Manson crater
The Manson crater is an impact crater near the site of Manson, Iowa. An asteroid or comet nucleus struck the Earth during the Cretaceous Period, approximately 74 million years ago. The event was one of the largest known impact events in North America.  Until they found the ages of certain isotopes at the site, people believed that the event caused  extinction of the dinosaurs. The ages sugges that the crater is too old.