Learn how inclusions and unconformities can tell us stories about the geologic past.We'll even visit the Grand Canyon to solve the mystery of the Great Unconformity!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).
From the beginning of this course, we have stated that the Earth is about 4.6 billion years old.The method of reading the order is called stratigraphy (layers of rock are called strata).Relative dating does not provide actual numerical dates for the rocks.An isotope system is assumed to be a closed system with regard to the parent and daughter - they remain within the system and do not leave it, and at the same time no isotopes of the parent or daughter type enter the system from outside.(In reality, rocks, minerals and other geologic materials can be checked to see if the isotope system remained closed, rather than assuming so.) At time zero, 100% of the isotopes are the parent isotopes.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.Many of these organisms have left their remains as fossils in sedimentary rocks.Geologists have studied the order in which fossils appeared and disappeared through time and rocks. Fossils can help to match rocks of the same age, even when you find those rocks a long way apart.By the definition of a half-life, the amount of parent isotope at each half-life is half of what it was before the half-life elapsed.As the amount of parent isotope decreases by radioactive decay, the amount of the daughter isotope increases commensurately.