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Geologic time Relative dating

Interpreting Earth’s Rocks to Determine Its Past History. Geologic time Relative dating. Geologic Time. Relative Dating - sequence of geologic events in a region (order of past events) How do we know how old something is?. Law of Superposition. Oldest layer on bottom (if undisturbed).

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Geologic time Relative dating

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  1. Interpreting Earth’s Rocks to Determine Its Past History Geologic timeRelative dating

  2. Geologic Time • Relative Dating - sequence of geologic events in a region (order of past events) • How do we know how old something is?

  3. Law of Superposition • Oldest layer on bottom (if undisturbed) http://www.angelfire.com/az3/mohgameil/Layering4.jpg

  4. The Grand Canyon http://www.calstatela.edu/faculty/acolvil/sediment/superposition.jpg

  5. Principle of Original Horizontality • Sediments are originally deposited as horizontal (or near horizontal) beds Use for tilted or bent layers

  6. POH • What can cause rock to bend?

  7. folded rock layers = compression by tectonic activity

  8. Cross-Cutting Relationships • An igneous intrusion (or fault) is younger than the rock layers that it cuts across. These are younger than the surrounding rock youngest fault oldest

  9. Cross-Cutting Relationships Igneous dike is younger than the marble layer it cuts across.

  10. Cross-Cutting Relationships 6 is younger than1, 2, or 3 because it cuts across them!

  11. Law of inclusions • The inclusion is older than the rock it is in • Rock type?

  12. practice

  13. Which pair is older?Which law is used? A & B _________________ D & M _________________ D & E _________________J & K _________________

  14. James Hutton: The father of modern geology (1726-1797) Uniformitarianism: processes acting on earth today (volcanism, erosion, plate tectonics, etc.) have done so in the past “The present is the key to the past.” Basis of relative dating

  15. Unconformities = “Missing Time”

  16. Angular Unconformities • Folded layers below horizontal layers. rock layers are eroded new horizontal layers are deposited angular unconformity (rock layers have been eroded away)

  17. Angular Unconformity sedimentary rocks above and below unconformity surface with rocks below tilted at an angle F E D C B A

  18. Nonconformity – younger sedimentary rocks rest on older igneous rocks sedimentary rock layers Cambrian Precambrian Granite

  19. Nonconformity

  20. Disconformity DISCONFORMITY:Missing rock layers (sedimentary) Very hard to pick out

  21. Disconformities

  22. Type of unconformity?

  23. Siccar Point, Scotland

  24. limestone shale sandstone granite http://www.env.duke.edu/eos/geo41/st013.gif

  25. http://www001.upp.so-net.ne.jp/fl-fg/06-02.htm

  26. http://spot.pcc.edu/~mhutson/160/shore_acres.jpg

  27. Resources • http://courses.geo.ucalgary.ca/glgy209L03/docs/Lecture15_GLGY209_six.pdf • http://perth.uwlax.edu/faculty/stoelting/Intro/Guides/Images2/law_of_superposition_b.jpg • http://www.science.sjsu.edu/scied/255/ppt/superposition/img025.jpg • http://www.gpc.peachnet.edu/~jsummero/Cross-cutting-a.jpg • http://www.gc.maricopa.edu/appliedscience/gjc-nsf/images/CRH0204.JPG • http://maverick.gc.maricopa.edu/appliedscience/gjcweb/geomap/images/ang.unconf.jpg • http://www.geog.ouc.bc.ca/physgeog/contents/images/hutton.jpg • http://www.bigbendpaleo.com/Photo%20Gallery/Big%20Bend%20Region,%20Texas/Big%20Bend%20National%20Park%20-%20Syncline%20-%20Javalina%20Creek%20-%2020%20June%201995.jpg • http://geoimages.berkeley.edu/GeoImages/Johnson/Images/Large/CD3/028.jpg • http://www.vvdailypress.com/travel/rainbow/images/rock.jpg • http://academic.emporia.edu/aberjame/struc_geo/folds/fold06.jpg • http://www.geology.pitt.edu/images/folds.jpg • http://faculty.evansville.edu/de3/b39902/PPoint/Geologic%20Time/img007.jpg • http://www.photo.net/photo/pcd2882/grand-canyon-region-aerial-85.3.jpg • http://www.cowanstark.com/horsehoe-bend.jpg • http://home.flash.net/~alanm52/Cross_cutting.jpg • http://www-class.unl.edu/geol101i/images/igneous%20images/Black%20Canyon%20Gunnison.jpg • http://freespace.virgin.net/craven.pendle/stratigraphy/unconformity.jpg

  28. http://comp.uark.edu/~sboss/siccar.jpg • http://www.pittstate.edu/services/scied/Teachers/Field/Camp/Us67-1/us67cut.jpg • http://maverick.gc.maricopa.edu/appliedscience/gjcweb/geomap/images/MW8-11.jpg • http://www3.uakron.edu/geology/Foos/parks/rmgcan2.html • http://www.ldeo.columbia.edu/edu/dees/ees/ies2/slides/disconformity.gif • http://geology.lssu.edu/NS102/images/figure%2009-06.gif • http://www.crienterprises.com/C-Assets/J-Hanifa-Unconf-W-Birk.jpg • http://www.uoguelph.ca/~sadura/stgref/stg32b.gif • http://www.geo-outdoors.info/images/eye_protection.jpg • http://enterprise.cc.uakron.edu/geology/natscigeo/Lectures/time/gtime1.htm

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