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.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.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.
By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time.
The age of the fossil must be determined so it can be compared to other fossil species from the same time period.
Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.
Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.
Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.
Search for chronological dating:
A fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved.