The father-daughter duo from the Cowboy State didn’t know it at the time, but the large boulder they found is a huge 2.5 billion-year-old discovery and a unique find for Wyoming hunters.
The dimensional rock found by Laramie resident Patrick Corcoran and his daughter Cora is called Banded Iron Formation. It comes from an important moment in Earth’s history, originating in the ancient oceans that covered Wyoming more than 2.5 billion years ago.
“I’ve never seen one this big in all 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 dedicated 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 bands formed over millions of years of sedimentary compression. For the uninitiated, it could be mistaken for a giant piece of petrified wood.
Rusting oceans
Banded iron formations are unique sedimentary rocks that formed more than 2 billion years ago. The formation got its name from the distinctly colored layers prominently visible in the boulder found by Corcorany.
“It consists 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.
Alternating bands of hematite and hornblende record an important chapter in Earth’s history. Banded iron 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 was very poor in oxygen and the oceans had no dissolved oxygen,” she said. “When photosynthetic cyanobacteria started to evolve and pump oxygen into the ocean and atmosphere, it basically rusted the oceans.”
Because iron does not dissolve in water, any rust floating in the ocean settled to the sea floor, forming thin but widespread banded iron formations. The reddish color of the UW sample comes from 2 billion-year-old rust created by cyanobacteria oxygenating the oceans and atmosphere that make our planet habitable today.
Paving 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 are not easy to get to and there are not many of them.
Most of Wyoming’s banded iron formations are exposed at the highest points of the mountain range, inaccessible to all but the most hardy climbers. And there is little interest in getting into these deposits because banded iron formations are not an economically viable resource.
The Corcorans found their 2-billion-year-old boulder on a flat, private ranch with not a mountain in sight. Vietti classified their find as cobblestones caused by a wet descent from a mountain exposure.
“Outwash cobblestones were picked up from the mountains by streams or glaciers,” she said, “and fell down from the mountains and deposited on the plains of Wyoming. You find them when you walk the prairies. That’s where most of our banded iron comes from.”
The rolling of water and ice rounded and smoothed the boulder’s jagged edges, revealing dramatically colored layers. It’s the perfect piece for the UW Museum of Geology, and they’ve already found the perfect spot for it.
Bigger Is Better (Outside)
The UW Museum of Geology has several specimens from banded iron formations collected in Wyoming. The two small pieces will be displayed in “Wyoming’s Oceans,” a new exhibit at the museum that showcases Wyoming’s watery past while highlighting the collections and research of the university’s past and present biologists, geologists and paleontologists.
The Banded Iron Boulder of the Corcorans is notable for its size. Vietti said it is the largest Wyoming specimen she has seen in her career.
“Most of the banded iron pavers you get in Wyoming are between the size of a thimble 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-fridge and much heavier. Since the “Wyoming’s Oceans” design has already been completed, the Corcoran Banded Iron Boulder is too large and too late to be included in the new exhibit.
Vietti envisioned an academic future for the acquisition.
“It will be a show specimen, but mostly outside for now,” she said. “We’ll have a sign or some kind of label for it for the general public. And it will be used as a teaching specimen for our Intro to Geology labs (at the UW.).”
Patrick and Cora Corcoran are excited that their big boulder has a bright future ahead of them, no matter where it is. 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 don’t have room for it in the museum right now. Maybe we’ll put it inside in the future, but I think it’ll be fun outside for now. And we’re very happy to have it there.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.