Start Radiometric dating rock samples

Radiometric dating rock samples

When we look at sand in an hourglass, we can estimate how much time has passed based on the amount of sand that has fallen to the bottom.

Relative age dating also means paying attention to crosscutting relationships.

Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.

To date a radioactive rock, geologists first measure the “sand grains” in the top glass bowl (the parent radioisotope, such as uranium-238 or potassium-40).

They also measure the sand grains in the bottom bowl (the daughter isotope, such as lead-206 or argon-40, respectively).

However, rocks and other objects in nature do not give off such obvious clues about how long they have been around.

So, we rely on radiometric dating to calculate their ages.

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.

Radiometric dating, or radioactive dating as it is sometimes called, is a method used to date rocks and other objects based on the known decay rate of radioactive isotopes.

Different methods of radiometric dating can be used to estimate the age of a variety of natural and even man-made materials.

Part 2 explains how scientists run into problems when they make assumptions about what happened .