A father-daughter duo from the Cowboy State didn’t know it at the time, but the big rock they found is a huge discovery that’s 2.5 billion years old and a unique find for Wyoming rock hunters.
The large stone found by Laramie resident Patrick Corcoran and his daughter Cora is called a banded iron formation. It comes from an important time in Earth’s history, as it formed in the ancient oceans that covered Wyoming more than 2.5 billion years ago.
“I’ve never seen one this big in my time in Wyoming,” said Dr. Laura Vietti, director of the geological museum and collections at the University of Wyoming, where the Corcorans donated their find. “It’s really helpful to have museum supporters like Patrick and Cora because they were able to find this rare specimen and bring it to us.”
The large, reddish, relatively smooth and shiny rock certainly stands out, with clearly visible bands formed over millions of years of sedimentary compression. For those who don’t recognize it at first glance, it could be mistaken for a giant piece of petrified wood.
Rusting the oceans
Banded iron formations are unique sedimentary rocks that formed more than 2 billion years ago. The formation gets its name from the layers of different colors, strikingly visible in the rock found by the Corcorans.
“It’s made up of alternating layers of a shiny metal, usually hematite, and a red flint that alternates over and over again,” Vietti said. “And that’s why it’s called iron banding.”
Alternating bands of hematite and chert tell an important chapter in Earth’s history. Iron band formations are the earliest evidence of oxygen in the oceans and form the basis of multicellular life on the planet.
“Before multicellular life evolved on Earth, the atmosphere had very little oxygen and the oceans had no dissolved oxygen,” he said. “When photosynthetic cyanobacteria began to evolve and pump oxygen into the ocean and atmosphere, they essentially oxidized the oceans.”
Since iron does not dissolve in water, all the rust floating in the ocean settled on the seafloor and formed thin but widespread banded formations of iron. The UW specimen’s reddish color comes from 2 billion-year-old rust created by cyanobacteria that oxygenate the oceans and atmosphere and make our planet habitable today.
This huge piece of banded iron rock is a unique discovery in Wyoming by Laramie resident Patrick Corcoran and his daughter, Cora. It is now on display at the University of Wyoming Geological Museum. (University of Wyoming Geological Museum)
Going forward
Banded iron formations can be found on every continent on Earth, including Wyoming. But that doesn’t mean they are easy to find and are often not found in the condition of the jeans.
“We have the right rock age and the right depositional environments to form banded iron formations,” Vietti said. “But it’s not easy to get to them and there aren’t many of them.”
Most of Wyoming’s banded iron formations are exposed at the highest points of mountain ranges, inaccessible to all but the most tenacious climbers. And there is little interest in reaching those deposits since banded iron formations are not an economically viable resource.
The Corcorans found their 2 billion-year-old rock on the flat expanse of a private ranch with no mountains in sight. Vietti classified his discovery as a cobblestone that came down wet from a mountain exposure.
“The cobblestones were captured from the mountains by streams or glaciers,” he said, “and fell down the mountains and were deposited on the plains of Wyoming. You’ll find them as you walk across the prairie. That’s where most of our iron bands.”
As it fell through the water and ice, the jagged edges of the rock were rounded and smoothed, revealing layers of dramatic colors. It is a perfect piece for the University of Washington Geological Museum and it has already found a perfect place for it.
This huge chunk of banded iron rock is a unique discovery in Wyoming by Laramie resident Patrick Corcoran and his daughter, Cora. It is now on display at the University of Wyoming Geological Museum. (University of Wyoming Geological Museum)
The bigger the better (outside)
The Geological Museum at the University of Washington has several specimens of banded iron formations collected in Wyoming. Two small pieces will be featured in “Wyoming’s Oceans,” a new exhibit at the museum that showcases Wyoming’s aquatic past while highlighting the collections and research of the university’s past and present biologists, geologists and paleontologists .
The Corcorans iron-banded rock is significant for its size. Vietti said it is the largest Wyoming specimen he has seen in his career.
“Most iron banding cobbles found in Wyoming are between the size of a thimble and a grapefruit,” he said. “This particular specimen is really important because it is very large and shows the unique banded iron layers very well.”
This Wyoming banded iron specimen is a little smaller than a mini refrigerator and much heavier. Since the design for “Wyoming Oceans” has already been finalized, Corcoran’s iron-banded rock is too big, too late to be included in the new exhibit.
Vietti envisioned an academic future for the acquisition.
“It’s going to be a display specimen, but for now mainly outside,” he said. “We will have a sign or some label attached for the general public. And it will be used as a teaching sample for our Introductory Geology labs (at the University of Washington).”
Patrick and Cora Corcoran are thrilled that their big rock has a promising future ahead of it, regardless of its location. It has survived two billion years of Wyoming’s geological history, so it should have no problem withstanding the natural forces of a college campus.
“It’s tremendously heavy and tremendously big,” Vietti said. “We don’t really have room for it in the museum right now. We may put it inside in the future, but I think for now it’ll be happy outside. And we’re very happy to have it there.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
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