Triassic Petrified Wood Specimen

Araucarioxylon arizonicum, ca. 275 Ma, petrified wood specimen, 12 x 15 in., Beneski Museum of Natural History. Photo by author.

Galaxy Suspended: A Poetic Reflection

Araucarioxylon arizonicum, ca. 275 Ma, petrified wood specimen, 12 x 15 in., Beneski Museum of Natural History. Photo by author.

Object Description

Viewing only its exterior, the fossilized tree bark is the only indication that this specimen of petrified wood once belonged to a living organism. Standing at approximately 12 inches tall and 15 inches wide, the first characteristic that unequivocally grabs the viewer’s attention is the colorful, hardened cross section. The faint outlines of growth rings circle the milky white center, blending the colors together and reminding the viewer of a galaxy. Dotting the edges is a mix of red and black, smoothed over almost too perfectly. Upon closer inspection, the brown-colored minerals dotting the growth rings have a crystalline appearance. At the center, the faint red color grabs the viewer’s attention, distinguishing it from the rest of the piece. An even closer inspection reveals the layering of the colors throughout the specimen. 

Scientific Formation and Composition

Petrified wood formed through a process called silicification, and occurred in environments with high levels of volcanic activity. Eruptions led to an abundance of silica in the environment, which enveloped tree trunks in a mineral-rich volcanic ash. Over time, groundwater transported the ash into the highly porous wood. Because wood cell walls have a high affinity for silica, the mineral easily binds to the structure. It replaces the parts of the wood that would otherwise decay, filling the interior with a stone-like fossil. Remarkably, many pieces of petrified wood maintained their original structure, leading scientists to believe this process occurred shortly after burial.¹ However, due to varying environmental conditions, such as differences in temperature and amounts of silica, scientists have yet to agree upon a concrete time scale that petrification occurred over.²

A 2016 study out of Western Washington University and the University of Oregon revealed the color of petrified wood arose from trace amounts of just a few elements.³ In comparison, certain physical and chemical factors create the intricate textures and patterns. For example, the fibrous wood structure scatters light within the core, resulting in opaque features. Tiny bubbles of liquid trapped during mineral formation explain the pure white center.⁴ Deep red tones came from oxidized iron, the same chemical change that gives rust its distinct color. As the shades of red vary, so does the amount of iron and its oxidation state. Higher amounts of oxidized iron results in a darker appearance, whereas iron in a reduced state causes a lighter appearance. ⁵Furthermore, silicification occurred over multiple stages, with groundwater moving through the specimen more than once. When two or more color-causing minerals were present, they blended together to form layered patterns.⁶

Petrified Wood as an Ancient Climate Archive

The movement of mineral-rich groundwater is a distinct feature of the petrification process. Groundwater movement is also connected to ancient weather patterns, as it plays a crucial role in the water cycle. Forces such as precipitation, temperature, and seasonal cycles directly influence the ancient current. Each specimen of petrified wood retraces its flow, shaping the broader climatic conditions of the ancient world.⁷ 

For example, a 2018 study from Rice University dated and compared specimens of petrified wood from two beds in Petrified Forest National Park. Their study explains the dramatic color differences between samples from the Rainbow Forest Bed and Black Forest Bed. Using new uranium-lead dating methods, they uncovered how shifts in isotope composition shape an understanding of the minerals that once coated the ancient floor.⁸ In this way, petrified wood becomes a natural archive of the ancient climate, preserving the rhythms of drought, rain, heat, and seasonal changes. 

Desire, Interference, and the Conscious Pile

The mysterious colors and supernatural composition naturally intrigues visitors of Petrified Forest National Park. Unsurprisingly, this leads people to illegally remove specimens from the park, despite threats of fines and vehicle inspections. Up until 2015, an exhibit in the visitor’s center warned that 12 tons of rocks per year were disappearing, signaling that none would be left for future generations to see in the near future. Since then, that estimation has gone significantly down.⁹ However, the display also contained letters enclosed in the packages sent back by remorseful thieves. Many reference a curse that fell upon them due to wrongful possession of the petrified wood. 

This led to the creation of the “conscience pile.” 

Located off of a private service road and unmarked on park maps, park officials have designated this space as the dumping grounds for returned specimens. Because of their unknown provenance, returned samples of petrified wood cannot be put back in their original location, as it would interfere with the field research occurring at the site.¹⁰ The conscience pile serves as a reminder of the one-way, often irreversible relationship between humans and climate. Attempts to control pieces of the ancient climate erase vital evidence of prehistoric rainfall, seasonal rhythms, and groundwater patterns, which are the keys to reconstructing Earth’s past climate. 

Controlling the Climate—By Way of Conclusion

This theme of human desire to control and master the natural world is not new, manifesting itself in art installations throughout the 21st century. Olafur Eliasson’s The Weather Project uses industrial materials to fill The Turbine Hall at Tate Modern with a vast, artificial sun. Nonetheless, people interact with it as though the lamps and mist are truly our star, lying on the ground and bathing in its glow. The Weather Project is ultimately an artificial environment, one that looks to represent weather through a self-contained, controlled environment. This displays an obsession with the unnatural rather than the natural, linking our relationship with climate to spectacle. 

This desire to master and control the weather is reflected by the conscience pile, serving as a reminder of human fascination with climate control causing irreparable damage. Each specimen laid to rest in the pile has a story that will remain untold as a consequence of human interference. Fragments of the ancient climate are turned to anonymous stones. Only after the fact, when the rumblings of a curse stir human conscience, is when remorse sets in. As a monument to human impulse, the conscience pile is a site where the voice of the ancient climate is silenced forever.

Footnotes

1. Hehe Jiang, Cin-Ty Lee, and William G. Parker, “Trace Elements and U-Pb Ages in Petrified Wood as Indicators of Paleo-Hydrologic Event,” Chemical Geology 493 (2018): 267. ↩︎
2. Elisabeth A. Wheeler, “Fossil Woods of Yellowstone National Park,” Parks Stewardship Forum 40, no. 1 (2024): 183. ↩︎
3. George Mustoe and Marisa Acosta, “Origin of Petrified Wood Color,” Geosciences 6, no. 2 (2016): 3. ↩︎
4. Mustoe and Acosta, “Petrified Wood Color,” 2. ↩︎
5. Mustoe and Acosta, “Petrified Wood Color,” 4. ↩︎
6. Jiang et al., “Ages in Petrified Wood,” 279. ↩︎
7. Jiang et al., “Ages in Petrified Wood,” 267. ↩︎
8. Jiang et al., “Ages in Petrified Wood,” 279. ↩︎
9. Nicola Twilley, “Slide Show: Rocks, Paper, Sinners,” The New Yorker, January 23, 2015. ↩︎
10. Twilley, “Rocks, Paper, Sinners.” ↩︎