Geologic time rock dating
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).Distinguishing nonconformity and intrusive contact Nonconformity: The sedimentary rock was deposited on the erosion surface of the older rock unit, thus the sedimentary rock is younger. Dikes may cut through the igneous body but stop at the nonconformity.Intrusive contact: intrusion is younger than the surrounding sedimentary rocks. A zone of contact metamorphism may form surrounding the igneous body.
Absolute dating was made possible only after the discovery of radioactivity.
The KT extinction At the boundary between Cretaceous (the last period of Mesozoic) and Tertiary (the first period Of Cenozoic) about 66 million years ago, known as KT boundary, more than half of all plant and animal species died in a mass extinction.
The boundary marks the end of the era in which dinosaurs and other reptiles dominated and the beginning of the era when mammals became important.
An angular unconformity indicates a long period of rock deformation and erosion.
Disconformity A disconformity is a minor irregular surface separating parallel strata on opposite sides of the surface.
Prior to the late 17th century, geologic time was thought to be the same as historical time.