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Earth History

Earth History. Rocks record geological events and changing life forms of the past. Uniformitarianism. Principle of Uniformitarianism “The present is the key to the past.” Geologic forces at work today also occurred in the past. Only the rate, intensity and scale have changed.

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Earth History

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  1. Earth History • Rocks record geological events and changing life forms of the past.

  2. Uniformitarianism • Principle of Uniformitarianism“The present is the key to the past.” • Geologic forces at work today also occurred in the past. Only the rate, intensity and scale have changed.

  3. Relative dating • Sequence in which events occurred, not how long ago they occurred. • The law of superposition: rocks on the bottom are older than the ones on top

  4. Ordering the Grand Canyon’s History

  5. Principle of Original Horizontality • The principle of original horizontality means that layers of sediment are deposited in a horizontal position.

  6. The principle of cross-cutting relationships states that the fault or intrusion is younger than the rocks affected. Principle of Cross-Cutting Relationships

  7. The Principle of Cross-Cutting A magma intrusion or a fault is younger than the rock it cuts across. Fault

  8. Fault

  9. Inclusions • Inclusions are rocks contained within other rocks. • Rocks containing inclusions are younger than the inclusions they contain.

  10. Unconformities • An unconformity represents a long period during which deposition stopped, erosion removed previously formed rocks, and then deposition resumed. 1. An angular unconformity indicates a period of deformation (folding or tilting) and erosion occurred.

  11. How did this happen?!!

  12. Formation of an Angular Conformity

  13. Unconformities 2. A nonconformityis when the erosional surface separates older metamorphic or intrusive igneous rocks from younger sedimentary rocks 3. A disconformity is when two sedimentary rock layers are separated by an erosional surface.

  14. A Record of Uplift, Erosion, and Deposition

  15. Correlation of Rock Layers • Correlation is establishing the equivalence of rocks of similar age in different areas.

  16. Correlation of Strata at Three Locations

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