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Interpreting Earth’s Rocks to Determine Its Past History

Explore the fascinating world of geologic time, from relative to absolute dating methods, with a focus on key concepts like superposition and unconformities. Unravel the mysteries of Earth's past through the eyes of geologists, akin to CSI detectives. Delve into principles such as original horizontality and cross-cutting relationships to piece together the intricate puzzle of our planet's history.

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Interpreting Earth’s Rocks to Determine Its Past History

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

  2. Geologic Time • Relative Time - sequence of geologic events in a region (order of past events) • Absolute Time – numeric- time in years; use radioactive isotopes. • How do we know how old something is?

  3. James Hutton: The father of modern geology (1726-1797) Uniformitarianism: “The present is the key to the past.”

  4. Examples of uniformitarianism • Petoskey stones and past climates • How sandstone forms Grand Canyon formation • Dino reconstruction

  5. Determining Geologic History: Geologists are like CSI detectives wanting to know Where?, When?, Why?, How? Sometimes very little “evidence” remains (exposure, erosion) Evidence has been moved or tampered with! Rocks have been moved (faults, folds) Usually no witnesses!

  6. Principle of Superposition • Oldest layer on bottom (if tectonically undisturbed) Younger Older http://www.angelfire.com/az3/mohgameil/Layering4.jpg

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

  8. Principle of Original Horizontality • Sediments are originally deposited as horizontal (or near horizontal) beds- use with folded layers .

  9. folded rock layers = compression by tectonic activity

  10. 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

  11. Write the order of events that have taken place above. List (oldest - 1 to youngest - 6)

  12. Which came first? A B C D E Order the rock layers above from oldest to youngest. Is this an example of absolute or relative dating?

  13. Which came first? A C B C D B D D E The first layer deposited and the oldest is D, followed by C, A, B, and E.

  14. List the order of events that took place: earthquake deposit D deposit B deposit G intrusive lava rocky deposit R river cuts through deposit E deposit A

  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. The Great Unconformity – Grand Canyon, AZ

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

  20. Nonconformity

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

  22. Disconformities

  23. Siccar Point, Scotland

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

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

  26. 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

  27. 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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