D Double Prime
(D”)The name for the lowermost 100–200 kilometers of the mantle where physical and chemical properties change rapidly.
Debris Flow
The down-slope movement of a mass of unconsolidated rock, sand, and dirt, more than half of which is coarser than sand.
Decadal
On the time scale of decades, or tens of years.
Deep Water
The layer of the ocean between the intermediate water and the bottom water
Deglaciation
The uncovering of a landmass by retreat or melting of glacial ice.
Dendroclimatology
Measurement of time intervals by counting the annual rings of trees; applicable to the last 3,000–4,000 years.
Denudation
The progressive lowering of the Earth’s surface by erosion, weathering, mass wasting, and transportation.
Deposition
The act of laying down rock-forming matter (sediment) by a natural process, such as wind, water, or ice.
Deuterium
An isotope of hydrogen with one proton and one neutron in the nucleus, giving it an atomic weight of 2.
Differentiation
The process by which a magma changes composition, for example, by crystal fractionation. In reference to planets, the process of forming concentric layers of different composition, usually by sinking of dense material and floating of light material.
Dipole
Two poles of opposite charge but equal magnitude.
Discontinuity
A surface at which seismic wave velocities abruptly change due to changes in physical properties of the material the waves are traveling through (such as density or composition).