging from $80-200\,km$ in thickness, which forms tectonic plates.

Asthenosphere

The ductile upper mantle layer at $80-250\,km$ depth that exhibits plastic flow and enables the movement of lithospheric plates.

Mesosphere

The solid and extremely strong mechanical layer corresponding to the lower mantle ($660-2900\,km$ depth) where high pressure creates denser mineral structures.

Outer Core

The liquid mechanical layer of the core that flows freely and generates Earth's magnetic field.

Inner Core

The solid mechanical layer at the center of the Earth where extreme pressure prevents the iron and nickel from melting.

Seismic Waves

Vibrations traveling through Earth from sources like earthquakes or volcanic eruptions, used as the primary tool for studying the interior.

P-waves

Primary or compressional waves that are the fastest seismic waves and can travel through solids, liquids, and gases.

S-waves

Shear waves that are slower than P-waves and can only travel through solid materials, not liquids or gases.

Seismic Shadow Zones

Regions where certain seismic waves never arrive from an earthquake, providing key evidence for Earth's layered interior.

S-wave Shadow Zone

A large area beyond a certain distance from an earthquake where no S-waves are detected, indicating the presence of a liquid outer core.

P-wave Shadow Zone

A region where P-waves arrive delayed or weakened because they refract sharply when entering the core.

Mohorovićić discontinuity

The boundary between the crust and the mantle where seismic wave speeds increase.

Core-mantle boundary

The internal boundary where P-waves slow down and S-waves vanish, identifying the start of the liquid outer core.

Inner-outer core boundary

The boundary where P-waves speed up again, indicating the transition from the liquid outer core to the solid inner core.