Radiometric dating stuff works

Geologists have established a set of principles that can be applied to sedimentary and volcanic rocks that are exposed at the Earth's surface to determine the relative ages of geological events preserved in the rock record.

For example, in the rocks exposed in the walls of the Grand Canyon (Figure 1) there are many horizontal layers, which are called strata.

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.

Layers of rock are deposited horizontally at the bottom of a lake (principle of original horizontality).

Younger layers are deposited on top of older layers (principle of superposition).

" 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.

Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.

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 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.

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