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Rock or Wood -- What Is This Stuff?

It looks like a weathered, multicolored tree limb, shining and sparkling in the light -- but it's heavy, hard, and solid as a rock. Just what is this stuff? It's petrified wood.

Back in the old days -- some 135 to 155 million years ago -- southern Utah was not at all like you will see it today. It was closer to the Equator than it is now, which made it a wet and hot land, with lots of ferns, palm trees, and conifers providing lunch for the neighborhood dinosaurs.

Occasionally, floods would uproot the trees, dumping them in flood plains and along sandbars, then burying them with mud and silt. If this happened quickly, the layers of mud and silt would cut off the oxygen supply, halting the process of decomposition -- and effectively preserving the tree trunks intact.

Later, volcanic ash covered the area, and groundwater rich in silicon dioxide and other chemicals and minerals made its way down to the ancient trees. With the silicon dioxide acting as a glue, the cells of the wood mineralized. Other waterborne minerals produced the colors: Iron painted the tree trunks in reds, browns, and yellows; manganese produced purples and blues.

Sometime afterward, uplift from within the earth, along with various forms of erosion, brought the now-petrified wood to the surface in places like Escalante Petrified Forest State Park and Grand Staircase-Escalante National Monument, breaking it into the shapes of today in the process -- one that's taken only a hundred million years or so to complete.

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