Chapter 5 Section 1 By: Mrs. Sergent
To Get You Thinking What does the following statement mean? "The present is the key to the past."
The Principle of Uniformitarianism Processes that we observe today, such as erosion and deposition, remain uniform , or do not chance, over time. Uniformitarianism is the idea that the same geologic processes that are shaping Earth today have been at work throughout Earth's history.
Figure 1 How would this diagram support uniformitarianism?
Catastrophism is the principle that states that all geologic change occurs suddenly . Supporters of catastrophism thought that Earth's features, such as mountians, canyons, and seas, formed during rare, sudden events called catastrophes . These unpredictable events caused rapid geologic change over large areas, sometimes even globally.
Modern Geology-A Happy Medium Today, scientists realize that neither uniformitarianism nor catastrophism accounts for all geologic change throughout Earth's history. Although most geologic change is gradual and uniform , catastrophes that cause geologic change occured during Earth's long history.
Scientists use two methods to determine the age of objects in sedimentary rocks. 1. Relative Dating 2. Absolute Dating Layers of sedimentary rock have different thicknesses based on the rate at which sediments are deposited . The bottom layers of rock are generally the oldest . The top layers of rock are generally the youngest .
Scientists can use the order of these rock layers to determine the relative age of objects within the layers. Estimating the age of rock layers in this way is called relative dating . The geologic column is an ideal sequence of rock layers that contains all of the known fossils and rock formations on Earth.
Figure 4 Which of the three layers contains the oldest rock layers? The youngest? How do you know?
Absolute Dating Absolute Dating is a method that measures the age of fossils or rocks in years. In absolute dating, scientists examine atoms . The time that it takes for half of the unstable atoms in a sample to decay is the half-life of that type of atom. By measuring the ratio of unstable atoms to stable atoms, scientists can determine the approximate age of a sample of rock.
Paleontology-The Study of Past Life Paleontology is the science involved with the study of past life . The data that paleontologist use are fossils . Fossils are the remains of organisms preserved by geologic processes.
Exit Questions 1. What is uniformitarianism? 2. What is catastrophism?
Homework Section Review P.133 1-2, 4, 7-8 & 11
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