The story of how North and South America were settled by the first humans. What I was taught was that the Bering Sea was frozen at the end of the last ice age, and then glaciers opened up and people migrated southward.

The problem is that the timing is too tight and the migration would have to have happened too quickly. Many native groups have long seen this story as flawed, as well.

This was covered in the book "1491", and at the time of publication, researchers weren't quite sure what model to replace it with. Probably some of the migration was using boats along the west coast rather than going over land. That book is getting pretty old now, though, and I'm not sure if or where things have settled out.