Relative Dating
Uploaded by Admin on Jan 22, 1999
The Fundamental Principles of Relative Dating
Relative dating involves placing events in their proper chronological sequence, that is, in the order of their occurrence (Dutch 1998). This type of dating tells us which geologic event happened first, but does not give an exact date to which something happened. There are several different methods that are used in relative dating. These are the fundamental methods that are used in the field by geologists' and earth scientists to gather information about the relative age of rock bodies and other cool geologic stuff. These principles are the principle of superposition, the principle of original horizontality, the principle of cross-cutting relationships, and the principle of inclusions.
The principle of superposition is defined as in the environment of an undisturbed layer of sedimentary rocks; the layers on the bottom are older than the layers towards the top. The pictures I have taken show very good examples of this. By using the principle of superposition we can know that the layers toward the bottom are older than the layers toward the top. The rock body shown in the pictures attached, started out as one layer, as millions and millions of years passed more layers of sedimentary rock were placed on top of each other one after another, each layer was deposited at a later time than the one before it. The youngest layer is on the top, and the oldest layer is on the bottom.
This principle was founded by the Danish anatomist Nicolas Steno, who noted that during floods, streams spread across their floodplains and deposit layers of sediment that bury organisms dwelling there. He noticed that later floods produce younger layers of sediments that are deposited or superposed over previous deposits (Dutch 1998). This is just one example how superposition can occur on a smaller scale. The principle of superposition can also help give a relative date of any type of biological remnants that are contained in the layers.
The next principle that I am going to discuss is the principle of original horizontality. This principle states that rocks are originally layered in horizontal planes, and any inclining area is caused by tilting of the rocks. Steno came up with this principle also (Dutch 1998). In picture number one it is fairly noticeable that the rock layers are higher on the left side than on the right. This tells us that during some period of time, the...