Turned to Stone

By Sara Thompson

Special to the Enterprise

One of the petrified logs at Petrified Forest National Park, AZ; Image by Jon Sullivan, from Wikimedia Commons

A common and recognizable fossil is petrified wood. It can be as small as piece that can fit in the palm of your hand or be an entire forest of petrified trees still in the same place after millions of years, and everything in between. Like all fossils, petrified wood needs specific conditions in order to survive becoming fossilized.

The two best ways for a tree to become petrified is to be rapidly buried in either mud or volcanic ash. Both environments are mineral rich and oxygen poor. By reducing the oxygen in an environment, bacteria are unable to break down the organic material or do it too slowly, making it easier for minerals to permeate and replace the organic material in the wood. Rivers and the mud that comes from them are full of dissolved minerals that act as the replacement minerals. Volcanic ash also is very mineral rich, especially in the minerals that contain silica which is the most common mineral found in petrified wood.

Petrified forests are found worldwide, and so far have all been discovered in ancient floodplains or volcanic events. In some places, such as at Petrified Forest National Park in Arizona, are accumulations of trees and driftwood that are rapidly buried by fluvial processes. Others still were buried so rapidly in a flood or volcanic event that the trees and stumps are still standing in place as they were in life millions of years ago. In our own backyard, in Sonoma County, is a petrified forest that contains the largest petrified trees in the world. Even giant redwoods are not immune to petrification if given the right conditions, in this case a volcanic eruption nearly 3.5 million years ago.

Campers in this week’s Fossil Finders Summer Science Camp learned about different types of fossils and how they form. They made their own fossils from plaster, excavated shells and dinosaur figures from blocks and assembled wooden dinosaur skeletons.

Explorit's coming events:

• Though Explorit's museum is currently closed, we are planning on opening a new exhibit with cleaning and safety protocols in place for October 2021.

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