1Fossils: evidence of past lifeRemains or traces of prehistoric lifePetrifiedCavities and pores are filled with precipitated mineral matterPetrifiedFormed by replacementCell material is removed and replaced with mineral matterMoldShell or other structure is buried and then dissolved by underground waterunderground waterShape is preserved in the surrounding sedimenthttp://www.ammonoid.com/Manning.htmlCast Hollow space of a mold is filled with mineral matter CarbonizationOrganic matter becomes a thin residue of carbon. This is a ‘compression’ of the original organismImpressionReplica of the fossil's surface preserved in fine-grained sedimenthttp://www.lfbuffalo.org/exhibitions/map/t/Preservation in amberHardened resin of ancient trees surrounds an organismIndirect Evidence Includes• Tracks• Burrows• Coprolites – fossil dung and stomach contents• Gastroliths – stomach stones used to grind food by some extinct reptiles2TracksDinosaur footprint in fine-grained limestone near Tuba City, Arizona. Types of fossils• Petrified• Formed by lt• Carbonization • Impressionreplacement •Mold•Cast• Preservation in amber• Indirect evidence Conditions favoring preservation• Rapid burial• Possession of hard partsFossils and correlation• Principle of faunal succession• Index fossilsPrinciple of faunal succession• Proposed by William Smith – late 1700s• Fossil organisms succeed one another in a definite and determinable orderand determinable order, therefore any geologic time interval can be recognized by its fossil contenthttp://www.lfbuffalo.org/exhibitions/map/a/Archean through Devonianhttp://rst.gsfc.nasa.gov/Sect2/Sect2_1b.htmlCarboniferous through Quaternaryhttp://rst.gsfc.nasa.gov/Sect2/Sect2_1b.htmlCambrian Marine Lifehttp://www.handprint.com/PS/GEO/geoevo.htmlTrilobitehttp://www.ststephens.it/biology/fossils.html3Ordovician Invertebrateshttp://www.handprint.com/PS/GEO/geoevo.htmlCrinoid—380 mahttp://www.lsa.umich.edu/exhibitmuseum/exhibits/temporary_exhibits/Ordovician sea floorhttp://www.uwsp.edu/geo/faculty/hefferan/Geol106/CLASS6/MAIN%20PAGE.htmSilurian reef• Silurian Reefhttp://hoopermuseum.earthsci.carleton.ca/camex/1rpaleoreef.htmlSilurian Landscapehttp://www.nasa.gov/worldbook/earth_worldbook.htmlDevonian Seahttp://www.handprint.com/PS/GEO/geoevo.htmlMid Paleozoichttp://www.tufts.edu/as/wright_center/cosmic_evolution/docs/text/text_bio_4.htmlLate Paleozoichttp://www.tufts.edu/as/wright_center/cosmic_evolution/docs/text/text_bio_4.htmlCarboniferous Fern Forestshttp://www.handprint.com/PS/GEO/geoevo.html4Permian Seahttp://www.handprint.com/PS/GEO/geoevo.htmlPermian Reptileshttp://www.handprint.com/PS/GEO/geoevo.htmlPermian Extinction• Link to hypotheses of the Permian Extinction• 80-95% of marine species died out70% f t t i l t b thttp://en.wikipedia.org/wiki/Permian_extinction•70%+ of terrestrial vertebrates• Largest extinction episode in geologic recordGeologic time scale• Divides geologic history into units• Originally created using changes in organisms representing that time intervalintervalSubdivisions• Eons–Eras• Periods–EpochsEonGreatest expanse of time: 4 eons• Phanerozoic ("visible life") – the most recent eon: started 543 Ma• Proterozoic: 2500 – 543 Ma• Archean: 3800 – 2500 Ma• Hadean – oldest eon 4500–3800 MaEras of the Phanerozoic eon• Cenozoic ("recent life"): 65 Ma – now • Mesozoic ("middle life"): 248 – 65 Ma• Paleozoic ("ancient life"): 543 – 248 MaGeologic Time Scale Mesozoichttp://geography.berkeley.edu/ProgramCourses/CoursePagesFA2002/Geog40/Geog40.Week7.html5Mesozoichttp://serc.carleton.edu/introgeo/earthhistory/dinosaur.htmlMesozoichttp://geography.berkeley.edu/ProgramCourses/CoursePagesFA2002/Geog40/Geog40.Week7.htmlMesozoichttp://www.tufts.edu/as/wright_center/cosmic_evolution/docs/text/text_bio_4.htmlArcheopteryxhttp://www.researchcasting.ca/sculpt%20miami.htmMesozoic Mammal• Eomaiahttp://www.amnh.org/exhibitions/dinosaurs/diorama/Mesozoic Mammal• Repenomamushttp://www.amnh.org/science/papers/mesozoic_mammal.phpJurassichttp://www.worldbook.com/features/dinosaurs/html/world_mesozoic.htmlCretaceoushttp://www.worldbook.com/features/dinosaurs/html/world_mesozoic.htmlMesozoic Seahttp://geography.berkeley.edu/ProgramCourses/CoursePagesFA2002/Geog40/Geog40.Week7.html6Mesozoic seahttp://www.uky.edu/AS/Geology/webdogs/time/mesozoic/mesozoic.htmCretaceous Extinction• Perhaps 60% of species died• Result of radical change in environment• Perhaps Earth encountered a large titmeteorite—– 10 km in diameter– 90,000 km/hr– Equivalent to 100 megatons of TNT explodingCenozoic mammalshttp://www.handprint.com/PS/GEO/geoevo.htmlCenozoichttp://www.handprint.com/PS/GEO/geoevo.htmlCenozoichttp://www.uky.edu/AS/Geology/webdogs/time/cenozoic/cenozoic.htmCenozoichttp://www.copyrightexpired.com/Heinrich_Harder/cenozoic.htmlRelative dating Placing rocks and events in proper sequence of formationDeciphering Earth’s history from clues in the rocksthe rocksLateral Continuityhttp://cse.cosm.sc.edu/hses/RelatDat/pages/lateral.htmPrinciple of Original Horizontality • Sediment is deposited horizontally http://faculty.icc.edu/easc111lab/labs/labf/orig_horizontality.jpg7• Oldest rock A• Younger rocks aboveEi thPrinciple of Superposition•E is the youngesthttp://cse.cosm.sc.edu/hses/RelatDat/pages/superpos.htmPrinciple of Cross-cutting Relationships• Younger feature cuts through an older feature – Something must exist first to be cut by another thinganother thing• The ‘things’ cutting may be ‘things’, such as igneous intrusions• Or they may be events, like fault breaks, folding, or erosion periodsCross-cutting relationshipsFolding occurred after depositionhttp://rst.gsfc.nasa.gov/Sect2/Sect2_6.htmlUnconformitiesA break in the rock record • Three types of unconformities • Angular unconformity –• Disconformity – strata on either side are parallel • NonconformityAngular Unconformity• Tilted rocks are overlain by flat-lying rocks• Remember the principle of original horizontality?Formation of an angular unconformityunconformitySimple angular unconformityhttp://www.grisda.org/colorado/index.htmFolding, erosion, deposition, foldinghttp://rst.gsfc.nasa.gov/Sect2/Sect2_6.html8Nonconformity• Metamorphic or igneous rocks below • Younger sedimentary rocks above NonconformityDisconformity• Gap in sedimentation that may have erosion also• Represents
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