Glossary Starting with the letter: I

Ice Age

(glacial period, glacial epoch) Recurring periods in Earth’s history when the climate was colder and glaciers expanded to cover larger areas of the Earth’s surface. The most recent ice age occurred during the Pleistocene epoch.

Ice Core Samples

Samples of layered ice from glaciers which may contain dust, chemicals, and gases that have been deposited with snow over hundreds of thousands of years. These layers reveal past climate characteristics and many of their potential causes.

Ice Sheet

A large mass of ice thick enough to cover the topography under it. Ice sheets are large enough to deform and move with gravity.


Rock formed by solidification from a molten or partially molten state.


Any solid, liquid, or gaseous foreign substance trapped inside a mineral or rock. Also refers to a fragment of an older rock embedded within an igneous rock.


Electromagnetic radiation lying in the infrared spectrum with wavelengths greater than red light (longer than the longest visible wavelengths).

Inner Core

The central or innermost part of the Earth’s core, extending from a depth of 5,100 kilometers to the center of Earth at 6,400 kilometers. It is believed to be solid, as opposed to the outer core, which is liquid.


The solar radiation falling on Earth’s surface or its atmosphere. A contraction of “incoming solar radiation.”

Interdune Valleys

Valleys or depressions between sand dunes.


(interglacial period) The time between glaciations when Earth’s climate is warmer and the ice sheets have withdrawn, or retreated, from large areas of the continents. The present time is part of an interglacial period.

Intermediate Water

Layer of ocean water above the deep water and immediately below the mixed layer of water at the ocean surface.


A positively or negatively electronically-charged atom or molecule.

Island Arc

A curving group of volcanic islands parallel to a deep-sea trench. Island arcs and the deep-sea trench mark the location where oceanic crust is being subducted under oceanic crust. The Aleutian Islands are an island arc.


The mechanism whereby areas of the crust rise or subside until the mass of their topography is buoyantly supported or compensated by the thickness of crust below, which “floats” on the denser mantle below.


One or more atoms of the same chemical element that differ in atomic weight because they have different numbers of neutrons. The atomic weight of the isotope is written in superscript to the left of the chemical symbol, such as 14C.