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.

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However, the age of each fossil primate needs to be determined so that fossils of the same age found in different parts of the world and fossils of different ages can be compared.

There are three general approaches that allow scientists to date geological materials and answer the question: "How old is this fossil?

The principle of superposition states that in an undeformed sequence of sedimentary rocks, each layer of rock is older than the one above it and younger than the one below it (Figures 1 and 2).

Accordingly, the oldest rocks in a sequence are at the bottom and the youngest rocks are at the top.

" 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.Third, magnetism in rocks can be used to estimate the age of a fossil site.This method uses the orientation of the Earth's magnetic field, which has changed through time, to determine ages for fossils and rocks.The study of strata is called stratigraphy, and using a few basic principles, it is possible to work out the relative ages of rocks.Just as when they were deposited, the strata are mostly horizontal (principle of original horizontality).Layers that cut across other layers are younger than the layers they cut through (principle of cross-cutting relationships).