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This means that the remains of living things are useful for carbon-14 dating.
Most rocks, however, are not useful for carbon-14 dating (either not enough carbon, or didn't derive its carbon from the atmosphere-shallow water reservoir).
Refer to the geologic time scale on page 219 for the names of each of the geologic time periods, as well as the absolute dates attached to each Period. Four major unconformities are evident in the Grand Canyon cross-section.
As geologists piece together the information at various outcrops, they can begin to assemble a "geologic map" (like a road map) of an entire region (consisting of many square miles).
Thus, carbon-14 is of no use in determining the absolute ages of, for example, dinosaur fossils.
The only materials that start out with usable amounts of carbon-14 in them are carbon-bearing materials which derived their carbon immediately from the atmosphere or from shallow water.
View the above image, a cross-section (side-view of a cut-out through the crust) of the Grand Canyon.
Study this diagram carefully, noting the orientation of individual rock layers, as well as the type of rock in each layer, and the age of the rock in each layer. IS TO CLEARLY IDENTIFY FOUR MAJOR UNCONFORMITIES IN THE GRAND CANYON SEQUENCE.