Did Nebraska used to be an ocean?

Yes, much of present-day Nebraska was once covered by an ancient ocean known as the Western Interior Seaway, which existed during the late Cretaceous period, around 100 million years ago. This seaway split North America into two landmasses and created a marine environment that left behind fossils of marine life, such as ammonites and sharks, in the rock layers. Over millions of years, geological processes, including sedimentation and uplift, transformed the region into the landlocked state we know today.