In order to determine the age of rocks, Geologist takes advantage of basically two techniques that differ in their process and accuracy, these are relative dating and absolute dating.
Put simply, if a geologist says to be younger than his or her colleague, that is a relative dating. If a geologist says to be 28 years old, that is an absolute dating.
Relative dating relies on a set of principles, formulated by geologists that can be applied on different types of rocks (sedimentary or volcanic) on the Earth's surface to determine the relative ages of geological events kept in rocks as a record of such events. Together with these principles, geologist uses the arrangement of rock layers to estimate the relative age of rocks with it. This process is called stratigraphy, and a branch of it, called sequenced stratigraphy seeks to determine the order or sequence in time in which rocks were laid in the available space –or accommodation in geologist terms- The principles stated before are Superposition, Faunal succession, Crosscutting relationships, and Inclusions.
It is common that geologists come across gaps in the geologic record, for which they use “index fossils” to define and identify geologic periods, which helps relatively date rocks ages.
By the other hand, absolute dating puts a specific number on the age of rocks (say 25 million years sold i.e.) with the use of more precise techniques. In this case, this method provides chronologically organized estimates of the age of geological materials related to fossils. Since elements such as calcium and potassium decay in their radioactivity, this phenomenon is used by geologists as a clock to determine the age at which rocks or fossils were formed. Knowing this, geologist design procedures called radiometric dating methods to date ancient events with the use of elements radioactivity decay.
