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Evidence from the Past

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Rocks and fossils provide evidence of earlier lives and environments. Interpreting the specimens allows a geologic and zoological history of an area to be written. You may  discover interesting rocks and fossils as you walk the stream valleys and rock outcrops of Iowa.

A concrete sidewalk is a human-made layer of rock. It is composed of rock fragments and binding material shaped by confoming borders. Simple tools mix sand, water, and portland cement together to form a rock-like sidewalk. A wooden form holds the mixture in place until it hardens. Like a fossil in a rock, a leaf or footprint in wet cement remains after the cement hardens. Cement forms when limestone and clay are burned together and then ground into dust. Iowa is the leading producer of portland cement.  



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