Method of dating ancient remains

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.

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.

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.

This is the principle of cross-cutting relationships.

The principle states that any geologic features that cut across strata must have formed after the rocks they cut through (Figures 2 and 3).

According to the principle of original horizontality, these strata must have been deposited horizontally and then titled vertically after they were deposited.

A fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved.

However, by itself a fossil has little meaning unless it is placed within some context.

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