Earth Science 11ed Edward J Tarbuck Frederick K Lutgens Geologic Time Chapter 11 Leaves of History American Geologic Exploration John Wesley Powell Colorado River Expedition 1869 Grand Canyon is Earth s Book of Revelations Historical notes Catastrophism Landscape developed by catastrophes James Ussher mid 1600s concluded Earth was only a few thousand years old Historical notes Modern geology James Hutton Theory of the Earth Published in the late 1700s we find no vestige of a beginning no prospect of an end Modern geology Uniformitarianism Fundamental principle of geology The present is the key to the past 1 Modern geology Relative dating Most of geology represents uniformitarianism However catastrophism has its place in our understanding Tsunamis Krakatau Meteor impacts Placing rocks and events in proper sequence of formation Deciphering Earth s history from clues in the rocks Principles of Relative Dating Principle of original horizontality Principle of lateral continuity Principle of superposition Principle of cross cutting relationships Principle of inclusion Nicolaus Steno 1636 1686 1669 work relates to deposition of sediment Principle of original horizontality Principle of lateral continuity Principle of superposition http www ucmp berkeley edu history steno html Principle of Original Horizontality Lateral Continuity Sediment is deposited horizontally http faculty icc edu easc111lab labs labf orig horizontality jpg http cse cosm sc edu hses RelatDat pages lateral htm 2 Principle of Superposition Nicklaus Steno 1669 Oldest rocks are on the bottom Stratigraphic Superposition Oldest rock A Younger rocks above E is the youngest http cse cosm sc edu hses RelatDat pages superpos htm Superposition is well illustrated by the strata in the Grand Canyon James Hutton 1726 1797 1785 lectures Concerning the system of the Earth its duration and stability to the Royal Society of Edinburgh Principle of crosscutting relationships Principle of inclusions http www history mcs st andrews ac uk Mathematicians Hutton James html Principle of Cross cutting Relationships Cross cutting relationships Younger feature cuts through an older feature Something must exist first to be cut by another thing The things cutting may be things such as igneous intrusions Or they may be events like fault breaks folding or erosion periods 3 Folding occurred after deposition Inclusions One rock contained within another Rock containing the inclusions is younger than the one the inclusions are derived from http rst gsfc nasa gov Sect2 Sect2 6 html How inclusions form The fragments are included with the deposition of rock on top of the weathered surface Formation of Inclusions Two different modes of inclusion http www rohan sdsu edu rhmiller geologictime GeologicTime htm Inclusions of granite in sedimentary deposit formed later than granite Inclusions of sediment in granite granite formed later than sediment 4 Unconformities A break in the rock record Three types of unconformities Angular unconformity Disconformity strata on either side are parallel Nonconformity Formation of an angular unconformity Angular Unconformity Tilted rocks are overlain by flat lying rocks Remember the principle of original horizontality Simple angular unconformity http www grisda org colorado index htm Folding erosion deposition folding Nonconformity Metamorphic or igneous rocks below Younger sedimentary rocks above http rst gsfc nasa gov Sect2 Sect2 6 html 5 Disconformity Nonconformity Gap in sedimentation that may have erosion also Represents an interval in geologic time without rock deposited Most difficult of the three unconformities to detect Strata on either side are parallel Several unconformities are present in the Grand Canyon Principles of Relative Dating Superposition Original Horizontality and Lateral Continuity Inclusions Crosscutting Relationships Unconformities Relative Dating Exercise http www winona edu geology MRW maps htm 6
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