With out individual time stamps the process of dating these structures could become extremely difficult.
To deal with many of these problems geologists utilize two types of geologic time: relative time and absolute time.
Thus, in a sequence of layers that have not been overturned by a later deformational event, the oldest layer will be on the bottom and the youngest layer on top.
This is the same principle used to determine relative age in the trash pits discussed previously.
A more modern way of stating the same principle is that the laws of nature (as outlined by the laws of chemistry and physics) have operated in the same way since the beginning of time, and thus if we understand the physical and chemical principles by which nature operates, we can assume that nature operated the same way in the past.
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.
Relative time places events or formations in order based on their position within the rock record relative to one another using six principles of relative dating.
Relative time can not determine the actual year a material was deposited or how long deposition lasted; it simply tell us which events came first.
Principles of Stratigraphy Stratigraphy is the study of strata (sedimentary layers) in the Earth's crust.
Geologist in the 1800s worked out 7 basic principles of stratigraphy that allowed them, and now us, to work out the relative ages of rocks.