Ice age

Ice age refers to a long-term period of reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers.

Definition

An Ice age is a period of long-term reduction in the temperature of Earth's surface and atmosphere, resulting in the expansion of continental ice sheets, alpine glaciers, and sea ice. An ice age may last several million years and drastically reshape the surface of the Earth through erosion and deposition of sediment.

Causes

The causes of ice ages are not fully understood for either the large-scale ice age periods or the smaller ebb and flow of glacial–interglacial periods within an ice age. The consensus is that several factors are important: atmospheric composition, such as the concentrations of carbon dioxide and methane, changes in the Earth's orbit around the Sun known as Milankovitch cycles, and the arrangement of continents as a result of plate tectonics.

Major Ice Ages

There have been at least five major ice ages in the Earth's past (the Huronian, Cryogenian, Andean-Saharan, Late Paleozoic, and the current Quaternary Ice Age). Outside these ages, the Earth seems to have been ice-free even in high latitudes.

Quaternary Ice Age

The current ice age, the Quaternary glaciation, began 2.58 million years ago in the late Pliocene, when the spread of ice sheets in the Northern Hemisphere began. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales called glacial periods, glacials or glacial advances, and interglacial periods, interglacials or glacial retreats.

Effects of Ice Ages

The effects of ice ages are profound. They have major impacts on the Earth's climate, atmosphere, and life forms. For instance, during an ice age, the sea level drops, creating land bridges between islands and continents, altering the habitat of many species and often leading to their migration.

See Also

• Glaciation
• Ice sheet
• Glacial period
• Interglacial period
• Quaternary glaciation