GeologyRocks

Ice Age

An extended period of time where there is extensive glaciation covering the Earth.

Inbreeding Coefficient (F)

The probability that an individual taken at random from the population will be autozygous.

Inbreeding Depression

Reduction, in inbred individuals, of the mean value of a character (usually one correlated with fitness).

Incompatible Elements

Incompatible relative to mantle minerals; those elements with large ionic radii such as Nb, Zr, U, Th, K, Na, Li, Be, REE, that preferentially go into the melt rather than remain in residual minerals.

Intrusion Magma

Magma that has crystallised beneath the surface.

Definition provided by: Tim Ivanic (University of Edinburgh)

Isolating Mechanism

A genetic difference between populations that prevents or restricts gene flow between them. See reproductive isolation.

Isostacy

The study of the responses of the Earth to loads (mountain belts, glaciers) placed on it. Isostatic theory states that at the depth of compensation all pressures exerted by rocks above are equal. Northern Europe is currently re-bounding from glaciers that were there during the Last Glacial Maximum, such that Scotland is raising and Kent is sinking.

Isostatic Sea Level Change

Sea level change on a local scale. Can be caused by glaciers making continents sink or melting glaciers making the continents rise again (isostatic rebound) or local tectonic activity. Combined with the eustatic changes make a relative sea level change.

Isotropic

An isotropic mineral appears opaque in thin section in polarised light.

Other meanings:

• Materials: In the study of mechanical properties of materials, "isotropic" means having identical values of a property in all crystallographic directions.

• Optics: Optical isotropy means having the same optical properties in all directions.