Dating relative rock
The tilted rocks at the bottom are part of the Proterozoic Grand Canyon Group (aged 825 to 1,250 Ma).The flat-lying rocks at the top are Paleozoic (540 to 250 Ma).The lava flow took place some time after the diorite cooled, was uplifted, and then eroded.(Hammerhead for scale) [SE]Figure 8.6b Rip-up clasts of shale embedded in Gabriola Formation sandstone, Gabriola Island, B. The pieces of shale were eroded as the sandstone was deposited, so the shale is older than the sandstone.Recognizing unconformities is important for understanding time relationships in sedimentary sequences.An example of an unconformity is shown in Figure 8.8.CC BY-SA 3.0], via Wikimedia Commons' src=" alt="The canyon is shown with many layers" width="3600" height="2400" srcset=" sizes="(max-width: 709px) 85vw, (max-width: 909px) 67vw, (max-width: 1362px) 62vw, 840px"/The geologic time scale and basic outline of Earth’s history were worked out long before we had any scientific means of assigning numerical age units, like years, to events of Earth history.
Known for the diversification and evolution of life, along with the formation of Pangea.
The lower sandstone layer is disrupted by two faults, so we can infer that the faults are younger than that layer.
But the faults do not appear to continue into the coal seam, and they certainly do not continue into the upper sandstone.
Using this time scale, geologists can place all events of Earth history in order without ever knowing their numerical ages.
The specific events within Earth history are discussed in Chapter 8.
Search for dating relative rock:
Tilting and erosion of the older rocks took place during this time, and if there was any deposition going on in this area, the evidence of it is now gone.