Specifically, the oldest fossils are found in the Vishnu Schist, which is a layer of metamorphic rock at the very bottom of the canyon. These fossils are incredibly old, dating back to the Precambrian era, over 540 million years ago.
While these fossils are incredibly ancient, they are also very rare and difficult to find. The Vishnu Schist is heavily metamorphosed, which means the original fossils have been significantly altered by heat and pressure.
It's important to note that the Grand Canyon is a treasure trove of fossils, with different layers containing different fossils from various eras. However, the oldest fossils reside in the very bottom of the canyon's depths.
