EES 1030 Lecture 8 Outline of Last Lecture I. Geological Time ScaleII. Geological History of OutcropsIII. Two ways to date geological eventsIV. Principle of UniformitarianismV. Principle of SuperpositionVI. Principle of Cross-Cutting RelationshipsVII. Principle of InclusionsVIII.UnconformitiesIX. Geological History of a regionX. Principle of Lateral ContinuityXI. Fossils and CorrelationXII. Fossils and DisconformitiesXIII.The geological time scaleOutline of Current Lecture XIV. Structure of an AtomXV. Atoms and IsotopesXVI.Radioactive DecayXVII. Requirements for Isotopic DatingXVIII. Carbon-14 or radiocarbon datingXIX.Radiometric Dating MethodsXX. Earth’s oldest rocksXXI.Sedimentary rocks: not easy!These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best Used as a supplement to your own notes, not as a substitute.XXII. Volcanic Ash LayersCurrent Lecture- Structure of an Atomo Nucleus contains most of the mass of the atom Protons with a positive charge- Atoms and Isotopeso Atomic number = number of protons. All atoms of a particular element have the same atomic numbero Mass number = number of protons + neutrons. Atoms of a particular element can have different numbers of neutrons  isotopes Example: Rubidium (37 protons): two naturally occurring isotopes- Radioactive Decayo Radioactivity: Spontaneous changes (decay) in the structure of certain unstable atomic nucleio Parent: an unstable radioactive isotope.o Alpha decay: loss of 2n + 2po Beta decay: n  p + electrono Electron capture: p + electron  n Which of the following is correct for isotopes of the same element? The atoms have different numbers of neutrons but the same number of protonso How is radioactive decay useful for dating?o The rate at which radioactive decay occurs for a particular- Requirements for Isotopic Datingo Decay rates constant & precisely known: no evidence of theoretical basis to expect decayrates to vary under the physical conditions within the Earth or over timeo Closed system: parent & daughter elements must not diffuse (leak) in or out of the mineral.o Diffusion stops below a certain temperature (150-800 Celsius) which varies for different elements and different mineralso Chemical weathering of sample a problemo Minerals in slowly-cooled metamorphic rocks can give us different ages by different techniqueso Radiometric dating is a complex procedure that requires precise measurements- Carbon-14 or radiocarbon datingo 14C: half-life is 5730 yearso Only for very young samples, < 40,000 yearso Formed continuously in upper atmosphere by high-energy cosmic rayso Incorporated into all living organismso Can date wood, charcoal, bone, shells- Radiometric Dating Methodso Uranium-Lead- Earth’s Oldest Rockso Acasta Gneisses: Yellowknife area of the NW Territories near Great Slave Lake in Canadao 4.03 Billion years old- Sedimentary Rocks: Not easy!o Detrital mineral grains will give age of original source rocko Cement minerals give younger ages than sediment deposition ageo Date indirectly from volcanic igneous rocks interbedded with sedimentary rock units: pyroclastic ashes, lava flows- Volcanic Ash layerso Blanket a wide geographical area. Distinctive time marker horizon. Often contain minerals that can be dated by radiometric