Montshire Minute: Ice Ages

Originally aired during the week of January 18, 1999

Monday

What's the biggest ice cube you can imagine? How about one that covers most of Canada and the northern United States? If you could travel back in time about twenty thousand years ago, you could see it for yourself - the great Laurentide ice sheet, which covered all of New England and parts of the northern Plains states. The term "Ice Age" refers to cooler than normal periods in the earth's history. An ice age may consist of several "glacials," times when glaciers reach their peak, and warmer intervals called "interglacials," when the glaciers recede. Scientists believe at least four glacial advances and retreats have occurred during the last two million years. In fact, the entire history of modern humanity may be taking place in one of these interglacial periods. Which means we're really smack in the middle of an Ice Age! Cool!

Tuesday

You think it's cold now? Thousands of years ago, all of New England was covered by a blanket of ice - the great Laurentide Ice Sheet. After 20,000 years of melting, there's not much of it left - just some ice fields in the western mountains and ice caps in the Arctic islands. But some researchers think we may still be in the middle of an Ice Age. To be more exact, we're living in the Holocene Interglacial - a slightly warmer period that precedes yet another advance of the ice sheet! Over the past two million years, a period known as The Pleistocene Epoch, there may have been at least four glacial advances and retreats. You can learn more about the most recent ice age and the many incredible (and now extinct) creatures that inhabited the earth back then when you visit Mammals of the Ice Age exhibit, on display at Montshire beginning Saturday, January 23rd.

Wednesday

During the ice ages, huge sheets of mile-thick ice ground across the North American continent. The glaciers scoured the earth's surface, bulldozing the soil in front of it. Unfortunately for New England farmers, much of the region's topsoil was plowed off the coast of Connecticut, creating Long Island. As the ice retreated about 10,000 years ago, meltwater collected in ice-dug hollows. Three major lakes were formed in what is now New England, including Lake Hitchcock, which covered 160 miles of the present day Connecticut River Valley. The northern end of the lake was located about where Lyme, New Hampshire, is today, and the water level was as high as the Tower of Dartmouth College's Baker Library. A great dam of glacial deposits left behind by the glacier eventually broke in the vicinity of Haddom, Connecticut, draining the lake and leaving the Connecticut River.

Thursday

Montshires' Mammals of the Ice Age exhibit includes complete skeletons of eight mammals that lived during the Pleistocene Epoch (between 10,000 and two million years ago). These were pretty impressive animals. For one thing, many of them were a lot bigger than their present-day relations. The giant beaver was a rodent that could grow to be larger than a modern black bear. Why were these animals so large? High winds and low temperatures were pretty much the norm across the tundra landscapes bordering the great glaciers. After all, this was the Ice Age! In his book Reading the Forested Landscape author Tom Wessels points out that being big was a survival mechanism. Mammals like the great woolly mammoth needed to conserve body heat by increasing the volume of their bodies in relation to their surface area.

Friday

What causes Ice Ages? One theory relates to the shifting of the earth's crust, which influences the direction of warm ocean currents. Between two to seven million years ago, warm Atlantic waters flowing along the North American coast kept a steady flow of temperate water pumping into the Arctic Ocean. That, so the theory goes, prevented glaciers from forming. When the central American isthmus emerged, connecting North and South America, this current changed. The belt of warm water joined the Gulf Stream, moving east across the Atlantic Ocean, and then south towards the coast of southwest Africa, finally circulating back into the Indian Ocean. This created a "conveyor" effect, which prevented warm water from flowing into the Arctic Ocean and encouraging glaciers to form.