Download Petrified Wood: Hydrated with History

Zoe Hern
Rochelle Johnson
Gipson First Year Seminar
1 December, 2016
Petrified Wood: Hydrated with History
Fossils have a lot to say about the past. They tell a unique story. Such stories are
valuable, considering only a small fraction of living organisms have been preserved in
stone. But fossils are not exclusive to dinosaurs and other immensely interesting
vertebrate. Plants are also fossilized, and reveal groundbreaking information about the
history of the Earth. By examining petrified plants, one not only discovers how the world
formed the object, but how this thing has shaped the world. Petrified wood has meaning,
and by understanding one specimen’s journey, I have uncovered significance.
Petrified woods, such as the specimens in the Orma J. Smith Museum of Natural
History, are literally wood turned to stone. They are not impressions in clay, like most
fossils, but rather have undergone a chemical process where minerals actually replace the
organic material while retaining the tree’s natural structure in a kind of cast. This process
is called permineralization (Daniels 25-27). The more wood-like structure is preserved,
the more impressive truths a specimen holds about the ecological, environmental,
geological, and anthropological story of its region of origin. Some pieces, however, are
completely or nearly fully converted to rock. The better preserved a petrified specimen is,
the greater the monetary and scientific value (Emry). In extreme cases these lack all the
tree rings and cell impressions that are key to identifying the tree species and
reconstructing an ancient climate – though they do make beautiful jewelry or show
pieces.
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Fossils are formed when a living organism is quickly buried alive and
immediately sealed off from the air. The process could occur during a flood, landslide,
glacier, or volcanic eruption. This particular specimen of petrified wood was buried under
volcanic ash and opalized. Rather than being burnt and covered by magma, a volcanic
eruption spews silica-rich ash (SiO2), which falls from the air and dusts the landscape.
The force of the explosion also knocked down many trees. Then in order to be opalized,
“Water from rain or a stream” then hydrates the ash and “dissolves the silica into salt-like
ions and enables them to soak into trees” (Goode). Nate Carpenter, a fossil expert, says
that exactly this happened in Grassy Mountain. Silicon dioxide particles in the ash fell
into some hot springs and permineralized logs that were trapped at the bottom of the
springs (Cummings et al. 679). In some places, the trees were blown into the ancient
stream or lake that existed, when another eruption covered the water in magma, burying
the hydrated vegetation (Carpenter).
In this anaerobic situation, the organic material stops decomposing, and
eventually the ionized water evaporates, leaving behind solid deposits of silicon dioxide
and small traces of other soluble salts, like ferric (iron) oxides (Goode, Carpenter,
Tormey). These silica molecules form a crystal structure as they are distilled and
compressed (Tormey). “When the particles are of similar size and form near perfect
crystal lattices, light is scattered so all colors of light are reflected” – this is precious opal
(Tormey). More common, however, the particles are amorphous in size and line up
irregularly, diffracting light and giving it a milky white or grey color (Tormey). This
common opal is the variety that formed inside this particular specimen. By looking
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closely, one can even see traces of red in this petrified wood, indicating small amounts of
ferric (iron) oxides that were in the volcanic ash.
This piece also holds an incredible history of geologic evolution. It was found
near Grassy Mountain in Vale, Oregon, just north of the Oregon-Idaho graben. A graben
is a geological formation where an area is depressed in a kind of valley, having two
parallel faults on either side. This formation evolved during North America’s tectonic
drift westward during the Miocene, and the Owyhee County (south of the fault) actually
rested above the Yellowstone hotspot (Cummings et al. 669). As the continent drifted,
molten materials rose near the surface and probably touched underground lakes
(Cummings et al. 674). This caused the water to turn into steam, creating pressure
underneath the crust, multiplying the stress already occurring as the tectonic plates
shifted. Lava flowed through buttes and rhyolite volcanoes, creating “tuffaceous silt and
mudstone” formations surrounding the graben about 15.3-14.3 million years ago
(Cummings et al. 672). Then, 14.3-12.6 million years ago, calc-alkalic volcanoes (having
more fluid lava with low silica concentrations) became extremely active, creating
massive basalt flows (Cummings et al. 674). Approximately 13.1 to 12.6 million years
ago, Grassy Mountain spewed lava with high silica content, resulting in the
permineralization of vegetation (such as this tree) and eventually forming precious
crystalline structures (Cummings et al. 677). Grassy Mountain was a fairly dangerous
rhyolite volcano because it spat high concentrations of silicon dioxide (SO2) (Harris 31,
Cummings et al. 677). These eruptions petrified this exact piece of wood. Fossilization no
longer occurs along the Oregon-Idaho graben because as this area moved further and
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further from the Yellowstone hotspot, eruptions became less frequent until every butte
became dormant.
Petrified wood from Grassy Mountain Vale also has much to tell about the
Eastern Oregon paleoclimate. Though the dry, seasonal Eastern Oregon climate was
about the same when this fossil was formed, petrified wood is capable of showing
important trends about the climate. By examining this piece, one can see that the tree
rings reflect seasonal temperature changes. It is also likely an oak – oak trees do not grow
in moist areas, so we can deduct that this area was about as dry as it is today 12 million
years ago. One can even estimate the region’s Milankovitch cycles in relation to climate
change. Milankovitch cycles rationalize climate and seasonal change on an astronomical
scale. The position of earth in relation to other planets (like massive Jupiter) could result
in a slight gravitational pull, varying the earth’s orbit about the sun ever so slighty.
Expert in geology and climate, Jaime Goode, says this small adjustment could make
winter colder, summer hotter, vice versa, or “even affect when seasons occur” (Goode).
So the distance between tree rings correlate to the temperature of the year, scientists can
estimate the positions of planets millions of years ago – especially if the rings are
distinctly visible – and of course, confirm their findings by consulting other disciplines.
Scientists similarly scrutinize the variety of petrified species (Carpenter). Some fossilized
wood from Eastern Oregon dating before the Miocene Epoch are trees that only grow in
warm, tropical climates – they cannot handle freezing temperatures – supporting the
theory that large Pacific islands collided with the North American mainland, creating the
Washington, Oregon, and Californian west coast (Carpenter). Before the Pacific and Juan
de fucca plates met, Eastern Oregon was beach-front property, allowing for such a wet
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climate. The Petrified Forest in Arizona, another example, was also once a humid and
moist climate – probably due to a vastly different tectonic position about 200 million
years ago. These small details prove immensely important in analyzing past climates.
Petrified wood from any area can even reveal much about a region’s ecological
history. Daniels recorded that “[a] 1962 study [near the Oregon/Idaho border] identified
fossilized remains of trees representing sixty-seven species,” ranging from common
varieties common in the east coast area to the Ginko and Metasequoia (13). This evidence
proves that Eastern Oregon once had very diverse vegetation; now it basically supports a
variety of weeds. Carpenter explains that the variety of trees and their position can also
reveal the elevation if a lake or stream was nearby. For instance, sycamores thrive near
water, so a petrified sycamore indicates the existence of a long gone body of water; on
the other hand, oaks and pines cannot live too near bodies of water and prefer dryer areas,
so this fossilized oak reveals the absence of water when it was petrified. Tree variety also
indicates a region’s elevation because each species is restricted to a certain elevation
level: if a petrified birch tree is discovered high upon a mountain, we can deduce that the
birch was petrified before the mountain formed and altered the ecosystem. Petrified tree
resin also can preserve insects. Tropical bugs have been found in fossilized sap from very
cold regions, suggesting that at one time, such a place had a much warmer climate.
Petrified tree pollen, usually found in lake beds, also can indicate the kind of trees and
vegetation that thrived in areas where fossils are scarce. Nature inscribed its history in
petrified wood, and speaking the language allows us to make connections to the world’s
evolution.
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The value of petrified wood explains the story of people. Many Native Americans
used petrified wood to create arrowheads and spearheads, making hunting and warfare
more effective. It was also shaped into game balls, tools, and used for building materials.
Some tribes also cherished spiritual legends relating to the rock. For instance, the Navajo
believed the logs in what is now Petrified Forest National Park to be the bones of the evil
monster-god, Yeitso, who was defeated in an epic lightning battle (6, Daniels). Yeitso
was the offspring of Tsohanoai (the sun god) and Naste Estsan (the spider goddess who
taught humans how to weave), and was the chief of the Anaye – a race of giant
bloodthirsty monsters who were born from “unnatural sex acts” between either gods and
human women, Yeitso and his mother, or as a result of lonely women impaling
themselves with odd objects (6). Though there are many variations of the legend of
Yeitso’s defeat, the common story explains many natural processes (like the sun’s cycle),
how many animal and plant species came about, how precious stones were dispersed, and
even encourages bravery and courage in warfare (6). The Paiute peoples believed that the
Petrified Forest in Arizona was a battle site between “the Thunder God Shinauave and his
enemies,” and that the petrified logs “were spent arrow shafts and spears” (Daniels, 7).
Petrified wood was/is also made into beads to make jewelry, and jewelry was, and
still is in many places, a form of currency. Beautiful gems like this art piece were created
through natural processes, and artisans continued the ancient tradition begun by the earth,
and refined the stones into polished accessories. Petrified wood has wedged itself into
human culture through this art. But petrified wood was also important to famous
European thinkers. According to Daniels, “Leonardo Divinci…used his knowledge of
[petrified wood] in developing theories regarding the formation of the earth,” and Darwin
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used it as evidence to support his evolution theory in relation to landscapes (7-9). The
idea of evolution is not a new concept, and understanding petrified wood has allowed
thinkers to look into the past and question the origins of the world hundreds of years ago.
After examining the chemical, geological, environmental, cultural, and historical
story behind petrified wood, it is clear that this is more than a simple rock. Understanding
the formation process of this fossilized specimen is key to unlocking the secrets of the
natural past, which is important in rationalizing present happenings. Petrified wood
pieces are the most important evidence in determining “when did this mountain get here,
was there a lake that was buried by lava, how diverse was the ecosystem at one given
period” etc. And this specific piece, probably oak, leads to complex explanations of
paleo-Oregon: this tree did not live near a body of water; the landscape sustained more
than just weeds; stress beneath the earth and multiple volcanic eruptions reformed the
landscape over and over again. Petrified wood embodies natural change because it
reflects the continuous evolution of the land; death, because the tree suddenly,
unexpectedly died one day; immortality, as the specimen was preserved and is admired
millions of years after it’s death; beauty, and wisdom.
Emry states that “the value of a petrified wood specimen depends on the quality
of preservation, the clarity, size, what is known about the piece, and the beholder.” A
clear specimen lends itself to be identified as a species and has sharply preserved cells
and growth rings. Knowing where the specimen was found is also important to the value:
“the better story you can tell about it, the more it’s worth” (Carpenter). This includes
scientific and monetary value. A collector might value a piece more from Montana than
Eastern Oregon; a jeweler might pay more for an colorful specimen, while a geologist is
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more interested in the wood-like piece that holds knowledge. Size is also important, as a
larger specimen is much more rare than a pebble-sized one. In geology, no specimen is
quite like the other; each is unique, so each is worth collecting (Emry).
Perhaps petrified wood holds personal value as well. When looking at this
petrified specimen, I see myself. Its home was in Eastern Oregon, not far from where I
grew up; I see my great-grandfather who collected precious rocks and petrified wood,
leaving much of his collection to me; I see the beautiful volcanic formations that I
journey through from my home to Caldwell; I see simple beauty, structure, and rigidity –
like my personality. This piece is a reflection of myself. What if every tree fossil is a
picture of an individual: could petrified wood universally be the looking glass to
humanity?
Petrified wood is valuable, not only because it is a result of a rare chemical
process, but because of the knowledge it holds. Secrets about the environment in days
long before humans, cultural monuments, and the formation of the earth are imbedded
within the wood’s crystalline structure. Petrified wood forces us to question the origins of
the earth and prompts us to investigate the development of the earth and how it is
changing. It reveals to us new chemical processes that drive environmental change in
landscapes and organisms. This petrified wood specimen acts as a reminder of how an
ancient opalized rock has molded world history. Petrified wood is a tangible idea that was
born before the scope of human existence. Beholding this object is beholding our
imagination: its journey encompasses factors that are only limited by our minds.
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Works Cited
Carpenter, Nathan E. Meeting interview. 30 Nov. 2016.
Cummings, Michael. “Stratigraphic and Structural Evolution of the Middle Miocene
Synvolcanic Oregon-Idaho Graben.” Geological Society of America Bulletin.
May, 2000. 21 Nov. 2016.
<https://www.researchgate.net/profile/Michael_Cummings6/publication/2799465
70_Stratigraphic_and_structural_evolution_of_the_middle_Miocene_synvolcanic
_Oregon-Idaho_graben/links/55ce530308ae6a8813849e26.pdf>
Daniels, Frank J. “Petrified Wood: The World of Fossilized Wood, Cones, Ferns, and
Cyads.” First Edition. Western Colorado Publishing Co, 1998.
Emry, Howard. Meeting interview. 30 Nov. 2016.
Goode, Jaime. Meeting interview. 21 Nov. 2016.
Haris, Stephen L. “Fire Mountains of the West: The Cascade and Mono Lake
Volcanoes.” Mountain Press Publishing Co, 1988.
Tormey, Nathan. Meeting Interview. 18 Nov. 2016.
Wozniak, Edward and Balladeer. “Navajo Myth (Clear).” Glitternight. 2010-2012. 25
Nov. 2016. <https://glitternight.com/navajo-myth-clear/>