Darline Shinell, age 11, of St. Louis, Mo., for her question:

WHICH WERE THE VERY FIRST MOUNTAINS?

Mountains are made by the earth's restless crust, which first formed more than 4 billion years ago. Most likely the very first mountains were formed at this time or soon after. However, the original crust has been remodeled many times. All signs of its original mountains were erased long ages ago. So the very earliest ranges were lost, and nobody even can guess where they were.

The weather is constantly eroding the mountains, and after hundreds of millions of years the lofty ranges are worn down to gentle hills. The gentle hills of the Laurentians in eastern Canada are the worn down roots of proud mountains that formed more than half a billion years ago. These are the earliest mountains we know about. But most likely still earlier ranges disappeared long ages ago.