Earth's Interior

Planetary Differentiation

The process by which the chemical elements of a planetary body accumulate heterogeneously throughout that body (occurred due to gravitational separation and/or chemical differentiation).

Goldschmidt Classification

Grouping scheme for chemical elements based on chemical attributes and behavior. Can be lithophile, siderophile, chalcophile, or atmophile elements.

Seismic Waves - Body

Similar to light and sound waves and can pass through the earth. Primary waves are faster but dependent on rock density and temperature. Secondary waves are more damaging, but slower and cannot travel through air or liquid.

Seismic Waves - Surface

Similar to ocean waves and are restricted to the surface of the earth. Slower, but more destructive.

Wave Reflection

Part of the wave energy bounces off boundaries.

Wave Refraction

The velocity (speed and direction) of the wave changes as it passes across boundaries.

Declination

The difference between the direction of magnetic north and true north for a particular place on earth.

Inclincation

A magnetic needle will also dip towards the earth as it aligns itself with the magnetic field.

Lithosphere

The relatively rigid, non-flowable, 100-150km thick layer of the earth (the crust and the top part of the mantle).

Asthenosphere

The relatively soft, 150 - 350km thick layer of the mantle. Can flow when acted on by a force.

The Moho

The boundary where a distinct change in velocity of seismic waves occurs as they pass through changing densities of rock.

Oceanic Crust

Generally mafic in composition (Fe and Mg rich), is comparably thin, dense, and young.

Continental Crust

Generally felsic in composition (Si and Al rich), is comparably thick, buoyant, and old.

Buoyancy

Upward force acting on an object immersed or floating in fluid.

Isostasy

The balance between buoyant (upward) and gravitational (downward) forces.

Geothermal Gradient

The increase in temperature with depth (expressed as C/km).

Crustal Heat

Radioactive decay of U, K, Th.

Mantle Heat

Heat from radioactive elements and core crystallization.