Basement rock is the term you will often see used in reference to the Precambrian rock, the "basement of the continents." This is the rock that anchors the continents deep within the earth. The reason for this apparent dismissal of four billion years in the history of the Earth is that the farther back in time one goes, the more fragmentary the record is, and therefore the more difficult to decipher. In Wyoming, all of the Precambrian rock belongs to the oldest era of all, the Archean era, more than 2.5 billion years old. There is little evidence of significant events in late Precambrian time in Wyoming.