By carefully digging, we have found that each trash pit shows a sequence of layers.Although the types of trash in each pit is quite variable, each layer has a distinctive kind of trash that distinguishes it from other layers in the pits.Geologists generally know the age of a rock by determining the age of the group of rocks, or formation, that it is found in.
This then can be used to deduce the sequence of events and processes that took place or the history of that brief period of time as recorded in the .
is a way to use geometric relationships between rock bodies to determine the sequence of geologic events in an area.
Relative dating is different from absolute dating in which specific dates are assigned to geologic events (we will discuss absolute dating techniques later).
Radiometric dating and certain other approaches are used to provide absolute chronologies in terms of years before the present.
The two approaches are often complementary, as when a sequence of occurrences in one context can be correlated with an absolute chronlogy elsewhere.