The layers of rock at the base of the canyon were deposited first, and are thus older than the layers of rock exposed at the top (principle of superposition).
In the Grand Canyon, the layers of strata are nearly horizontal.
These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth's surface is moving and changing.
As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.
Younger layers are deposited on top of older layers (principle of superposition).In addition to being tilted horizontally, the layers have been faulted (dashed lines on figure).Applying the principle of cross-cutting relationships, this fault that offsets the layers of rock must have occurred after the strata were deposited." First, the relative age of a fossil can be determined.Relative dating puts geologic events in chronological order without requiring that a specific numerical age be assigned to each event.