Chapter 1 - An Introduction to Geology.pptx - Physical...

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PhysicalGeologyGEOL1403An Introduction to Geology1Welcome to GEOL 1403!These Powerpoint slide shows should be usedalongwith your textbook readingsBe careful not to get behind in your readingduringthe semester
2The Science of GeologyTraditionally an introduction to geologyisdivided into two classes:Physical Geology (the class you are taking)– Historical GeologyPhysicalGeologyExamines the materials which make up the Earthandthe processes by which they form and changeHistoricalGeologyExplores the origin of the Earth and itsdevelopmentthrough time
A fundamental principle ofgeology is basedon thisobservation:The processes operating in Earth systemstodayhave operated in a similar mannerthroughoutmuch of geologic timeIt is often expressed by the phrase “Thepresentis the key to the past”This idea was first published by the eighteenthcentury geologist James HuttonJames Hutton, “FatherofModernGeology”Siccar Point, Scotland3
4Before Hutton and his colleagues, people believedthatthe Earth was only a few thousand years oldThey explained geological features as the resultsofimmense catastrophesThey thought that these events occurred during the pastwhenthe world operated under quite different conditionsThis viewpoint, termed “Catastrophism,” prevailedamong evenserious scientists until the late 18thcenturyHutton wrote, “The past history of our globe mustbeexplained by what can be seen to be happeningnow:"Water sculpted the surface of EarthErosional detritus was carried from the land to the seaSediments were compacted into layered rocksThen, by the action of enormous forces, the rock layerswereuplifted to form new landThis view came to be known as thePrinciple ofUniformitarianism
Catastrophism vs.UniformitarianismRational thinking took hold during theEnlightenment(late eighteenth century = late1700’s)The true age of the Earth came into questionInvestigators like James Hutton argued that theEarthwas very oldIn pursuing the question ofEarth’s true age, Huttonpioneered or anticipatedmanyaspects of moderngeology:Plate Tectonic theoryThe Rock CycleStratigraphyEarth System ScienceDeep TimeHe reallywasthe Father ofModern Geology!5
6Geologic TimeThere are two basic approaches to time:The older of the two deals with time in aRELATIVEsense(order or sequence of rocks or events regardlessof theamount of time involved)Uses physical characteristics and positions of rocks todetermineage of rockThis approach was developed by the old-time geologists –likeJames HuttonThe more recently developed approach has been todealwith geologicaltime ina numerical orquantitative sense,termed ABSOLUTE time:Uses radiometric or other finite methods of datingProduces ages in terms of numbers of yearsNot all rocks can be directlydated by absolute methods

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