The recent meteor explosion over Russia was a close call, but Iowa wasn’t so lucky 470 million years ago.
An ancient meteor gouged a 5.5 kilometer (3.4 mile) crater into was it now northeast Iowa. Aerial surveys recently confirmed the presence of the impact site, according to the U.S. Geological Society.
Geologists from the Iowa Department of Natural Resources first found evidence of the crater in 2008. Rock from a water well boring operation revealed a circular layer of shale under the town of Decorah, Iowa. The tell-tale shale deposits were left by sediments from water that filled the crater after the impact.
A later study by the Smithsonian’s National Museum of Natural History found shocked quartz in the area, a stony smoking gun left by an extraterrestrial impact.
The aerial survey that recently confirmed the craters’ existence used an electromagnetic system, which measured how well rocks conduct electricity, and a gravity gradiometer, which senses subtle changes in the Earth’s gravity. Computer models created using the data from these instruments showed a layer of pulverized rock beneath the shale and helped define the outline of the crater. The differences in the rock of the crater extend to a depth of several hundred meters.
IMAGE: The outline of the Decorah impact structure. (Adam Kiel, Northeast Iowa RC & D, USGS)