2 Absolute Age/Dating the numeric age of an object or event Stated in yearsVariety of methods can be used
3 Methods of Absolute Age Dating Rates of ErosionRates of DepositionVarve CountRadiometric DatingCarbon Dating
4 Method 1: Rates of Erosion Uses the rates at which geological features erodeOnly 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 CountVarve-banded layer of sand & silt that is deposited annually in a lakeOne varve represents one year of depositionBy counting the varves scientists can estimate the age of sediment
8 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.
9 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.