Determining Absolute Age Chapter 8 - 2 Determining Absolute Age

Absolute Age Numeric age Observed geologic processes Chemical composition of rocks

Rate of Erosion Measure rate at which streams erode a bed Can estimate the age of the rock

Niagara Falls Erodes at 1.3 m per year. 9,900 years

Rate of Deposition How long it takes for sediment to be deposited Floods can deposit faster

Varve Count Rings on a tree Varve - Sedimentary deposits in annual layers

Glacier lakes – Summer melt deposits in layers Coarse – bottom Fine - top

The Atom

Radiometric Dating Radioactive isotope – nuclei emit particles Compare % of radioactive to stable isotopes

Half-Life Time it takes for ½ the mass of an element to decay Parent to daughter

Radioactive Isotope Table 1 page 195 Different elements take different amounts of time to decay

Carbon Dating Younger rocks How much organic material is in the rock

Carbon-14 combines with oxygen to form CO2 Most CO2 has carbon-12 Pants and animals take in CO2 Die and become part of the rock

Organic material in rock – compare C-14 to C-12 Constant while alive Ration changes when dead