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Geologic Time. Law of SuperPosition. Super what??!?!. Superposition: Younger rock layers are on top of older rock layers. Used with the other principles of stratigraphy to study rock layers and layering.
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Geologic Time Law of SuperPosition
Super what??!?! • Superposition: Younger rock layers are on top of older rock layers. • Used with the other principles of stratigraphy to study rock layers and layering. • Stratigraphy : “Branch of geology concerned with the study of the formation, composition, ordering in time, and arrangement in space of stratified rocks.” – USGS • Nicolaus Steno (1669) http://stloe.most.go.th/html/lo_index/LOcanada8/801/2_en.htm
Principles of Stratigraphy • superposition - in a vertical sequence of sedimentary or volcanic rocks, a higher rock unit is younger than a lower one. "Down" is older, "up" is younger. • horizontality - rock layers were originally deposited close to horizontal. • Original lateral extension - A rock unit continues laterally unless there is a structure or change to prevent its extension. • cross-cutting relationships - a structure that cuts another is younger than the structure that is cut. • inclusion - a structure that is included in another is older than the including structure. • "uniformitarianism" - processes operating in the past were constrained by the same "laws of physics" as operate today • http://www.talkorigins.org/faqs/dating.html :
Inclusion Original lat. Ext. Cross Cutting
Animations • Disconformity : http://duedall.fit.edu/wholeearth/PHysical%20geology%20animations/0012.swf • Geologic history http://www.wwnorton.com/college/geo/earth2/content/chapter_12/animations.asp#12_1
Rock Layer Formation • Sedimentary: igneous rock that is broken down by weathering into fine particles. Compressed over time by it’s own weight and weight of layers above
Rock Layer Formation • Igneous: formed from liquid hot magma that cools above or below the earths surface.
Were are fossils found • Sedimentary rock -- yes, Most fossils are found in sedimentary rocks as an animal dies it get’s buried by sediment , perhaps along a river or lake bed, and the organic parts of the animal are replaced by minerals in the water/sediment that • Igneous rock -- nope, Fossils aren’t found in igneous rock because remember that igneous rock starts out as molten lava and if an animal were to be covered by it then it would melt or burn away.
How old are fossils? • 2 Generic Methods: • Absolute • Several methods. • (radiometric) Measurement of the decay rate of isotopes. • Carbon 14 : 5730 years Dates organic material • Potassium – Argon : 50,000 to 2 billion years ago Dates volcanic material • Relative • Uses igneous rock above or below sedimentary rock to determine age.
Which layers are Sedimentary/Igneous? • S: 1,2,3,4,5,7,8,11,12 • I: 10,8,6 • Which layers are older? • 1 - 12 • What is a possible history for this area? • 1-5 area was covered by an ocean • 7 - Oceans recede, area appears to be covered by large amounts of plant life • 9 small to mid size animals appear • 11,12 larger animals appears
Resources • http://www.usgs.gov/ • http://jersey.uoregon.edu/~mstrick/AskGeoMan/geoQuerry13.html • Wiki Sedimentary -- http://en.wikipedia.org/wiki/Sedimentary_rock • http://www.talkorigins.org/faqs/dating.html • http://www.pbs.org/wgbh/evolution/library/03/3/l_033_01.html • http://pubs.usgs.gov/gip/geotime/time.html <- curvy geotime • http://www.kidsgeo.com/geology-for-kids/0030-geologic-time.php • http://stloe.most.go.th/html/lo_index/LOcanada8/801/3_en.htm • “Geology an introduction to physical geology” , Chernicoff & Whitney, ISBN 0-13-147464-1 , Page 20 • “Geology an introduction to physical geology” , Chernicoff & Whitney, ISBN 0-13-147464-1 , Page 234
