EESA06 Final Exam Ch19 Summary + 40 MCQ/T or F

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Environmental Science
Nick Eyles

PHYSICAL GEOLOGY AND THE ENVIRONMENTND2 CANADIAN EDITIONChapter 19 Time and GeologyChapter SummaryThe principle of uniformitarianism a fundamental concept of geology states that the present is the key to the pastRelative time or the sequence in which geologic events occur in an area can be determined by applying the principles of original horizontality superposition lateral continuity and crosscutting relationshipsUnconformities are buried erosion surfaces that help geologists determine the relative sequence of events in the geologic past Beds above and below a disconformity are parallel generally indicating less intense activity in the Earths crust An angular unconformity implies that folding or tilting of rocks took place before or around the time of erosion A nonconformity implies deep erosion because metamorphic or plutonic rocks have been exposed and subsequently buried by younger rockRocks can be correlated by determining the physical continuity of rocks between the two areas generally this works only for a short distance A less useful means of correlation is similarity of rock types which must be used cautiouslyFossils are used for worldwide correlation of rocks Sedimentary rocks are assigned to the various subdivisions of the geologic time scale on the basis of fossils they contain which are arranged according to the principle of faunal successionNumerical agehow many years ago a geologic event took placeis generally obtained by using isotopic dating techniques Isotopic dating is accomplished by determining the ratio of the amount of a radioactive isotope currently in a rock or mineral being dated to the amount originally present The time it takes for a given amount of an isotope to decay to half that amount is the halflife for that isotope Numerical ages have been determined for the subdivisions of the geologic time scaleEESA06 Page 1 of 8
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