Example of relative dating methods
To determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones. This rule is common sense, but it serves as a powerful reference point.Geologists draw on it and other basic principles ( to determine the relative ages of rocks or features such as faults.Pretty obvious that the dike came after the rocks it cuts through, right?With absolute age dating, you get a real age in actual years.On the other hand, the half-life of the isotope potassium 40 as it decays to argon is 1.26 billion years.
Absolute age dating: Have students work alone or in pairs to find an article or paper that uses radiometric age dating.Like the other kind of dating, geologic dating isn’t always simple.Activity: Further discussion: Good overview as relates to the Grand Canyon: age dating: Use with this cross section of the Grand Canyon from the USGS’s teaching page: Canyon Have students reconstruct a simple geologic history — which are the oldest rocks shown? Are there any that you can’t tell using the Rule of Superposition?In a way this field, called geochronology, is some of the purest detective work earth scientists do.There are two basic approaches: relative age dating, and absolute age dating.