When Does a Forest Become Petrified?
A forest becomes petrified or turned to stone under certain conditions, through the action over the centuries of water containing large quantities of minerals.
Tree trunks buried ages ago under mud, sand or volcanic ash have been gradually transformed as water seeped into the empty cells of the decayed wood, filling them with mineral matter and preserving every detail of the original structure.
Petrified forests have been found in many parts of North and South America, dating from different geological periods and containing stone replicas of the trees that grew in those eras. The most famous of these forests is the Petrified Forest National Park in north Arizona, in the United States.
There thousands of stone trunks and logs have been exposed to view through the rain washing away the soil in which they were buried. Although now composed of a mineral called silica, the original details of the trees can be studied through a microscope.
Some of the trunks are up to 80 feet long and three to four feet in diameter. They are the fossils of cone-bearing trees belonging to Triassic times, the age of the dinosaurs, and are more than 150 million years old.
Unlike other types of fossils which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material. The petrifaction process occurs underground, when wood becomes buried under sediment or volcanic ash and is initially preserved due to a lack of oxygen which inhibits aerobic decomposition.
Mineral-laden water flowing through the covering material deposits minerals in the plant’s cells; as the plant’s lignin and cellulose decay, a stone mold forms in its place. The organic matter needs to become petrified before it decomposes completely. A forest where such material has petrified becomes known as a petrified forest.