112-pp8 - UNIVERSITY OF SOUTH ALABAMA Last Time GY 112:...

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1 GY 112: Earth History Lecture 8: Radiometric Dating UNIVERSITY OF SOUTH ALABAMA Last Time 1. Relative vs. Absolute Dating Techniques 2. Magnetostratigraphy 3. Fission Track Dating (Web Lecture 7) Geological Dating Techniques Relative Techniques: Assigns an age to a rock that puts it into a narrow range (e.g., mid-Devonian; Late Cretaceous, upper Pliocene). Absolute Techniques : Assigns an age to a rock that is a number (e.g., 354.7 +/- 21.3 MA; 1,453 KA +/- 67 KA). Magnetostratigraphy • Chron – Polarity time-rock unit – Period of normal or reversed polarity • Normal interval – Same as today –B l a ck • Reversed interval – Opposite to today – White Magneto- stratigraphy Absolute Techniques • Fission-Track Dating – Measure decay of uranium 238 by counting number of tracks
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2 Today’s Agenda 1. Isotopes and Radioactive Decay 2. Radiometric Dating 3. Mass spectrophotometers (Web Lecture 8) Radioactive Elements Uranium (and others) are unstable Atoms & Atomic Particles • Atoms are composed of 3 fundamental particles: 1) Protons 2) Neutrons 3)Electrons • Protons & Neutrons always reside in the center of the atom termed the nucleus • Electrons are always located in the electron cloud in complex orbitals where they “orbit” the nucleus Nucleus (Protons + Neutrons) Electron Cloud (Electrons) Atomic Number & Weight • By convention, we put both numbers on a letter that symbolizes that particular element: 1 H 12 He 46 C 12 Atomic Number & Weight • By convention, we put both numbers on a letter that symbolizes that particular element: 1 H He C 12 Atomic Number Atomic Weight Isotopes • The number of protons and electrons for an element does not vary, but the number of neutrons can. e.g., hydrogen
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3 Isotopes • The number of protons and electrons for an element does not vary, but the number of neutrons can. e.g., hydrogen + - 1 H 1 - Proton Neutron Electron Isotopes • The number of protons and electrons for an element does not vary, but the number of neutrons can. e.g., hydrogen + - 1 H 1 - 1 H 2 - Proton Neutron Electron Isotopes • The number of protons and electrons for an element does not vary, but the number of neutrons can. e.g., hydrogen + - 1 H 1 - 1 H 2 - 1 H 3 - Proton Neutron Electron Isotopes • The number of protons and electrons for an element does not vary, but the number of neutrons can.
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This note was uploaded on 02/04/2012 for the course GLY 112 taught by Professor Haywick during the Spring '12 term at S. Alabama.

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112-pp8 - UNIVERSITY OF SOUTH ALABAMA Last Time GY 112:...

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