What is stratigraphy dating
Each layer is compressed by the weight of those above it and becomes sedimentary rock. That is, wherever the layers of rock are exposed -- in a road cut, a steep river valley, a cliff face -- we can be fairly certain that the sediments get older as we go down the rock column and younger as we go up.
Radioactivity was not discovered until a century later (by Roentgen).Thus, the early geologists had no method to determine the absolute dates of the rocks they studied.However, they soon developed quite sophisticated techniques for relative dating.These techniques were developed using sedimentary successions.Mountains are raised by processes deep within the earth which push up molten igneous rock.Sooner or later, this material is worn down by wind, water, and chemical or biological erosion.
The rock is eroded into sediment -- sand or dust or gravel -- and settles over a broad area.
Most of the earth is covered in layers of sediment, as new sediment settles on top of old sediment.
Why do we bother with all these weird names for different time slices?
Actually, almost all of the time periods in the Precambrian are based on radiometric dates. As soon as stratigraphers can find enough information, they will change the simple date ranges to more complex entities defined in some other way.
Are they just trying to make things more complicated?
Actually there are three primary reasons for using this system. The science of stratigraphy was born at the same time as geology, early in the Nineteenth Century.