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Relative dating and Absolute dating

Page history last edited by PBworks 12 years, 9 months ago

 Relative time                                    Absolute Time


-Places events in order                                                  -Gives a specific date

-do not tell actual age.                                                  -uses radioactive decay of certain elements to give age of rock/fossil





Relative Dating

Law of superposition

           - the oldest rocks are at the bottom

           -the youngest rocks are on top.


Law of Crosscutting relationships

           -An igneous intrusion is younger than the rock it intruded throught


Law of Included Fragments

           -Rocks found inside other rocks must be older


Absolute Dating


           Uranium- Lead method


                                -Uranium decays into lead

                                -half life of 4.5 billion years

                                -ratio of uranium to lead changes through time. Comparing the current ratio with the original ratio helps to determine how long the uranium has been decaying.


                 Potassium- Argon Method


                                -Potassium 40 decays into argon 40

                                -half life 1.3billion years

                                -ratio of  40    to 40    changes   

                                                  K          R

                 Carbon 14 method

                               -Carbon 14 decays to nitrogen 14

                               -used for organic matters

                               -half life of 5730 years

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