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29.3 A BSOLUTE T IME

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H ISTORICAL M ETHODS Counting rigs in trees – more accurate, but cannot calculate very old material.

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H ISTORICAL M ETHODS Estimating rates of erosion and sedimentation – Only useful for younger geologic features.

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H ISTORICAL M ETHODS Counting Varves – The sediments that form in bodies of water annually. (Optional) Ex. The glacial lakes deposit a like thin layer in the summer and a dark layer in the winter.

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R ADIOACTIVITY Radioactive Decay – the process of an atomic nucleus losses E by emitting ionizing particles and radiation. (Alpha, Beta & e- capture)

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R ADIOACTIVITY Radioactive Decay Alpha Decay : An alpha particle (2 e+ and 2 e-) are emitted.

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R ADIOACTIVITY Radioactive Decay Beta Decay: A neutron disintegrates into a e+ and a e- (beta particle)

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R ADIOACTIVITY Radioactive Decay e- capture: A e+ captures an e- and becomes a neutron.

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R ADIOACTIVITY Radioactive Decay As decay continues the atom becomes an isotope of a different element. Continues until it becomes a stable (non radioactive isotope).

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R ADIOACTIVITY Radioactive Decay Parent Isotope – Original element/atom Daughter Isotope – product of the original. Ex. C14->N14

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H ALF L IFE The time it takes half an atoms radioactive material to decay to a stable product. U 238 has a half life of 4.5 b.y.

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R ADIOMETRIC D ATING Radiometric Dating The process of measuring the amount of parent and daughter material and using the ratio to find the age of the material. (Rocks, minerals and organic material)

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R ADIOMETRIC D ATING Radiocarbon Dating Using C12 and C14 to date dead organisms. (not useful for organisms older than 70,000 y.o.)

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R ADIOMETRIC D ATING Radiometric Dating U-Pb Dating: Used to date rocks that contain U and Pb. Not acurate for rocks less than 10 myo.

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R ADIOMETRIC D ATING Radiometric Dating Rubidium/Strontiu m dating, Used to date rocks that contain Rb and Sr. Used for extremely old rocks.

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R ADIOMETRIC D ATING Radiometric Dating Potassium/Argon dating, Used to date rocks that contain K and Ar. Can be used to date rocks as young as 50000 y.o. Met/Sed/Ig Rocks

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