“Stone Trees”

Have you ever seen a stone tree? While the idea of a stone tree may sound fantastic, fallen trees can turn to stone in very specific circumstances, producing what scientists call “petrified wood.” “Petra” means stone in ancient Greek, so something “petrified” has been turned to stone. You may have heard the word “petrified” used to describe someone so scared that they have frozen as if turned to stone, but scientists use the word literally to refer to actual stone. Petrified trees are stone trees, not scared trees!

A Type of Fossil

Like ancient skeletons of dinosaurs and other organisms preserved in the earth, petrified wood is a type of fossil; however, there is a big difference between petrified wood and most fossils. Most fossils are imprints of creatures or partial remains of them, such as their skeletons. In contrast, the process of petrification recreates an entire preserved tree in stone. It’s very cool to see a petrified tree close-up, because it is still precisely life-size; you can get an idea of how big the tree was when it was alive, and even see individual tree cells that have been preserved. You can even count the tree rings in some petrified trees and estimate how old the tree grew to be before it was petrified.

From Tree to Stone

In order for a tree to become petrified wood, it must have died and been buried a very long time ago. This has to have happened in a specific environment, though, or petrified wood would not be so rare. The tree has to be buried in such a way that oxygen cannot get to its bark and wood. If oxygen can get to the tree, it will rot instead of turn to stone. 

The environment has to have two more specific characteristics to produce petrified wood: there has to be water in the ground around the tree, and that water has to contain minerals. If mineral-containing water is present, water will go into and out of the tree’s cells and, over time, the minerals in the water will accumulate in the tree’s cells. When the tree’s cells eventually decay, the minerals are left. Petrified wood can be a rainbow of different colors, with each color corresponding to different elements in the tree’s preserving environment that affect the color of the minerals that form its stone.

Petrified wood is found all over the world, and there are even entire forests of petrified trees that you can travel to go see today. One national park in the United States, Petrified Forest National Park in Arizona, is famous for its many petrified trees. The next time you see a tree, remember, after a few million years in the right environment, it could turn to stone!

In what way does petrified wood differ from dinosaur fossils?