Final Review Notes PT 2.doc

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Environmental Science
Nick Eyles

Chapter 19 Time and geology What is Uniformitarianism Uniformitarianismprinciple that geologic processes operating at the present are the same processes that operated in the past The present is the key to the past uniform rateActualismphysical laws are independent of time and location same meaning as uniformitar Geological Time Scalea sort of calander to which events and rock units can be referredEarth was only 6000 years oldbiblical chronology Noahs floodfeatures we observed in rocks and landscapes where supernaturally and catastrophicallyJames Huttonfather of modern day geology Charles LyellPrinciples of Geology book ogeological features could be explained by presentday processes How can the Sequence of Past Geological events be determined Numerical Age absolute ageage given in years or some other unit of time Relative Timethe sequence in which events took place not measured in time units ex Grand Canyon can be analyzed in 4 partsohorizontal layers of rockoinclined layersorock underlying the inclined layers plutonicmetamorphic rock othe canyon itself carved into these rocks Principles Used to Determine Relative Age Contactsboundary surface between two different rock types or ages of rocks Formationsbodies of rock of considerable thickness with recognizable characteristics that make each distinguishable from adjacent rock units named after local towns or landmarksStratigraphysubdiscipline of geology that uses interrelationships between layered rock or sediment to interpret the history of an area or region uses 4 principles 1Original Horizontalitythe disposition of most waterlaid sediment in horizontal or near horizontal layers that are essentially parallel to the Earths surface 2Superpositiona principle or law stating that within a sequence of undisturbed sedimentary rocks the oldest layers are on the bottom and the youngest on the top 3Lateral Continuityprinciple that states that an original sedimentary layer extends laterally until it tapers or things at its edges 4CrossCutting Relationshipsa principle or law stating that a disrupted pattern is older than the cause of disruption Other Time RelationshipsInclusionfragments included in a host rock are older than the host rock Unconformitiesa surface that represents a break in the geological record with the rock unit immediately above it being considerable younger than the rock beneath it 1Disconformitya surface that represents missing rock strata but beds above and below that surface are parallel to one another 2Angular Unconformityan unconformity in which younger strata overlie an erosion surface on tilted or folded layered rock implies the following sequence of events from oldest to youngestoDeposition and lithification of sedimentary rockoUplift accompanied by folding or tilting of layers oErosionoRenewed deposition on top of eroded surface3Nonconformityan unconformity in which an erosion surface on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rock oCrystallization of igneous or metamorphic rock at depth oErosion of a least several kilometers of overlying rock the great amount of erosion further implies considerable uplift of this portion of Earths crustoDeposition of new sediment thick eventually becomes sedimentary rock on the ancient erosion surfaceHow can rock units be traced from one area to another Correlationdetermining time equivalency of rock units rock units may be correlated within a region a continent and even between countries Physical Continuitybeing able to physically visually follow a rock unity between two placesSimilarity of Rock Typessame sequence of rocks Tillitesglacially deposited sedimentary rock Key beda very distinctive layerCorrelation by Fossils Paleontologistspecializes in the study of fossilsFaunal succession William Smitha principle or law stating that fossil species succeed one another in a definite and recognizable order in general fossils in progressively older rock show increasingly greater differences from species living at present Index fossila fossil from a very shortlived geographically widespread species known to exists during a specific period of geological timeFossil assemblagevarious different species of fossils in a rock layerHow do we use Relative Dating to Understand Geological Time The Standard Geologic Time Scalea worldwide relative time scale based on fossil assemblagesRelative time scale 3 eras which are subdivided into periods which are subdivided into epochsPrecambrianthe vast amount of time that preceded the Paleozoic EraPaleozoic Era old life began with the appearance of complex life as indicated by fossilsMesozoic Era middle lifedinosaurs became the dominant animals Cenozoic Era new lifeoQuaternary Periodthe youngest geologic period includes present time Pleistocene Epochan epoch of the Quaternary Period characterized by several glacial agesHolocene Epoch RecentHow can we determine the absolute age of rocks Oldest rock from northwest Canada403 billion years old
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