Geologic Time Chapter 21 Rock cycle diagram Leaves of History Modern geology Uniformitarianism Fundamental principle of geology The present is the key to the past Relative dating 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 Nicolaus Steno 1636 1686 1669 work relates to deposition of sediment http www ucmp berkeley edu history steno html Principle of 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 Principle of Original Horizontality Sediment is deposited horizontally http faculty icc edu easc111lab labs labf orig horizontality jpg Lateral Continuity http cse cosm sc edu hses RelatDat pages lateral htm Lateral Continuity Principles of Relative Dating Principle of original horizontality Principle of lateral continuity Principle of superposition Principle of cross cutting relationships Principle of 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 Cross cutting relationships Folding occurred after deposition http rst gsfc nasa gov Sect2 Sect2 6 html Principles of Relative Dating Principle of original horizontality Principle of lateral continuity Principle of superposition Principle of cross cutting relationships Principle of inclusion Inclusions One rock contained within another Rock containing the inclusions is younger than the one the inclusions are derived from How inclusions form Formation of Inclusions The fragments are included with the deposition of rock on top of the weathered surface 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 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 Unconformities A break in the rock record Three types of unconformities Angular unconformity Disconformity strata on either side are parallel Nonconformity Angular Unconformity Tilted rocks are overlain by flat lying rocks Remember the principle of original horizontality Formation of an angular unconformity Simple angular unconformity http www grisda org colorado index htm Folding erosion deposition folding http rst gsfc nasa gov Sect2 Sect2 6 html Nonconformity Metamorphic or igneous rocks below Younger sedimentary rocks above Nonconformity Disconformity 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 Relative Dating Exercise F youngest crosscutting relationships D crosscutting relationship and inclusions A superposition B superposition C superposition E oldest superposition on bottom http www winona edu geology MRW maps htm Principles of Relative Dating Principle of original horizontality Principle of lateral continuity Principle of superposition Principle of cross cutting relationships Principle of inclusion Principle of faunal succession Fossils evidence of past life Remains or traces of prehistoric life Types of fossils Petrified Formed by replacement Mold Cast Carbonization Impression Preservation in amber Indirect evidence Petrified Cavities and pores are filled with precipitated mineral matter Petrified Formed by replacement Cell material is removed and replaced with mineral matter Mold Shell or other structure is buried and then dissolved by underground water http www ammonoid com Manning html Shape is preserved in the surrounding sediment Cast Hollow space of a mold is filled with mineral matter Carbonization Organic matter becomes a thin residue of carbon This is a compression of the original organism Impression Replica of the fossil s surface preserved in fine grained sediment http www lfbuffalo org exhibitions map t Preservation in amber Hardened resin of ancient trees surrounds an organism Indirect Evidence Includes Tracks Burrows Coprolites fossil dung and stomach contents Gastroliths stomach stones used to grind food by some extinct reptiles Tracks Dinosaur footprint in fine grained limestone near Tuba City Arizona Conditions favoring preservation Rapid burial Possession of hard parts Fossils and correlation Principle of faunal succession Index fossils Principle of faunal succession Proposed by William Smith late 1700s Fossil organisms succeed one another in a definite and determinable order therefore any geologic time interval can be recognized by its fossil content http www lfbuffalo org exhibitions map a Geologic Time Scale Archean through Devonian http rst gsfc nasa gov Sect2 Sect2 1b html Carboniferous through Quaternary http rst gsfc nasa gov Sect2 Sect2 1b html Cambrian Marine Life http www handprint com PS GEO geoevo html Trilobite http www ststephens it biology fossils html Crinoid 380 ma http www lsa umich edu exhibitmuseum exhibits temporary exhibits Ordovician sea floor http www uwsp edu geo faculty hefferan Geol106 CLASS6 MAIN 20PAGE htm Ordovician Invertebrates http www handprint com PS GEO geoevo html Silurian reef Silurian Reef http hoopermuseum earthsci carleton ca camex 1rpaleoreef html Silurian Landscape http www nasa gov worldbook earth worldbook html Devonian Sea http www handprint com PS GEO geoevo html Mid Paleozoic http www tufts edu as wright center cosmic evolution docs text text bio 4 html Late Paleozoic http www tufts edu as wright center cosmic evolution docs text text bio 4 html Carboniferous Fern Forests http www handprint com PS GEO geoevo html Permian Sea http www handprint com PS GEO geoevo html Permian Reptiles http
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