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Causes of Glaciation

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  • 0:02 Glaciation
  • 0:32 Ice Age
  • 1:05 Continental Positions
  • 1:55 Milankovitch Theory
  • 4:31 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Glaciation refers to being covered with glaciers. Learn about the theories behind glaciation, including the changing continental positions and the Milankovitch theory, which points to three orbital variations: eccentricity, obliquity and precession, in this lesson.

Glaciation

Earth is a dynamic place with major changes happening constantly, changes so big that we cannot perceive them: the Earth turns on its axis, continents shift their positions and glaciers grow and recede all beyond our conscious awareness. In this lesson, we will explore how the constant moving of the continents and cyclic changes in the Earth's orbit result in periods of glaciation, where we see the covering of large areas with glaciers.

Ice Age

You have probably heard the term ice age, which, simply put, is a long period of cold temperatures. And when I say long, I mean long - as in millions of years. Yet, within an ice age there are episodes of fairly extensive glaciation, where we see glaciers growing and advancing, broken up by episodes of relatively warm temperatures when glaciers retreat. Geologists believe Earth has survived through five major ice ages in the past 2.4 billion years. So, what causes the Earth to periodically freeze up?

Changing Continental Positions

Well, there are two main theories behind the cause of glaciation. One theory has to do with changing continental positions, which is based on the theory of plate tectonics, in which scientists believe that the Earth's surface is made up of large plates that move over top of a more fluid, deeper layer (somewhat like how a puck glides over an air hockey table). The continents sit on top of these large plates and therefore their positions are constantly changing.

This movement of large land masses affects the circulation patterns of the oceans and atmosphere. When these circulation patterns change, the result is a change in climate. For example, if continents shift in such a way that they block warm water currents from the equator from making their way north to the poles, then ice can grow in those polar regions.

The Milankovitch Theory

Another theory to explain the cause of glaciation is the variations in the Earth's orbit that occur in cyclic fashions. This theory, known as the Milankovitch theory after the man credited with its development, points to three orbital variations that result in the long-term climate change needed for glaciation.

The first is eccentricity, which is defined as changes in the Earth's orbit around the sun. The Earth can follow a nice even circular path around the sun, or it can follow a more oblong path. When the Earth follows this oblong path, we could say that the orbit is a bit off, just like a person who is eccentric could be said to be a bit off. This change in the Earth's orbit does not happen suddenly; it takes about 100,000 years to go from circular to eccentric and back. But when the Earth is in the farthest position of the oblong orbit, the Earth and the sun are far apart. This lessens the amount of warm sunlight hitting the Earth, which promotes glaciation.

The second orbital variation to consider is obliquity, which is defined as shifts in the tilt of the Earth's axis. It might help you to recall this term if you remember that when something is oblique it's slanted, so obliquity is describing how much the Earth is slanted. This slant, or tilt, varies only a couple of degrees, from 22.1 degrees to 24.5 degrees. Yet, this small change takes about 41,000 years to complete, and is enough to influence the intensity of the seasons. For example, less tilt means fewer extremes, so there is less cold in the winter and less heat in the summer. These cooler summer months allow the snow that falls over the winter to stick around. Over years, this snow builds up and glaciers are born.

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