The Appalachian Mountains in eastern North America are old. Like, ridiculously old. They first formed around 480 million years ago, before fish had evolved jaws, before trees existed, and long before any dinosaur stomped around.
Back then they were as tall as the Himalayas are today, with jagged peaks several kilometres high. But almost half a billion years of wind, rain, and ice have worn them down to gentle rounded hills, most no more than 2,000 metres tall.
The Appalachians also have a long-lost twin. When the supercontinent Pangaea split apart, the same mountain range was torn in two - half stayed in North America, the other half drifted away and became mountains in Scotland and Norway.
