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Time and Geology. The Present is the Key to the Past –Catastrophism-October 23, 4004 9:00AM James Ussher, Bishop of Ireland –Uniformitarianism- James.

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Presentation on theme: "Time and Geology. The Present is the Key to the Past –Catastrophism-October 23, 4004 9:00AM James Ussher, Bishop of Ireland –Uniformitarianism- James."— Presentation transcript:

1 Time and Geology

2 The Present is the Key to the Past –Catastrophism-October 23, :00AM James Ussher, Bishop of Ireland –Uniformitarianism- James Hutton (1795) uniform rate of geologic processes –Actualism gradualism and catastrophism shape geologic processes Relative Time –Sequence of Geologic Events Absolute Age

3 Principles Used to Determine Relative Age Superposition- Nicolas Steno –Progressively younger from bottom => top Lateral Continuity Original Horizontality- Steno Contacts Formations Cross-cutting Relationships- Lyell –Truncated units (dikes and faults)

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6 Correlation Physical Continuity of Lithologic Units Similarity of Rock Types Superposition Correlation by Fossils –Principle of Faunal Succession –Index Fossil –Fossil Assemblage

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8 Correlation Correlation by Fossils –Principle of Faunal Succession Wm. Smith & Georges Cuvier Organism succeed one another in lithologic strata One organism will NOT be found in rocks of widely different ages –Index Fossil Wide geographic distribution Of limited life span as a species Easily identifiable –Fossil Assemblage

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10 Standard Geologic Time Scale Established in the 19th century- Sedgwick & Murchinson Based on Fossil Assemblages Eons, Eras, Periods, and Epochs –PHANEROZOIC since 544 m.y.b.p. Paleozoic Era m.y.b.p. Mesozoic Era m.y.b.p. Cenozoic Era 65 m.y.b.p.-present –Tertiary & Quaternary Periods »Recent (Holocene) Epoch last 10,000 years Precambrian- All time before Paleozoic

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12 Unconformities Unconformity - surface that represents a gap in the geologic record –Disconformity - contact representing missing parallel beds of sedimentary beds –Angular unconformity - younger strata overlie an erosion surface on tilted or folded layers –Nonconformity - erosion surface on plutonic or metamorphic rock

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14 Unconformities Unconformity - surface that represents a gap in the geologic record –Disconformity - contact representing missing parallel beds of sedimentary beds –Angular unconformity - younger strata overlie an erosion surface on tilted or folded layers –Nonconformity - erosion surface on plutonic or metamorphic rock

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16 Unconformities Unconformity - surface that represents a gap in the geologic record –Disconformity - contact representing missing parallel beds of sedimentary beds –Angular unconformity - younger strata overlie an erosion surface on tilted or folded layers –Nonconformity - erosion surface on plutonic or metamorphic rock

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18 Unconformities Unconformity - surface that represents a gap in the geologic record –Disconformity - contact representing missing parallel beds of sedimentary beds –Angular unconformity - younger strata overlie an erosion surface on tilted or folded layers –Nonconformity - erosion surface on plutonic or metamorphic rock

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21 Absolute Age Isotopic Dating Isotopes and Radioactive Decay –Isotopes - Differing number of neutrons, but same number of protons –Radioactive Decay - Spontaneous nuclear disintegration of unstable isotopes Daughter Product Half-life –Various techniques (e.g. U-Pb, K-Ar, radiocarbon dating)

22 Absolute Age Uses of Isotopic Dating –Igneous Rocks Reliability of Isotopic Dating –Accuracy and precision of analytical instrumentation

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25 Isotopic Decay Unstable Nucleus –spontaneously change into another type of atom Decay through Beta emission (Rb>Sr), Positron emission(N>C), Electron capture (K>Ar), Alpha emission (U>Th), Spontaneous fission Decay Rate is Constant, it depends on the particular isotope

26 Radioactive Decay Series

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28 Age of the Earth Early speculation Dating of meteorites and moon rocks Between 4.5 & 4.6 billion years old Comprehending Geologic Time

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