Fire Stone: First Fire-Scorched Petrified Wood Found

This rosy-pink chunk of petrified wood from Utah's Chinle Formation is the oldest-known fire-scarred fossil.

(Image credit: Bruce Byers)

SACRAMENTO, Calif. — After serving nearly 30 years as a doorstop for a nuclear physicist, a hunk of petrified wood from Arizona has finally been recognized as a one-of-a-kind find. The 210-million-year-old piece of wood contains the first fossilized fire scar ever discovered, researchers reported here this week at the Ecological Society of America's annual meeting.

Evidence for ancient forest fires predates the dinosaurs, but the clues come from charcoal, not from marks on fossilized trees. Charcoal remains of Earth's oldest fires date back more than 400 million years. No one has ever spotted a fire scar on petrified wood before, said lead study author Bruce Byers, a natural resources consultant from Falls Church, Virginia. That's because the scientists who study petrified wood rarely cross paths with forest fire researchers, Byers suspects. But Byers thinks more fossil fire scars will be found.

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Byers spent two decades staring at his father's 16-pound (7 kilograms) doorstop before realizing it might be from a fire-scarred tree. His father, Cleo Byers, was a nuclear physicist for Los Alamos National Laboratory in New Mexico, and took his children on hikes throughout the Southwest, Bruce Byers said. The rosy-pink stone came home with father and son 28 years ago, after a hiking trip near Utah's Bears Ears Buttes. The colorful chunk was collected on national forest land, where it's legal to take petrified wood by permit, according to Byers, who has detailed the story on his blog. The petrified chunk likely came from the Chinle Formation, the same wood-rich rock layer that litters Arizona's Petrified Forest National Park with huge, crystallized trees. [Photos of Arizona's Amazing Petrified Forest]

With networking and cold calls, Byers put together a dream team that could help him polish his findings and publish the results in a scientific journal. The study will appear Oct. 1 in the journal Palaeogeography, Palaeoclimatology, Palaeoecology. His collaborators include the University of New Mexico's Sidney Ash, who may have looked at more petrified wood from the Southwest than anyone else on Earth; Dan Chaney, an expert on ancient plants at the Smithsonian National Museum of Natural History; and Lucía DeSoto, a professor at Portugal's University of Coimbra and a leader in analyzing tree growth, cell by cell.

One of the team's key findings was that the petrified tree seemed to react to fire stress in the same way as modern trees. Stress from forest fires can leave behind bands of narrow tree rings in some modern trees, a result of the struggle to recover and grow. The ancient tree was a species called Agathoxylon arizonicum, a species that never forms growth rings. However, its microscopic tree cells, called tracheids — internal highways that transfer water and nutrients — show signs of fire stress in a manner similar to tree rings. Six to eight rows of tiny tracheids suggest suppressed growth immediately after the fire, the researchers report. The next rows are bigger than prefire tracheids, likely because the forest fire's survivors had less competition for water and nutrients, Byers said. This post-fire growth spurt is also seen in modern trees.

Becky Oskin covers Earth science, climate change and space, as well as general science topics. Becky was a science reporter at Live Science and The Pasadena Star-News; she has freelanced for New Scientist and the American Institute of Physics. She earned a master's degree in geology from Caltech, a bachelor's degree from Washington State University, and a graduate certificate in science writing from the University of California, Santa Cruz.