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Absolute Age Dating

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  1. Absolute Age Dating

  2. Absolute Age/Dating • the numeric age of an object or event • Stated in years • Variety of methods can be used

  3. Methods of Absolute Age Dating • Rates of Erosion • Rates of Deposition • Varve Count • Radiometric Dating • Carbon Dating

  4. Method 1: Rates of Erosion • Uses the rates at which geological features erode • Only practical for geological features that formed within the past 10,000-20,000 years. • Example: scientists can measure the rate at which a stream erodes in its bed to estimate the age of the stream.

  5. Method 2: Rates of Deposition • Scientists use the rate at which sediment is deposited for common sedimentary rocks such as limestone, shale, and sandstone. • Generally, about 30cm of sedimentary rock are deposited over a period of 1,000 years. • Not always accurate—floods and erosion can affect the average rate.

  6. Method 3: Varve Count • Varve-banded layer of sand & silt that is deposited annually in a lake • One varve represents one year of deposition • By counting the varves scientists can estimate the age of sediment

  7. Method 4: Radiometric dating • Method of comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope. • Radioactive isotopes have nuclei that emit particles & energy at a constant rate regardless of surrounding conditions.

  8. Method 5: Carbon Dating • C14 dating/radiocarbon dating • Used to date younger rock layers by dating organic material found within the rock. • The ages of wood, bones, shells & other organic remains that are included in the layers & are less than 70,000 years old can be determined.

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