A new discovery by geologists has changed perceptions about the oldest rock in the United States.
According to research published in GSA Today, the title now belongs to the Watersmeet gneiss in Michigan, which is at least 3.6 billion years old, instead of the Morton gneiss in Minnesota as previously thought.
For decades, a sign has stood proudly in the Minnesota River Valley that reads, "The Oldest Rock in the World ."
This plaque, erected in 1975, marks the site of a gneiss believed to be 3.8 billion years old. However, recent research by a team of scientists led by Carol Frost has shown that this figure may be exaggerated by at least 300 million years.
The story began with a casual conversation between geologists. Professor Bob Stern of the University of Texas at Dallas and graduate student Clinton Crowley initiated the discussion, and they then sought the help of experts in ancient rock dating, including Frost.
Determining the age of rocks isn’t as simple as many people think. When geologists date rocks, they’re actually dating the minerals that make up the rock, says Frost of the University of Wyoming. It’s like trying to determine the age of a building by analyzing individual bricks—not all of them are the same age.
Zircon is often the mineral of choice for scientists when dating rocks. However, its durability – its ability to withstand weathering, high temperatures and pressures – means it often outlasts the host rock.
After crystallization in magma, zircon crystals may be swept into sediments or crushed by tectonic forces, forming new rock but possibly distorting the age of the crystals.
The team sampled gneiss from three regions: Minnesota, Wyoming, and Michigan. Analysis showed that the Watersmeet gneiss in Michigan is between 3.8 billion and 1.3 billion years old, with signs of a turbulent past: volcanic intrusion, metamorphism, and tectonic activity.
Based on the evidence collected, scientists have determined its minimum age to be 3.6 billion years.
The significance of this research goes beyond setting a record. Jeffrey Vervoort, a geologist at Washington State University who was not involved in the study, stressed that understanding the exact age of ancient rocks helps scientists reconstruct Earth's history more accurately, from the time life began to the rise of mountains and climate change.
Although the Watersmeet gneiss currently holds the title of "oldest rock in America," scientists believe that even older rocks may exist.
3.8 billion-year-old zircon crystals found in gneiss in Michigan and Wyoming suggest the existence of older rocks that may have been recycled in the Earth's mantle or are still buried deep in the Earth's crust./.
Source: https://www.vietnamplus.vn/tang-da-36-ty-nam-tuoi-o-my-dat-ky-luc-tang-da-lau-doi-nhat-the-gioi-post1035290.vnp
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