Not only is the Morton Gneiss of Minnesota absolutely gorgeous, it’s also really freaking old. Zircon crystals in the gneiss have been dated to ~3.6 Ga [that’s 3.6 billion years old!]
At their age, these rocks are from the Archean Eon, the second eon in Earth’s history (the Hadean is the first), which lasted from 4.0 – 2.5 Ga
This rock is the second oldest terrestrial rock I’ve ever seen, with the Acasta Gneiss being the oldest that I’ve seen (and the very oldest that exists).
To read a little bit about the Acasta Gneiss, the oldest rock on Earth at 4.0 Ga, click HERE
Image by author
Emily Zawacki, Ph.D. 