Relative Age 1 Relative age dating a Qualitative b Relative ages 2 Techniques a Steno s principles b c Intrusion Inclusion 3 Requires strata to be in contact no one location has all rocks deposited 4 Techniques continued a Smith fossil succession b Cuvier i Being able to date strata with fossils that are included i Species become extinct biota replaced by others 1 Sea level rises or falls Absolute Age 1 Absolute age dating a Quantitative b Numerical value for an age i Isotopic radiometric dating Geologic Time Scale 2 Development a Fossil record is key element i Relative first and last occurrences in strata b Geologic systems of rock contain specific fossils i Can t objectively confuse Cambrian rocks for Ordovician rocks because the fossils are different c Geologic systems defined based on their distinctive type of sedimentary rock Correlation 3 Stratigraphy study of stratified rock a Geometric arrangement of sediment beds b Composition c Mode of origin d Age 4 Geologic time scale divided into time units 5 Rock record divided into rock units a Chronostratigraphic units during a particular time interval 6 Stratigraphic correlation areas i Lithocorrelation i All rocks of a time rock unit represent all strata in the world deposited a Establish the relative equivalence of rock unit in geographically separated ii Bio correlation b Bio stratigraphic correlation units bio zone i Body of rock whose lower layer and upper layer are based on the range of one or more taxa in the stratigraphic record 7 Index or guide fossil concept a 5 criteria i abundant enough in the record to find easily ii easily distinguished iii geographically widespread iv occurs in many different sedimentary rocks v narrow stratigraphic range allowing for precise correlation 8 top and base of lithologic unit doesn t have to have same age everywhere a grand canyon i 3 thick marine formations are exposed b in 1940s Mckee explained that the 3 formations couldn t have been everywhere laid done in layer cake fashion 1 after the other i landward shift in environment Environmental Facies 1 lithology and biota are important 2 body of rock with a set of physical and biological characteristics representing a particular formation 3 Grand Canyon 3 formations represents 3 different marine environment grading into one another but existing at the same time 4 Establish the relative equivalence of rock units in geologically separated areas Correlation 1 Magnetic stratigraphy 2 Seismic stratigraphy 3 Event stratigraphy a Marker bed b Sequence a Lithocorrelation b Biocorrelation c Seismic d Magnetic e Event Absolute Age 1 How old is the Earth a 4 6 billion years old 2 How is it determined a Radioactive decay with isotopes in igneous rock b Early estimates based on i Saltiness of ocean equilibrium ii Accumulated sediment neglected sediment iii Temperature rates of change misunderstood 3 Radioactive decay a Decay of atoms of one element into another b Such atoms are radioactive isotopes i Radioactive unstable decay spontaneously ii Parent iii Daughter c Occurs at a constant rate i How long it takes of parent to decay to daughter ii Ratios within a particular mineral can be used to measure the amount of time that has passed since mineral formed 1 Isotopic dating 2 Minerals formed from cooling magma works well 4 Isotopic dating a After certain amount of time i parent daughter b ratio of parent to daughter gives the age Isotopic Correlation 1 Correlation of strata a Using global shifts in the ratios of stable isotopes i Ratios can be preserved in the skeletons of marine organisms 2 Relative ages lots of information in sediment rocks a Correlation b Stratigraphic principles c Fossils 3 Absolute a Datable minerals b Restriction on strata