Relative age dating animation radiometric dating exam questions
To create the geologic time scale, geologists correlated rock layers.
Steno's laws were used to determine the relative ages of rocks.
He realized that for both to occur would take an extremely long time. What evidence is used to match rock layers in different places? They may be found on more than one continent or in more than one country.
This made him realize that Earth must be much older than people thought. It meant there was enough time for life to evolve gradually. [Insert a link to a video or animation about Hutton’s unconformity.] When rock layers are in the same place, it’s easy to give them relative ages. For example, the famous White Cliffs of Dover are on the coast of southeastern England.
Rock layers may have another rock cutting across them, like the igneous rock in Figure below. To determine this, we use the law of cross-cutting relationships.
The cut rock layers are older than the rock that cuts across them.
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.
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.Erosion may have worn away some of the rock, but layers on either side of eroded areas will still “match up.” Look at the Grand Canyon in Figure below. You can clearly see the same rock layers on opposite sides of the canyon.The matching rock layers were deposited at the same time, so they are the same age.Hutton's discovery was a very important event in geology!Hutton determined that the rocks were deposited over time. Hutton knew that deposition and erosion are very slow.
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The relative ages of rocks are important for understanding Earth’s history.