# Introduction to Absolute (Radiometric) Dating. Learning Targets 4a) I can distinguish between absolute and relative dating. (DOK 1) 4b) I can define what.

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Learning Targets 4a) I can distinguish between absolute and relative dating. (DOK 1) 4b) I can define what an isotope is and describe how radioactive isotopes decay (DOK 1) 4e) I can identify and analyze key strengths and limitations of using radioactive decay in absolute dating. (DOK 1-2) Essential Question How do scientists use absolute dating to build a model of the Earth’s history?

Absolute Dating

Isotopes Two or more of the same element with different masses. Have the same number of protons but number of neutrons changes. http://education.jlab.org/glossary/isotope.gif

Radioactivity o Some atoms are not stable o These atoms emit particles to achieve stability http://abyss.uoregon.edu/~js/images/radioactivity.gif

Radioactivity There are three types of particles emitted: 1.Alpha particles 2.Beta Particles 3.Gamma Rays

Alpha Particles o Charge = +2 (2 protons) o Mass = 4 (2 protons + 2 neutrons) o Large, easily stopped by paper © The Geological Society of America, 2003

Beta Particles o Charge = -1 o Mass = negligible o Small, more penetrating particle, but still easily stopped http://sol.sci.uop.edu/~jfalward/elementaryparticles/betaparticleenergy.JPG

Beta Particles o Neutron decays into a proton and an electron o Electron leaves o Atomic number goes up 1 http://sol.sci.uop.edu/~jfalward/elementaryparticles/betaparticleenergy.JPG

Gamma Rays o Pure energy o No change in atom o Very penetrating, cause damage http://www.arpansa.gov.au/images/basics/all_pen.jpg

Absolute (Radiometric) Dating o Based on decay rates of different atoms o Rate of decay stated as half-life http://www.bible.ca/tracks/dating-radiometric-cartoon.gif

Half-Life Time it takes for ½ of the radioactive atoms to decay into its daughter atoms © The Geological Society of America, 2003

Half-Life Atoms used in geologic dating have long half- lives ParentDaughterHalf-Life Uranium-238Lead-2064,470 million years Uranium-235Lead-207704 million years Potassium-40Argon-401,250 million years Rubidium-87Strontium-8748,800 m. y. Carbon-14Nitrogen-145,730 years

Half-Life Scientists use both decay and production curves © The Geological Society of America, 2003

Assigning Ages Using the proportion of daughter atom in a sample, its age can be determined http://upload.wikimedia.org/wikiversity/en/thumb/4/4b/Radiometricdatingmineral.png/400px-Radiometricdatingmineral.png

Major Principle of Absolute Dating

Check for Understanding Explain the main concepts of how scientists use absolute (radiometric) dating to determine the age of objects

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