Most sedimentary rocks are laid down in flat, horizontal layers. Relative dating arranges geological events – and the rocks they leave behind – in a sequence. The method of reading the order is called stratigraphy (layers of rock are called strata).Most sedimentary rocks are laid down in flat, horizontal layers. Relative dating

How rock layers are dated?

To establish the age of a rock or a fossil, researchers use some type of clock to determine the date it was formed. Geologists commonly use radiometric dating methods, based on the natural radioactive decay of certain elements such as potassium and carbon, as reliable clocks to date ancient events.

What type of rock is best for radiometric dating?

When you radiometrically date a mineral grain you are determining when it crystallized. Thus, you would like to use rocks whose crystals are roughly the same age. The easiest are igneous rocks in which all crystals are roughly the same age, having solidified at about the same time.