The rocks of the Grand Canyon Supergroup are between 1.2 billion and 2.0 billion years old. This places them firmly within the Proterozoic Eon, specifically the Paleoproterozoic Era (2.5 billion to 1.6 billion years ago) and the Mesoproterozoic Era (1.6 billion to 1 billion years ago).

Here's a breakdown of the geological time scale and where the Grand Canyon Supergroup fits in:

* Eon: Precambrian (4.5 billion to 541 million years ago)

* Era: Proterozoic (2.5 billion to 541 million years ago)

* Period: Paleoproterozoic (2.5 billion to 1.6 billion years ago) - Grand Canyon Supergroup Rocks (1.2 to 2.0 billion years old)

* Period: Mesoproterozoic (1.6 billion to 1 billion years ago) - Grand Canyon Supergroup Rocks (1.2 to 2.0 billion years ago)

* Era: Archean (4.0 billion to 2.5 billion years ago)

* Era: Hadean (4.5 billion to 4.0 billion years ago)

* Eon: Phanerozoic (541 million years ago to present)

* Era: Paleozoic (541 to 252 million years ago)

* Era: Mesozoic (252 to 66 million years ago)

* Era: Cenozoic (66 million years ago to present)

It's important to note that the Grand Canyon Supergroup is made up of multiple layers of rock deposited over a long period. The age of the oldest rock layers at the bottom of the Supergroup is around 2.0 billion years, while the youngest layers at the top are about 1.2 billion years old.

The Grand Canyon Supergroup is a truly ancient geological formation, offering a glimpse into a period of Earth's history when life was still in its early stages.