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The United States’ oldest known rock has existed for at least 3.6 billion years

A rock formation in Michigan has beat out other contenders for the title — for now

Photo of watersmeet Gneiss rock that could be the oldest known in the United States

An analysis of minerals in the Watersmeet Gneiss (shown) suggest the metamorphic rock dates to about 3.6 billion years ago, potentially making it the oldest known rock in the United States.

Paul Brandes

By Evan Howell

A weathered sign in the Minnesota River Valley proudly proclaims: “World’s Oldest Rock.”