First, that the Grand Canyon ... So those layers of rock are really a bit like the rings on a section of a tree trunk. Both giving a visible indication of how old they are. Download/print a ...

Peak and her colleagues looked at the rock layers right under (and thus older than) the Great Unconformity from eight t locations in the Grand Canyon to find out when the rock above was swept away.

To peer into the Grand Canyon is to behold, in its rock layers, a record of Earth’s distant past. The oldest layers at the bottom date back more than 1.5 billion years. It is some of the most ...