Recent studies have upended long-held ideas about the age of some of these oldest rocks, particularly in the United States. Our analysis Carol Frost of the University of Wyoming and her team conducted an illuminating study. They found that Michigan’s Watersmeet Gneiss, previously considered to be younger, is at least 3.6 billion years old. This fresh discovery shows that the search for America’s oldest rock may be a trickier tale than it appears.
The team looked at minerals on eight different historical gneisses scattered around the country. To do so, they turned their attention to the Morton Gneiss in Minnesota, a formation often lauded as one of the U.S.’s oldest geological structures. The current age of the Morton Gneiss is listed as 3.8 billion years on a placard by the road adjacent to the outcrop. According to Frost, this claim is at least 300 million years too old. At the other end of the spectrum, the Morton Gneiss includes zircons that are 2.6 billion, 3.3 billion, and even 3.5 billion years old.
Though the study was primarily aimed at gneisses in Minnesota and Michigan, it showed some of the most promising results in Wyoming. Twenty-five out of every 30 zircons in Wyoming’s Sacawee Gneiss date to about 3.4 billion years ago. Nine rogue grains in this formation date back to 3.8 billion years. This find indicates that these ancient rocks have either been buried under Earth’s crust or recycled within the planet’s mantle.
Mark Harrison of UCLA observed that the results only represent rocks that can be accessed at earth’s surface. He stressed that unlike a formal docket, these findings do not establish an official precedent. Rather, they record the most ancient crustal rock formations that we can still retrieve today. “They may have documented [the United States’] oldest known rock,” Harrison stated.
The policy implications of this research raise larger questions about how scientists should re-construct Earth’s history. Frost remarked, “A rock can be composed of minerals that formed at different ages,” which complicates how age is assigned. Further research strongly suggested that the zircons found in the Sacawee Gneiss and Watersmeet Gneiss originated from two distinct parent rocks. These rocks were possibly reconstituted within a much younger, geologically active interval.
Michigan and Wyoming aren’t the only places with old geology. The Canadian Acasta Gneiss makes a claim to the title of the world’s oldest rock, said to be about 4 billion years old. That recent analysis is behind a newly sparked controversy over just how old the rock formations of North America are. Frost illustrated how this never-ending quest raises critical questions. These questions explore the geological history of Earth and the processes that have shaped our planet.
“When I give talks on the early Earth, I always finish with the Salvador Dali painting with the drooping clocks in a barren landscape,” he explained, underscoring the fluidity and complexity involved in determining geological time.
Scientists are conducting new research on these ancient structures. The research they did found illustrates the point that our understanding of Earth’s history is always changing. Each new discovery not only sheds light on the rocks themselves but on the broader narrative of how our planet has changed over billions of years.
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