Let's say we find out, through numerical dating, that the rock layer shown above is 70 million years old.
We're not so sure about the next layer down, but the one below it is 100 million years old. Not exactly, but we do know that it's somewhere between 70 and 100 million years old.
Geologists establish the age of rocks in two ways: numerical dating and relative dating.
Numerical dating determines the actual ages of rocks through the study of radioactive decay.
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distinctions between relative-age and absolute-age measurements. As the name implies, relative dating can tell which of the two artifacts is older. However, there are radiometric dating methods that can be used on sedimentary rock, including luminescence dating.Isotopes are important to geologists because each radioactive element decays at a constant rate, which is unique to that element. Relative value is value compared to some arbitrary other value.At the same time, it has significance as people may be able to understand the order and then decode the era. The table below shows characteristics of some common radiometric dating methods.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.The highest layers tell them what happened more recently, and the lowest layers tell them what happened longer ago.