Here's why:

* Pangaea formed around 335 million years ago. This supercontinent existed for millions of years before beginning to break apart around 175 million years ago.

* The Rocky Mountains began forming about 80 million years ago during the Laramide Orogeny. This means they were formed long after Pangaea had begun to break apart.

Therefore, the Rocky Mountains are significantly younger than the supercontinent Pangaea.