Vertical distance above sea level.




Pertaining to the north polar region.


Fragments of volcanic rock less than 2 mm in diameter.


The envelope of gases surrounding a planet, e.g., Earthàs atmosphere consists of approximately 80 percent nitrogen and 20 percent oxygen.


The smallest individual particle that retains the distinctive properties of a given chemical element.

axis of rotation

The imaginary line around which an object rotates.


The continuous mass of solid rock that makes up Earthàs crust.


The totality of living things on Earth, along with their habitats.

carbon dating

A method of determining the approximate age in years of a carbon-bearing object by measuring the decay of radioactive carbon-14.

Carbon dioxide

A molecule consisting of one carbon atom and two oxygen atoms (CO2). Its gas is denser than air.

Circum-Antarctic Current

The surface oceanic current encircling Antarctica that flows from west to east. Also called Circumpolar Antarctic Current or West Wind Drift.


Average weather conditions of a region, including temperature, precipitation, and winds.dataInformation, often in the form of measurements or observations, which can be analyzed.


The average mass per unit volume of a substance.


An interval of geologic time; a subdivision of a geologic period.

Equatorial Countercurrent

A band of eastward flow between the westward flowing North and South Equatorial Currents. Also called North Equatorial Countercurrent.

glacial lake

A lake formed by the melting of glacier ice.


The formation, advance, and retreat of glaciers through time. Glaciation of a region refers to the accumulation of ice over that region.


A permanent body of ice that shows evidence of downslope or outward movement due to the stress of its own weight.


The study of glaciers.

global warming

An increase in Earth's average temperature.

greenhouse gases

Gases, primarily water vapor, carbon dioxide, ozone, nitrous oxide, and methane, which increase global temperatures by absorbing outgoing radiation emitted by the Earth's surface. Also called GHGs.

Gulf Stream

A warm ocean current of the northern Atlantic Ocean off eastern North America. It originates in the Gulf of Mexico, then flows northward along the southeast coast of the US. North of Cape Hatteras, NC, the Gulf Stream veers northeastward into the Atlantic Ocean.


The geologic epoch extending from the end of the last glaciation, 10,000 years ago, to the present.


The total amount of water on Earth. It includes oceans, lakes, rivers, underground water, and all the snow and ice, including glaciers.

ice age

A cycle of advance and retreat of large continental ice sheets. Also refers to a much longer interval of geologic time during which extensive ice sheets formed and retreated repeatedly over many parts of the world, e.g., the Pleistocene epoch.

ice cap

A sheet of glacier ice and snow that covers a mountain highland and flows radially.

ice core

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

ice floe

A flat, free-floating chunk of ice broken from the frozen surface of a river, lake, or sheetA continent-sized mass of glacier ice that overwhelms the underlying topography.

ice shelf

Thick glacier ice that extends from glaciers on land and floats on the sea. Often called an ice tongue when it extends from the mouth of an outlet glacier.

ice tongue

See ice shelf.


A massive chunk of glacier ice floating in water or stranded on a shore.


Invisible electromagnetic radiation (light) with wavelengths longer than red light and shorter than microwaves. Infrared light occupies the spectral band extending from 0.75 to about 200 micrometers.


A period of warmth separating two major glacial periods.


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.

kilometer (abbreviated km)

A unit of length equal to 1,000 meters, or 0.62 miles.


Imaginary lines that allow measurement of position north or south of the equator (ìhorizontalî). Latitude is measured in degrees (at the equator one degree = 60 nautical miles, or 111 kilometers). The equator is at a latitude of 0° and the poles lie at latitudes of 90° north (North Pole) or 90° south (South Pole). Because of Earth's oblateness, a degree latitude near the polar regions is about 112 km in length.


A unit of length in the metric system equal to 3.28 feet.


An odorless, colorless, flammable gas (CH4). Methane is the principal constituent of natural gas.

Milankovitch cycles

Cycles of change in the path of Earthàs orbit around the sun, the tilt of Earthàs axis, and Earthàs rotation around that axis. Milankovitch cycles appear to influence the timing of when large continental ice sheets advance and retreat on Earth.


A theoretical system that represents scientific processes using a set of variables and the quantitative relationships between them.


An accumulation of poorly sorted glacial sediments deposited beneath or at the margin of a glacier and having a surface form that is unrelated to the underlying bedrock.


An electrically neutral subatomic particle found in the nucleus of all atoms except the lightest isotope of hydrogen.

North Atlantic

The northern part of the Atlantic Ocean, extending northward from about eight degrees north latitude to the Arctic Ocean. The North Atlantic is separated from the South Atlantic by equatorial countercurrents at about eight degrees north.

Northern Hemisphere

The half of Earth north of the equator.


The path of one celestial body moving around another under the force of gravity.

outlet glacier

A stream of glacier ice flowing rapidly from a larger body of glacier ice such as an ice sheet or ice cap.


An element consisting of atoms with eight protons. Two oxygen atoms combine to make molecular oxygen (O2) and three make ozone (O3). Earth's atmosphere is 20 percent molecular oxygen.


Past climate.

period, geologic

An interval of geologic time; a subdivision of a geologic era.


Permanently frozen soil or subsoil, occurring throughout the polar regions and locally in perennially frigid areas.


The geologic epoch lasting from 1,800,000 years ago to 10,000 years ago.


Relating to or located near the North Pole or South Pole.


The transfer of moisture from the atmosphere to the surface of Earth, usually as rain, snow, and ice.


A thing that yields clues to environmental conditions of the past.


The emission of energy by waves (including light) or particles.

sea ice

Frozen seawater that floats on the oceanàs surface.


Unconsolidated particles, ranging from clay-size to boulders, produced by the breakdown of rocks that may be carried by natural agents (wind, water, and ice), and eventually deposited to form sedimentary deposits. Organisms and chemical precipitation can also produce sediment.


A representation, often mathematical or visual, of the behavior of a system over time.

Southern Hemisphere

The half of Earth south of the equator.

stratum (pl. strata)

A distinct layer of sediment that accumulated at Earthàs surface.terminusThe outer, lower margin of a glacier.


The surface elevation of land and its variations.


Existing between 23° north and 23° south of the equator.


A vent or fissure in the Earth's surface through which molten lava, ash, and gases are ejected. It is also the name for the structure, usually conical, formed by the materials ejected from the vent or fissure.


The state of the atmosphere at a specific time and place. Weather is reflected by variables of temperature, moisture, wind velocity, and barometric pressure.

Younger Dryas

A period of abrupt climate change during the Pleistocene Epoch. During this time, temperatures on Earth rapidly dropped around 12,900 years ago, then rapidly resumed to near pre-Younger Dryas levels about 11,600 years ago.