The Cowboy State father and daughter duo didn’t know it at the time, but the large rock they found was a huge find that was 2.5 billion years old and a one-of-a-kind find for Wyoming rock hounds.
The huge rock discovered by Laramie resident Patrick Corcoran and his daughter Cora is called Band Iron. It is from an important moment in Earth’s history, 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, manager 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 rock certainly stands out, reddish in color and relatively smooth and shiny with clearly visible striations formed over millions of years of sedimentary compression. To those who don’t know it at first glance, it could be mistaken for a gigantic piece of petrified wood.
Rusting of the oceans
Banded iron formations are unique sedimentary rocks that formed more than 2 billion years ago. The formation gets its name from the distinctly colored layers strikingly visible in the stone discovered by the Corcorans.
“It’s made up of alternating layers of a sparkling metal, usually hematite, and a red chert that alternates over and over again,” Vietti said. “And that’s why it’s called a banded iron formation.”
The alternating bands of hematite and shingle describe an important chapter in Earth’s history. Banded iron formations are the earliest evidence of oxygen in the oceans, forming the basis for multicellular life on the planet.
“Before multicellular life developed on Earth, the atmosphere was very low in oxygen and the oceans had no dissolved oxygen,” she said. “When photosynthetic cyanobacteria began to evolve and pump oxygen into the ocean and atmosphere, it essentially rusted the oceans.”
Since iron does not dissolve in water, all the rust floating in the ocean settles to the sea floor and forms thin but widespread banded iron formations. The reddish color of the UW specimen comes from 2-billion-year-old rust created by cyanobacteria saturated with oxygen in the oceans and atmosphere that make our planet habitable today.
Cobble Along
Banded iron formations can be found on every continent on Earth, including Wyoming. But that doesn’t mean they’re easy to find, and they’re often not in the Cowboy State.
“We have the right rock age and the right depositional environment to form banded iron formations,” Vietti said. “But they’re not easy to get to, 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 most but the most determined climbers. And there is little interest in getting to these deposits because banded iron formations are not an economically viable resource.
The Corcorans found their 2-billion-year-old stone in the plains of a private ranch where not even a mountain could be seen. Vietti classifies their find as a cobblestone that makes a wet descent from a mountain exposure.
“The washout debris was picked up from the mountains by streams or glaciers,” she said, “and fell down the mountains and deposited on the plains of Wyoming. You will find them as you walk around the prairie. most of our strip iron comes from.”
Rolling through water and ice rounded and smoothed the jagged edges of the stone, revealing the dramatically colored layers. It’s the perfect piece for the UW Museum of Geology, and the perfect location for it has already been found.
Bigger is better (outside)
The UW Museum of Geology has several specimens of banded iron formations collected in Wyoming. Two small pieces will be featured in “Oceans of Wyoming,” a new exhibit at the museum showcasing Wyoming’s aquatic past while highlighting the collections and research of the university’s past and present biologists, geologists and paleontologists.
The Corcoran banded ironstone is significant because of its size. Vietti said it was the largest Wyoming specimen she had seen in her career.
“Most of the banded iron cobbles you get in Wyoming are between the size of a foxglove and a grapefruit,” she said. “This particular specimen is really important because it is so large and shows the unique banded iron layers very well.”
This specimen of Wyoming band iron is slightly smaller than a mini-refrigerator and much heavier. With the Oceans of Wyoming design now finalized, Corcoran’s banded ironstone is too big and too late to the party to be included in the new exhibit.
Vietti envisioned an academic future for the acquisition.
“It will be a showpiece, but mostly outside for now,” she said. “We will have a sign or some sort of tag attached to it for the general public. And it will be used as a teaching model for our Intro to Geology labs (at the UW.)’
Patrick and Cora Corcoran are excited that their large rock has a promising future ahead of it, regardless of its location. It has survived two billion years of Wyoming’s geologic history, so it should have no problem withstanding the natural forces of a college campus.
“It’s awfully heavy and awfully big,” Vietti said. “We really don’t have room for it in the museum right now. We may put him inside in the future, but I think he’ll be happy outside for now. And we’re very happy to have him there.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
