Boundary stratotypes

Boundary stratotypes are specific, well-defined locations around the world that scientists use as reference points to mark the boundaries between different geological time periods or units. Think of them as official “timestamp” sites in Earth's history. These sites contain characteristic rocks or fossils that clearly represent a particular time boundary, helping geologists identify and correlate the ages of rocks elsewhere. They ensure consistency and accuracy in understanding Earth’s geological timeline by providing a standard point of comparison for defining changes in Earth's history.