Which is the older mountain chain, the Appalachians or the Rockies? What does this tell us about how North America was formed?
The Appalachian Mountains are much, much older than the Rockies. The Appalachians were created starting 470 million years ago and ending 250 million years ago. During this time, what's now North America was part of Pangaea.
By contrast, the Rockies were formed around 15 million years ago. They are believed to have been created by one tectonic plate subducting under another.
I guess what this tells us is that North America was formed by the collision of a lot of different plates and that it is not just all on one plate.