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LEARN ABOUT POLAR BEARS IN THE NEXT INSTALLMENT OF WORLD OF WONDER© 2012 Triefeldt Studios, Inc.Distributed by Universal Uclick for UFS

At a bookstore near you: Two full-color World of Wonder compilations: “Plants & Animals” and “People & Places.”

SOURCES: World Book Encyclopedia, World Book Inc.; www.kidskonnect.com; Glacier National Park; Illinois State Museum; www.nature.ca; www.zoomdinosaurs.com; www.athropolis.com; National Snow and Ice Data Center

Did you know?•Glaciersthatexisttodayareleftover from the Great Ice Age.•Wearetechnicallystillinaniceage since there are two major continental ice sheets on Earth: Greenland and Antarctica.•Dwarfwoolymammothssurvivedon an isolated island as recently as 5,000 years ago before be-comingextinct.•Swiss-bornscientistLouis Agassiz (1807-1873) was one ofthefirstscientiststostudyiceages. He proved that the move-ment of the glaciers created lakes and shaped the landscape.•Iceagepeoplelived35,000yearsago. They hunted mammoths and other creatures for food and clothing. Nothing would have been wasted.•About18,000yearsago,therewere glaciers in Hawaii.•Today,glaciersstoreabout75percent of the world’s fresh water.•Ifalllandicemelted,sealevelwouldriseapproximately230feet(70 meters) worldwide.•Glaciericecrystalscangrowtobe as large as baseballs.•NorthAmerica’slongestglacieris the Bering Glacier in Alaska, measuring 127 miles (204 km).

Why glacial ice appears blue: When glacial ice is compressed, air pockets are forced out and it becomes very dense. This dense ice absorbs all other colors in the spectrumandreflectsprimarilyblue, which is what we see.From the 17th century to the late 19thcentury,theworldexperi-enced a “Little Ice Age,” when temperatures were consistently coolenoughforsignificantglacieradvances to occur.

Unlike the dinosaurs, woolly mammoths shared the Earth with people. They lived from the Pleistocene to the early Holocene epoch (about 10,000 years ago). Now extinct,theherbivorousmammalslivedin the tundras of Asia, Europe and North America. Closely related to modern-day Indian elephants, these giants grew to about 11.5 feet (3.5 m) long and 9.5 feet (2.9 m) tall at the shoulder. They weighed about3tons.Frozen,naturallymummifiedmammoths have been found in Siberian ice.

Mastodons were large, elephantlike herbivores with tusks, grinding molars, a long proboscis (nose) and large ears. They evolved during the Oligocene epoch and are closely related to mammoths and elephants. They lived until about 10,000 years ago. (A few species lived longer.)

Smilodon, the largest saber-toothed cat (also known as the saber-toothed tiger), was a fiercepredatorthatranin packs. At 4 to 5 feet (1.2 to 1.5 m) long, this dangerous carni-vore may have eaten thick-skinned prey like mastodons. Thousands of fossils have been found in late Pleistocene tar pits and rocks from North America and South America.

Megatherium (pronounced MEG-ah-THEER-ee-um) was a

giant ground sloth; its name means "great beast." Megath-

erium was about the size of an elephant. It was a slow-moving

plant-eater with peglike teeth and powerful jaws. It lived during the Pleistocene ep-och in what is now South Americaandwentextinctabout 11,000 years ago.

Present day ice cover

Ice Age ice cover

A big differenceDuring the Great Ice Age, the Earth was much colder than it is now. Glaciers and ice sheets covered large areas, and the sea levels were lower. The maps below compare the ice coverage of North America today and during the last ice age.

Uintatherium (pronounced you-

IN-tah-THEER-ee-um) was a huge, rhinoceros- like mammal (not a dino-

saur) of North America.

About 11 ice ages have occurred during the Earth’s 4.6 billion years of existence. The most recent, the Great Ice Age, began about 2.6 million years ago and continues today.

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The Great Ice AgeThe current ice age (also known as the Pliocene-Quaternary glaciation) peaked about 20,000 years ago, and its active “glacial” period ended about 11,700 years ago. Since then, we have been in an “interglacial” period.Today, about 10 percent of land is cov-ered by glaciers. During the peak of this ice age, 32 percent was covered by ice.

Living on the ice The Pleistocene era began 1.8 million years ago and ended about 10,000 years ago. Many of the animals ofthattime(suchasmuskoxen,elk,bisonandsmaller tree sloths) still roam the Earth today. Oth-ers, like the saber-toothed cats, giant ground sloths, mastodonsandmammoths,havebecomeextinct.Environmental changes, disease and human hunting probablyplayedaroleintheextinctionofmanyofthese animals. We have learned about them from fos-sils, frozen mummies and ancient cave drawings.

By definitionIce ages are periods when large areas of the Earth are covered by ice sheets, or large continental glaciers. During an ice age, the weather has cold spells called glacials and warm spells called interglacials.

Changing landscapeMany glacial advances and re-treats have occurred over the last billion years of Earth’s history, and they have had an enormous impact on the landscape. As glaciers and ice sheets ad-vanced and retreated, they changed the surface of the Earth. They formed lakes, moved rivers, eroded land and deposited sand, gravel and rocks along the gla-ciers’ paths. It is estimated that more than 60 glacial advances and retreats have occurred during the last 2 million years.