Answer:
They formed years ago and erosion has reduced them to their current height
Step-by-step explanation:
The Appalachian mountains are about 400 million years old compared to the Himalayas which are about 50 million years old. Thus, it is possible for the Appalachian mountains to have been as high as the Himalayas but the exposure of the Appalachian mountains to erosion long before the Himalayas were formed could be the reason for its reduced height compared to the Himalayas.