Dramatic Changes in Earth's Temperature Caused Ice Ages

Article excerpt

Byline: J. Hope Babowice

You wanted to know

Steven Clow, 9, of Libertyville, wanted to know:

How did the Ice Age begin?

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For further reading

To learn more about the Ice Age, the Fremont Public Library in Mundelein suggests:

- "The Ice Age," by Darlene R. Stille

- "Glacier," by Brian Knapp

- "Icebergs, Ice Caps And Glaciers," by Allan Fowler

- "Glaciers and Icebergs," by Jenny Markert

- "Icebergs and Glaciers: Life At The Frozen Edge," by Barbara Wilson Glacier Web site at http://www.whislter.net/glacier/coolfact.html

"How did the ice age begin?" asks Steven Clow, 9, a third-grader at Butterfield School in Libertyville.

Bill Burger, a botanist (plant expert) who works at Chicago's Field Museum of Natural History, said scientists believe there have been maybe 20 glacial or ice age periods during the past 2 million years when the Arctic first wore its ice cap.

Currently, we are experiencing an inter-glacial period, a time when the planet is warming. In fact, Burger said Venezuela has lost two glaciers and Mount Kilimanjaro, in Kenya, has lost 40 percent of its glacial top in the last 50 years.

What is a glacial period?

"That is defined by the advance and retreat of ice over the northern part of the planet," Burger said. "It is ideally defined by a big ice covering, and this covering appears in cycles."

Scientists report that perhaps four other ice ages occurred throughout the globe. The ice age resulted when ice remained in summer because temperatures were not hot enough to continually melt the previous winter's snow and ice.

Several factors may have caused the glacial periods characterized by great ice sheets - some 10,000 feet thick - that created a wall and link across the continents. …