http://museum.state.il.us/exhibits/ice_ages

http://www.pbs.org/wgbh/nova/ice/chill/html

www.pbs.org/wgbh/nova/ice/chill.html

http://www.dkrz.de/dkrz/broschuere-eng/research/iceage.html

LINKS TO OTHER SITES

http://www.pbs.org/wgbh/nova/ice/chill.htm

http://www.dmns.org/iceage/index.htm

http://dept.kent.edu/geology/sclement/history/casestudy

/pleistocene/pleistocene_files/frame.htm

http://adamite.igs.indiana.edu/indgeol/time/ Frzframe.htm

http://culter.colorado.edu:1030/~saelias/glacier.html

http://pubs.usgs.gov/gip/ice_age

ttp://museum.state.il.us/exhibits/ice_ages

http://www.dkrz.de/dkrz/broschuere-eng/research/iceage.html

http://adamite.igs.indiana.edu/indgeol/time/ Frzframe.htm

Ice Age: 101

Introduction

The reoccurring patterns of glacier formation, progression and recession followed by a period of global warming are the tradmark events which signify an ice age (Ray,1999). The most recent of these cycles of advancing and retreating ice sheets has been occurring for the last 2.5 million years specifically across North America and Eurasia, but remenants of glaciers have been found on all the major continents of the world (Denver Museum of Nature and Science, 2002).

Physically, ice ages are made up of glaciers which form due to long periods of cool climates which allow for snow fall to build up and compact year after year. Eventually, the weight of the compacted snow and ice forms glaciers, or sheets of ice, that migrate southward as a result of their weight (Geobopological Survey, 2000).

Geologic Processes

Plate tectonics is the main geological process that perpetuates the climate changes necessary for ice ages to occur (Maasch, 1997). By shifting the positions of North America, Eurasia, and Antarctica from low latitudes to high latitidues, ice sheets were able to form in climates that were originally much warmer (Illinois State Museum, 2002). Plate movements can also cause uplifts in the continental crust which in turn can cause drastic changes in weather patterns (Illinois State Museum, 2002). Because the continental crust has risen over 600 meters in the last 15 million years, circulation patterns have been influenced by high atmospheric currents resulting in a decrease in climate temperatures (Illinois State Museum, 2002).

www.pbs.org/wgbh/nova/ice/chill.html

The cyclic nature of ice ages which is characterized by a long period of climate cooling followed by a relatively short period of climate warming, is explanded by the flucuation of solar energy radiated by the Sun. Because the Earth's axis is tilted at a 235 degree angle, the amount of sunlight hitting the Earth varies at different parts of the globe. The cycle of the Earth from left of center to right of center due to the axis tilt takes 41,000 years. At one extreme of this cycle, the southern hemisphere of the Earth is at its closest position to the Sun while the northern hemisphere is at it farthest, and at the other extreme of the cycle this phenomenon is reversed. Thus the axis angle of the Earth is directly related to the over all climate of the Earth which in turn affects the formation of glaciers (Elias, 2002).

Products of the Geologic Process

Temperature variation, which is caused by the movement of continental positions to high latitudes and the upwhelding of contiental crust, created global temperatures that were coolier than those of the present climate by 6 to 12 degress Celsius. This allowed for the build up of glaciers to occur in large regions of northern and eatern Canada which remained frozen year round. These sheets of ice eventually moved slowly southward at approximatly 200 ft per year as their own weight increased (Fleming, 1997; Sherry, 2000).

www.dkrz.de/dkrz/broschuere-eng/research/iceage.html

The extreme exageration of seasonal temperatures that results from the angle of the Earth's axis also affects the climate by providing prolonged periods of cool tmperatures that allow glaciers to form. Thus it is no surprise that glacieral events coincide with the phases of the Earth's tilted axis (Elias, 2002).

Impact in the United States

Glacieral contact with the contents had drastic affects on the physical features of the land. In the Midwest region of the United States, glaciers destroyed any fossil remants of dinosaurs that may have existed in that area. The the soil in these regions is also rich in silt from deposits carried by glaciers (Geobopological Survey, 2000).

The formation of the Great Lakes is another physical feature created by glaciers. When the glacier in North America began to melt and receed due to increased climate temperatures, the water left behind was deposited into what is now the Great Lakes (Geobopological Survey, 2000).

Literature Cited

Maasch, Kirk A. 1997. The big chill. http://www.pbs.org/wgbh/nova/ice/chill.htm Accessed 15 Jan. 2002.

Denver Museum of Nature and Science. 2002. Ice age. http://www.dmns.org/iceage/index.html Accessed 15 Jan. 2002.

Sherry, Ned. 2000 Dec. 7. The pleistocene epoch and its impact on Ohio. http://dept.kent.edu/geology/sclement/history/casestudy/pleistocene/pleistocene_files/frame.htm Accessed 15 Jan. 2002.

Geobopological Survey. 2002. The pleistocene epoch. http://www.geobop.com/paleozoo/Time/ Cenozoic/Pleistocene/ Accessed 17 Jan. 2002.

Fleming, Anthony. Dec. 1997. Freeze frame: the ice age. http://adamite.igs.indiana.edu/indgeol/time/ Frzframe.htm Accessed 17 Jan. 2002.

Elias Scott. 2002. What caused the ice age. http://culter.colorado.edu:1030/~saelias/glacier.html Accessed 18 Jan. 2002.

Ray, Elias L. 2002. The great ice age. http://pubs.usgs.gov/gip/ice_age/ Accesseed 15 Jan 2002.

Illinois State Museum. 2002. Ice ages. http://museum.state.il.us/exhibits/ice_ages/ Accessed 18 Jan. 2002.

DKRZ. 30 Sept. 1994. Ice age climate. http://www.dkrz.de/dkrz/broschuere-eng/research/iceage.html Accessed 15 Jan 2002.

Copyright ©-2001 Earlham College. Revised 25 February 2002. Send corrections or comments to riethju@earlham.edu