Mary Kay Allen, age 13, of Salt Lake City, Utah, for her question:

What are petroglvphs?

A petroglyph is a diagram of some sort, carved or scratched on a stone surface. The most famous petroglyphs were left by the American Indians and have been discovered in many unexpected places, most often in the Great Plains and the Western mountains. The diagrams are not exactly writing, for the native peoples north of the Rio Grande had no written language.. But these rocs scratchings were mast likely their first steps toward written words. Mankind developed the art of writing very, very slowly, stage by stage through countless ages. No doubt other peoples of the world created petroglyphs in the dim past.

Most of the early American petroglyphs have recognizable drawings of people and animals, weapons and tepees and other familiar objects. Strewn among these pictures, there are often unrecognizable lines and geometric figures. Experts are pretty sure that these petroglyphs are messages, though so far nobody has been able to decipher their meanings.