What is relative dating

New rock layers are always deposited on top of existing rock layers.

Therefore, deeper layers must be older than layers closer to the surface. You can see an example in Figure below and at the link below.[Link about law of superposition here.] Rock layers extend laterally, or out to the sides.

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The matching rock layers were deposited at the same time, so they are the same age.

Sediments were deposited in ancient seas in horizontal, or flat, layers.

If sedimentary rock layers are tilted, they must have moved after they were deposited.

In history, archeology and science, the process of dating discoveries helps provide important information about the find.

Dating a fossil, for example, can help scientists learn more about where the discovered creature fit into evolution or can assist them in identifying the specimen.

Science uses relative and radioactive dating to determine the age of these discoveries, but these two methods are different.

The way things happen now is the same way things happened in the past. Mountains grow and mountains slowly wear away, just as they did billions of years ago. They become extinct, meaning that they die out completely. They use clues from rocks and fossils to figure out the order of events.

As the environment changes, living creatures adapt. They think about how long it took for those events to happen. The laws of stratigraphy can help scientists understand Earth’s past. Refer to the figure as you read about the laws below.

The laws of stratigraphy are usually credited to a geologist from Denmark named Nicolas Steno. Superposition refers to the position of rock layers and their relative ages.

Relative age means age in comparison with other rocks, either younger or older.

The relative ages of rocks are important for understanding Earth’s history.

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