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1Unit1BasicGeologyLesson1GeologyEarthscience(alsoknownasgeoscience,thegeosciencesortheEarthsciences),isanall-embracingtermforthesciencesrelatedtotheplanetEarth.Itisarguablyaspecialcaseinplanetaryscience,theEarthbeingtheonlyknownlife-bearingplanet.TherearebothreductionistandholisticapproachestoEarthsciences.TheformaldisciplineofEarthSciencesmayincludethestudyoftheatmosphere,oceansandbiosphere,aswellasthesolidearth.Geologyisgenerallycategorizedwithinthegeosciences.Geology(fromtheGreek，geo,earthand,logos,speech)isanaturalscience,whichstudiesthegeologyscienceoftheearth'shistory,composition,andstructure,andtheassociatedprocesses.Itdrawsuponchemistry,biology,physics,astronomy,andmathematics(notablystatistics)forsupportofitsformulations.Geologyisaverycomplexscience.TherearemanybranchesofGeology,whichcanbegroupedunderthemajorheadingsofphysicalandhistoricalgeology.PhysicalGeologyPhysicalgeologyincludesmineralogy,thestudyofthechemicalcompositionandstructureofminerals;petrology,thestudyofthecompositionandoriginofrock;geomorphology,thestudyoftheoriginoflandformsandtheirsmodificationbydynamicprocesses;geochemistry,thestudyofthechemicalcompositionoftheearthmaterialsandthechemicalchangesthatoccurwithintheearthandonitssurface;geophysics,thestudyofthebehaviorofrockmaterialsandinresponsetostressesandaccordingtotheprinciplesofphysics;sedimentology,thescienceoftheerosionanddepositionofrockparticlesbywind,water,orice;structuralgeology,thestudyoftheforcesthatdeformtheearth’srocksandthedescriptionandmappingofdeformedrockbodies;economicgeology,thestudyoftheexplorationandrecoveryofnaturalresources,suchasoresandpetroleum;andengineeringgeology,thestudyoftheinteractionoftheearth’scrustwithhuman-madestructuressuchastunnel,mines,dams,bridges,andbuildingfoundations.HistoricalgeologyHistoricalgeologydealswiththehistoricaldevelopmentoftheearthfromthestudyofitsrocks.Theyareanalyzedtodeterminetheirstructure,composition,andinterrelationshipsandareexaminedforremainsofpastlife.Historicalgeologyincludespaleontology,thesystematicstudyofpastlifeforms;stratigraphy,oflayeredrocksandtheirinterrelationships;paleogeography,ofthelocationsofancientlandmassesandtheirboundaries;andgeologicmapping,thesuperimposingofgeologicinformationuponexistingtopographicmaps.Historicalgeologistsdividealltimesincetheinformationoftheearliestknownrocks(c,4billionyearsago)intofourmajordivisions:thePrecambrian,Paleozoic,Mesozoic,andCenozoiceras.Each,excepttheCenozoic,endedwithprofoundchangesinthedispositionoftheearth’scontinentsandmountainsandwascharacterizedbytheemergenceofnewformsoflife.Broadcyclicalpatterns,whichrunthroughallhistoricalgeology,includeaperiodofmountainandcontinentbuildingfollowedoneoferosionand,inturn,byanewperiodofelevation.EarlyGeologicStudiesObservationsonearthstructureandprocessesweremadebyanumberoftheancients,includingHerodotus,Aristotle,Lucretius,Strabo,andSeneca.Theirindividualeffortsinthe2naturalhistoryoftheearth,however,providednosustainedprogress.Theirmajorcontributionisthattheyattributedthephenomenatheyobservedtonaturalandnotsupernaturalcauses.ManyoftheideasexpressedbythesemenwerenottoresurfaceuntiltheRenaissance.LaterLeonardodaVincicorrectlyspeculatedonthenatureoffossilsasremainofancientorganismsandontherolethatriversplayintheerosionofland.Agricolamadeasystematicstudyoforedepositsintheearly16thcentury.RobertHookeandNicolausStenobothmadepenetratingobservationsonthenatureoffossilsandsediments.EvolutionofModernGeologyModerngeologybeganinthe18thcentury,whenfieldstudiesbytheFrenchmineralogistJ.E.Guttardandothersprovedmorefruitfulthanspeculation.TheGermangeologistAbrahamGottlobWerner,inspiteofthemanyerrorsofhisspecificdoctrinesandthediversionofmuchofhisenergyintoafruitlesscontroversy(inwhichhemaintainedthatoriginofallrockswasaqueous),performedagreatserviceforthesciencebydemonstratingthechronologicalsuccessionofrocks.In1795theScottishgeologistJamesHuttonlaidthetheoreticalfoundationformuchofthemodernsciencewithhisdoctrineofuniformitarianism,firstpopularizedbytheBritishJohnPlayfair.LargelythroughtheworkofsirCharlesLyell,thisdoctrinereplacedtheopposingoneofcatastrophism.Geologyinthe19thcenturywasinfluencedalsobytheworkofCharlesDarwinandenrichedbytheresearchesoftheSwiss-AmericanLouisAgassiz.Inthe20thcentury,geologyhasadvancedatanever-increasingpace.Theunravelingofthemysteryofatomicstructureandthediscoveryofradioactivityallowedprofoundadvancesinmanyphasesofgeologicresearch.ImportantdiscoveriesweremadeduringtheInternationalGeologicalYear(1957-58),whenscientistsfrom67nationsjoinedforceininvestigatingproblemsinallbranchesofgeology.Thesystematicsurveyoftheearth’soceansbroughtradicalchangesinconceptsofcrustalevolution.Asaresultofnumerousflybyspacecraft,geologicalstudieshavebeenextendedtoincluderemotesensingofotherplanetsandsatellitesinthesolarsystemandthemoon.Laboratoryanalysesofrockssamplesbroughtbackfromthemoonhaveprovidedinsightintotheearlyhistoryofnear-earthspace.On–siteanalysesofMartiansoilsamplesandphotographicmappingofitssurfacehavegivencluesaboutitscompos