Test 2 Requirements - Introduction to Physical Geology...

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Introduction to Physical Geology Review sheet and concept summary, part II February 2008 VII. Geologic time (T&L chapter 9) a. Relative dating i. Key principles 1. Law of Superposition 2. Principle of Original Horizontality 3. Principle of Cross-Cutting Relationships Be able to apply these principles to interpret a sequence of events, for example in a block diagram or photograph. (T&L Figures 9.8, 9.18 and 9.19 provide good fodder for practice) ii. Unconformities and their meaning Recognize an unconformity in a diagram, and understand that it indicates an interval of erosion. b. Absolute dating i. Types of absolute dating 1. Layer counting methods: tree rings, varves, ice core layers, etc. 2. Radiometric methods (our focus) 3. Other methods ii. Radiometric dating 1. Examples of radioisotopes and their daughter products a. Rate of decay determined in laboratory 2. Definition of half life 3. Parent and daughter isotopes 4. Daughter-to-parent ratio (in a closed system) and how this changes over time 5. Radioactive decay is a statistical process – the time of decay of any particular atom can’t be predicted – but the rate of a decay of a large population of unstable atoms is constant for any given isotope Understand the assumptions you make when you apply a radiometric method such as U238 Pb206 • Be able to derive an age from a daughter-to-parent ratio (and vice versa) • Understand the relationship between fraction of parent isotope remaining and time elapsed VIII. Weathering and Soils (T&L chapter 6) a. Weathering i. Physical 1. Involves physical disruption of rock 2. Some common forms
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a. Frost wedging b. Fracturing due to erosional unloading c. Biological weathering (e.g., tree roots) d. Thermal expansion e. Salt 3. The presence and rate of these processes depends strongly on climate, and to some extent on material ii. Chemical 1. Chemical reactions with minerals in a rock 2. Common forms: a. Dissolution i. Natural acid (carbonic) in rain water ii. Acts on soluble minerals such as CaCO3 and evaporites b. Oxidation i. Combination of certain elements with oxygen; example of rust c. Hydrolysis i. Direct reaction with water ii. Turns feldspar into clay iii. Main controls on weathering rates 1. Climate 2. Parent material 3. Rates vary widely • Be familiar with the main types of physical and chemical weathering. • Understand that these processes turn rock into sediment.
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