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How Trees Become Rocks

Wiki Commons
A sliced and polished round of petrified Juniperus species wood. Oligocene, Elko, Elko County, Nevada, USA. On display at the 2009 North Seattle Lapidary and Mineral Club Show.

On a recent camping trip in Nevada, I visited a display of petrified wood. A tall chain link fence surrounded the logs — as if they were in prison — to protect them from people who might grab pieces as souvenirs.

What makes these logs so special? Petrified wood is a very particular type of fossilized wood. Those logs are over 200 million years old, but amazingly, still retain the same shape and structure as when they were alive. Biologically, the original trees are related to our current-day ginkgos and Norfolk Pine trees.

The process of trees turning to stone started pretty simply: water washed logs into ancient river systems, burying them so deeply that it cut oxygen off. Then, bacteria and fungi — which need oxygen — couldn't decompose them. Instead, water, containing all kinds of dissolved minerals, flowed through the porous wood, replacing every single cell of organic material with crystals.

Petrified forests can be found all around the world. In Utah, we can see petrified wood in Grand Staircase–Escalante National Monument.

Another reason petrified wood must be protected is because of its beauty. Each piece is a giant sparkly quartz crystal, with a rainbow of colors produced by imbedded minerals: cobalt creates greens, iron oxides create reds and manganese makes pinks and oranges.

So trees can turn into rocks. Can rocks turn into trees? Yes! Trees get their nutrients, water and support from soil, which is originally derived from rock.

The dynamic process of soil formation happens through the slow but unstoppable forces of physical, chemical and biotic weathering. When moisture seeps into cracks and then freezes and expands, it literally busts the rocks apart. And when water combines with carbon dioxide, either from the air or in the soil, that reaction creates carbonic acid, which can chemically dissolve rocks.

So, trees can turn to rocks and rocks can turn into trees, if we give them enough time.

But rock time and tree time pass in different scales. As poet Bill Yake wrote, "To the rocks, the trees are just passing through."

Dr. Nalini Nadkarni is an emeritus professor of both The Evergreen State College and the University of Utah, one of the world’s leading ecologists and a popular science communicator. Dr. Nadkarni’s research and public engagement work is supported by the National Geographic Society and the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. @nalininadkarni
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