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Aging Earth’s Layers Lecture Today Stress on Earth’s Crust Tension, compression and shearing cause crustal deformation Faults Shearing Causes transform or lateral faults Compression Causes reverse faults Tension Causes normal faults May form fault bock mountains Sharp angular and steep on one side Gradual slope on other Plateaus Flat topped May also be formed by lava flows Formed by expansion of inner earth as increases in temperature Stress on Earth’s Crust: Folding Caused by compression Top of fold is anticline Bottom is syncline May cause folded mountains Folding may be beneath surface Fold or Fault Stress may do either Depends on Temperature Pressure Type of rock Time and duration of stress Stress on Earth’s Crust: Intrusions Magma may push on layers of rock above it Creates dome mountains Black Hill in South Dakota Absolute Dating Radio Carbon dating Uses radioactive elements Change at predictable rates Gives accurate age Relative Dating Uses comparison of ages Looks at ages and events rock layers represent Can only find sequence of events Does not give actual age Principle of Uniform Processes : Uniformitarianism Opposes catastrophism Processes changing Earth today changed Earth in past Principle of Superposition Bottom layers in geologic column are oldest Relative Dating Changes in order may be caused by Folding Faulting Magma intrusions Erosion- UNCOMFORMITY Folds and Faults May change order of rock layers in geologic column Oldest to youngest order no longer applies Relative Dating Geologic History Numbers rock layers from oldest to youngest Includes a written paragraph explaining when folding, faulting, erosion and magma intrusions occurred