Geologists recently dated the age of Watersmeet gneiss, a type of rock in the Upper Peninsula, as the oldest in the U.S. Here ...

A weathered sign in the Minnesota River Valley proudly proclaims: “World’s Oldest Rock.” Erected in 1975, it marks a 3.8-billion-year-old gneiss — or so scientists thought.

Lewisian gneiss is metamorphic rock, which means it was formed by being heated up and ... After some consideration, the team select a rock weighing six to seven tonnes. “It has lovely banded patterns ...