Thank cold weather for our livelihood

This past week, winter's first real snows fell upon Iowa City. To the fanciful at heart, crunching footsteps across the white is a bit like returning to the Ice Age, that time when humanity relied on mammoth and flint spears to survive. A snap of cold wind crystallizes your breath, and you really do wish for a thick fur to pull over your head.

Some scientists say we've never really left the Ice Age, that we're just at the cycle's warm end. For the past 1.8 million years, the snows and glaciers have charged then retreated across the Northern Hemisphere 17 times.

Indeed, just 100 centuries ago - barely a fraction of the time that the earth has been around - huge glaciers dipped into north central Iowa until finally melting and creating the landscape we know today.

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Sometime around 13,000 years ago, the Des Moines glacier lobe stalled in the region as the climate temporarily warmed. Meltwater floods washed open valleys to the south, creating glacial lakes.

As the water evaporated and drained off, our state's greatest inland river basins - the Iowa, Boone, Des Moines, Big Sioux, Rac-coon, Skunk, Little Sioux and Winnebago - formed.

The enormous ice sheets departed Iowa some 5,000 years later, leaving flat tundra covered by a muddle of clay, sand, gravel and boulders. Out of the west, wind blew glacial dust, also known as loess, across much of southern Iowa, forming the soil upon which we plant our corn and soybean fields today. Along the Missouri River, some loess piled into bluffs.

But 10,000 years wasn't enough time for the meltwater to flow out. In north central Iowa, some of it settled upon the plain in swamps. The state's earliest settlers drained those wetlands, making the land good for farming and villages. Pio-neers created the channels that Mother Nature was still working on.

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But good farmland and the rivers our cities now hug is not all the last Ice Age left us.

The state's northeast corner remained uncovered by glaciers, allowing the Iowa Pleistocene snail to eke out a living for more than 400,000 years in that part of the world. It's very existence to-day relies upon rocks that the last Ice Age's cold crack-ed open; thousands of years ago, meltwater drained into the fissures and froze be-neath the ground, creating a habitat that's still frigid even in our summer's heat.

For the Iowa Pleistocene snail, no bigger in diameter than a shirt button, it's perfect quarters. Unfortunately, it's a shrinking environment. The snail can only be found on 37 algific talus slopes in Iowa and Illinois.

Its existence is as dependent as ours is on what the Ice Age left behind.

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As glaciers did not cover all of Iowa during the last Ice Age, humanity was able to subsist below those mountains of compacted snow. More than 200 Clovis and Folsom points - stone tools of flint from before 10,800 B.C. - have been found in Iowa.

Living near streams or rivers, these first Iowans ate deer and small mammals, fished and picked berries - not unlike many of the first pioneers as they waited for their first crops to rise from the fertile soil. But Stone Age Iowans also hunted large game such as mammoth, mastodon, caribou and an extinct form of bison.

Some conjecture that these early humans caused each of these giant beasts to become extinct, just as modern Europeans exterminated passenger pigeons and dodo birds. Perhaps. Most likely the dramatic shift in climate did in these creatures. Could an Arctic polar bear, after all, survive in modern Iowa?

In any case, Stone Age Iowans did not know of guns, axes and plows. Such tools allowed humanity to prosper only in the Ice Age's aftermath.

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Mother Nature may yet have her way with us, though.

Most gaps between glac-iation have lasted only 8,000-12,000 years. We're overdue for another Ice Age.

Following a cooling of average temperatures from 1940 to 1975, many scientists and environmentalists predicted during the '70s that the 18th Ice Age was upon us. These days, though, apocalypse takes the shape of global warming.

Ironically, if we are warming the earth, that nightmare may help us avert the next onslaught of glaciers. Perhaps the question before us is which will be the lesser of two evils: adapting to a cold planet or to a hot one?

As you enjoy your coffee while the flakes swirl on the window's other side, it is something to contemplate.

(originally published Dec. 7, 2003)