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From the beginning of this course, we have stated that the Earth is about 4.6 billion years old.
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.
where the same features that could be seen forming in modern environments.
He concluded that process that are currently operating on the Earth must be the same processes that operated in the past.
The goal of this lecture is come to come to a scientific understanding of geologic time and the age of the Earth.
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).
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.
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.