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The Archeological History of Iowa

The history of Iowa is the story of the land as much as the story of the people who came to live here. Throughout the year we expect each of the four seasons to change the appearance of the land. But we don't expect the land itself to change very much over time. However, before people ever came to live in our state, the beautifully cultivated farmland we now know as Iowa, changed dramatically.

Strip cropping in Dubuque County, IA.

In 1836, before Iowa was a state, Albert Lea explored what we now know as Iowa. He described the natural prairies, the flowing rivers and the forests he encountered. But these features were actually the product of millions of years of natural development.

Iowa's land has been through a lot of change and it even traveled some, too. The fossil records found along Iowa streams and rivers tell us that Iowa's land was once under the sea. Later it was a warm tropical environment. Still later, Iowa was covered with up to a mile of ice. When the ice receded, the prairies developed. Let's look at each of these phases a little more closely.

In the beginning…most scientists think that billions of years ago the earth was a ball of lava, red-hot lava! Over long periods of time, this large ball of lava began to cool. Sheets of rock formed to make the beginnings of what we know today as the continents. Called plates, the continents drifted slowly inch by inch. These movements took millions of years. At one time Iowa may have even been located somewhere near the equator with mountains and a tropical climate.

A Manila dwarf coconut palm on the grounds of the Tropical Agriculture Research Station in Mayaguez, Puerto Rico.  Photo by Scott Bauer.As the plates or continents drifted apart, the shape of the oceans changed. Iowa's land actually took a dive. During that time Iowa acquired layers of limestone, sandstone and even coal.

Scientists believe that at this time Iowa was at the bottom of a warm, shallow, swampy sea! Layers of sand, shells and other natural materials formed a thick layer of sandstone that covered the land. This porous layer of soft sandstone rock holds water very well. Today many Iowa towns tap this layer of rock when digging wells for their communities.

As more plants lived and died in these warm shallow seas, the dead plant material was buried under layers of mud. Slowly it changed into coal. Today, coal can be found under much of the land in southern Iowa.

The layers of limestone found in northeast Iowa also formed under the sea millions of years ago. Today these beautiful rock formations provide scenic views and a wonderful and unusual cave system.

Then, about two million years ago, the land began to cool and Iowa became dry land. Scientists are not sure why, but snow fell and didn't melt from season to season. Large layers of ice formed north of Iowa in Canada. The ice began to flow slowly south until it covered all of the central United States. It was up to a mile thick in some places. Then the climate would become warmer and the ice would recede. When the thick layer of ice moved back north, the land was changed again. Boulders, small rocks and gravel carried by the glacier flattened and smoothed the land like sandpaper. As the ice melted, streams formed through the layers of soil left by the glacier.

Scientists think the ice came and went over many parts of Iowa at least four times. The last layer, called the Wisconsonian, covered north central Iowa, reaching south to about the area of Des Moines. This glacier just "recently" melted. Actually, it was twelve thousand years ago, but considering the amount of time that passed with each phase of Iowa's geological past, twelve thousand years isn't much time!

Bob Schnieder (l) and Ed Weilbacher look over grasses Bob planted on his property to support wildlife in the Venedy, IL area.  USDA Photo by: Ken Hammond.

When the glaciers left, the cool moist climate produced rich forests. Spruce and pine covered most of the state. Then the climate became drier and warmer and hard wood trees like oak and walnut began to replace the evergreen trees. As the climate became even drier grass areas began to form in patches between the forests. Gradually the forested areas gave way to the natural prairies of Iowa. This is the land that Indians and later the pioneer settlers found as they came to live in Iowa.

 

 
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