Harold Saack, age 11, of Rockford, OR for his s question:

Why do objects petrify?

A petrified object is made of stone, though it was once a living thing. It may have been a tree, a shell, an animal or any part of these things, The most famous of these objects are the stone tree trunks of the petrified forests, These trunks were once mighty trees in some crowded forest that thrived millions of years ago. The climate changed and the area fell upon hard times. The forest was covered with a dry, sandy desert.

Through the ages, the showers that drenched the ground were few and far between. Much of the water sank through the soi3s dissolving its chemicals. This water seeped into the buried trees and dissolved their woody tissues. The process was slow and, as the wood dissolved, it was replaced by chemicals in the water. The living tissue was replaced, molecule by molecule, with stony chemicals, After millions of years, the great tree trunks were made entirely of stone.