Steven Martin, age 7, of Phoenix, Arizona, for his question:

How did the seashells get on the deserts

Once upon a time, millions of years ago, a shallow sea once flooded our western deserts. Its waters teemed with all kinds of living creatures  fishes and shellfish.

The shills of many of these cr natures sank to the bottom of the wster and stayed there. In time, they were turned into stoney fossils by seeping water. Gradually the ancient sea drained away, leaving the seashells embeded in the dry land.

Some of the shells you find in the desert might well be these precious fossils   the remains of the creatures that lived before the Rocky Mountains raised their proud heads to the sky.