Dating of rock layers
Imagine that you're a geologist, studying the amazing rock formations of the Grand Canyon.Your goal is to study the smooth, parallel layers of rock to learn how the land built up over geologic time.Now imagine that you come upon a formation like this: What do you think of it? How can you make any conclusions about rock layers that make such a crazy arrangement?
Once we assume that all rock layers were originally horizontal, we can make another assumption: that the oldest rock layers are furthest toward the bottom, and the youngest rock layers are closest to the top. The forest layer is younger than the mud layer, right? When scientists look at sedimentary rock strata, they essentially see a timeline stretching backwards through history.Plus, get practice tests, quizzes, and personalized coaching to help you succeed.Free 5-day trial Discover how geologists study the layers in sedimentary rock to establish relative age.Changes in the environment cause changes in the rocks. Sometimes, the layers are twisted or tilted because of the movement of the Earth’s tectonic plates. Scientists study these layers to learn more about the Earth’s history.For example, a volcanic eruption may create a layer made of hardened ash. Radiometric dating measures radioactive elements in the rocks.
The highest layers tell them what happened more recently, and the lowest layers tell them what happened longer ago.