Absolute Age Determining How Old Geologic Features Are

Absolute Age Absolute Age is the numeric age of an object or event, often stated in years before the present.

Ways to Determine Absolute Age Rates of Erosion Rates of Deposition Varve Count Radiometric Dating

Rates of Erosion By measuring how fast a river erodes, geologists can estimate how old it must be. Only accurate for 10,000 – 20,000 years old. Niagara Falls erodes at the rate of 1.3 meters per year

Erosion of Niagara Falls

Rates of Deposition Geologists estimate that it takes about 1,000 years to deposit 30 centimeters of sedimentary rock. This is not a highly accurate way of measuring age but can give useful estimates.

Varve Count Varves are sedimentary rock layers that occur annually. Caused by glaciers freezing and thawing. Just like tree rings! (Dendrochronology)

Radiometric Dating A method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope.

Most rocks contain small amounts of radioactive isotopes (parent isotopes). Radioactive isotopes emit particles and energy at a very constant rate. As the radioactive isotopes emit particles they change into new elements (daughter isotopes)

Half-Life The time required for one half of a sample of radioactive isotope to decay to daughter isotopes. Start half-lifehalf-lifehalf-lifehalf-life

Different radioactive isotopes have different half-lives. Long half-lives are useful for measuring older objects, while short half-lives are better used for younger objects.

Carbon-14 Dating Carbon-14 dating (radiocarbon dating) is used to measure the age of organic (once living) objects less than 70,000 years old. Rocks can be measured with this method if organic material is trapped in the rock and the organic material is dated.