Three rules of relative dating

This means that a quartz sandstone deposited 500 million years ago will look very similar to a quartz sandstone deposited 50 years ago.

With this in mind geologist have long known that the deeper a sedimentary rock layer is the older it is, but how old?

Although there might be some mineral differences due to the difference in source rock, most sedimentary rock deposited year after year look very similar to one another.

Throughout the history of life, different organisms have appeared, flourished and become extinct.

Many of these organisms have left their remains as fossils in sedimentary rocks.

The secondary rocks were thought to include interlayered basalts, which Werner thought formed by combustion of buried coal layers.

The Scottish geologist James Hutton (1726-1797) argued that granite and basalt by solidification within the earth (as opposed to precipitating in from oceanwater).

This idea is known as Plutonism, in reference to the God of the deep underworld.

Hutton viewed tilted strata as having been initially deposited horizontally, and then were subsequently deformed (tilted and folded) by the forces of Earth's internal heat engine.

The same thing can be done with geologic features in a rock outcrop.

To do this geologists use the Laws of Relative Dating.

Often when geologists examine rock outcrops like the one illustrated above they are interested in not only the types of rocks present, but the order in which they formed.

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