Geologic age determination
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Geologic Age Determination. http://www.nps.gov/archive/grca/photos/images/T501.jpg. Uniformitarianism: (uniform = the same) Geological processes occurring today, like plate movement, mountain formations, etc., have been occurring since the Earth was formed.

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Geologic Age Determination

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Geologic age determination

Geologic Age Determination

http://www.nps.gov/archive/grca/photos/images/T501.jpg


Geologic age determination

Uniformitarianism: (uniform = the same) Geological processes occurring today, like plate movement, mountain formations, etc., have been occurring since the Earth was formed.

Correlation: The matching of equivalent rocks in different geographic areas.

http://earthsci.org/processes/geopro/introgeo/rockcycle.gif


Geologic age determination

Geological Views of Time

  • Relative time– Places geologic events in order of occurrence. Determining relatively how old rock units are based upon the rocks that surround it. What happened first? What happened last? These subdivisions of the geologic time scale are given names based on places where particular rocks were first described.

  • (Example: Any teacher in this school is “older” relative to the students no matter how old the teachers actually are)

http://www.geo.ucalgary.ca/~macrae/timescale/timescale.html


Geologic age determination

Geological Views of Time

  • Absolute time -- Numerical ages in "millions of years ago". These dates are most commonly obtained from radiometric dating methods using carefully chosen rock samples.

  • (Example: Most students in my sophomore Ecology class are 16 years old, while I am 24 years old)

http://www.geo.ucalgary.ca/~macrae/timescale/timescale.html


Geologic age determination

Geologic Timescale


Geologic age determination

http://www.geo.ucalgary.ca/~macrae/timescale/timescale.html


Geologic age determination

Law of Superposition

The Law of Superposition is one of the most basic principles of geology . Younger rock layers are deposited on top of older layers, during normal conditions of deposition. The basic principle of stratigraphy (the study of sedimentary rock layers), is still the single best method that geologists have for determining the relative ages of rock sequences.

http://www.astro.virginia.edu/class/oconnell/astr121/im/GrandCan-geolog-column.jpg


Geologic age determination

Notice the different color bands that indicate different layers of rock.


Geologic age determination

Principle of Original Horizontality

Sedimentary rock layers (and lava flows) are always formed in a horizontal orientation. Any folding or tilting must have happened sometime after the layers were originally formed.

http://www.canyondave.com/Layers.html

http://www.cacegypt.org/Sinai/homework/GREG/pages/Q2_04/Q2Images/PlateTec_Pics/foldMnt.jpg


Geologic age determination

BeforeAfter

**If there is any folding, tilting, or faulting, you know that it occurred after the rock was layered because of the Principle of Original Horizontality


Geologic age determination

Cross-Cutting

The Principle of Cross-Cutting Relationshipsstates that an igneous intrusion (or a fault) is always younger than the rock it cuts across.

http://www.litho.ucalgary.ca/transect_info/snorcle/photos/granite.html

http://ceed.utpb.edu/media/images/west-texas-geology/1ig_chisosdikes.jpg


Geologic age determination

Gneiss in Granite

http://www.msstate.edu/dept/geosciences/CT/TIG/WEBSITES/LOCAL/Summer2003/Schuster-Loomis_Rea/gneiss%20black%20inclusions.jpg

http://www.gpc.edu/~pgore/geology/historical_lab/relativedating.htm

The Principle of Inclusionsstates that the rock unit that contains inclusions is younger than the rock that the inclusions came from.

In the diagram at the left, the igneous intrusion (E) must be younger than rock layers A, B, C, and D because it contains inclusions from those layers.


Geologic age determination

  • Which is older, the fault or the rock?


Geologic age determination

From oldest to youngest:

E

C

B

D

A


Geologic age determination

  • C

  • A

  • L

  • B

  • G

  • F


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