Definition of relative age dating
Once these age relations were worked out, another principle fell into place - the principle of fossil succession.We discuss the 7 principles of stratigraphy first and then see how these apply to fossils.
In order to do so we will have to understand the following: To better understand these concepts, let's look at an archeological example: Imagine we are a group of archeologists studying two different trash pits recently discovered on the Tulane University campus and at the Audubon Zoo (where they all aksed for you).Long before geologists tried to quantify the age of the Earth they developed techniques to determine which geologic events preceded another, what are termed "relative age” relationships.These techniques were first articulated by Nicolas Steno, a Dane living in the Medici court of Italy in the 17th C.Look at the many photographs of the Grand Canyon in your textbook.Note that you can follow the layers all along the walls of the canyon, and you can find the same layers on both sides of the canyon.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.
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.
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.
Principle of Uniformitarianism The principle of Uniformitarianism was postulated by James Hutton (1726-1797) who examined rocks in Scotland and noted that features like mudcracks, ripple marks, graded bedding, etc.