Cochise College Student Papers in Geology
Geology Home Page physical geology historical geology
Roger Weller, geology instructor regional geology planetary gems
wellerr@cochise.edu
Grand Canyon
Jonathan Holmes
Historical Geology
Spring 2008
The Grand Canyon and The Geological Time Scale
The Grand Canyon is a beautiful, natural monument to the immense power of
nature.
Many flock to see its amazing geological construct, but beyond the beauty of it
all: is there anything it can teach us?
http://www.geo-images.com/twds2.jpg
Historical Geology
History
could easily be considered, in the most basic of senses, a study of the past.
Therefore, historical geology, at the roots, is the study of the geological
landscape of the past. But how do we know what the Earth was like ten million,
one-hundred million, or even a billion years ago? The answer, geologists say, is
in the rock layers beneath us.
Radioactive Age Dating
Through
radioactive age dating, scientists can, within a relative period of time, assign
dates to rocks by analyzing the amount of a radioactive isotope within the rock
and comparing that number to the isotope’s known rate of decay. Although this
paper will not delve into the specifics of radioactive age dating, there are
many different sources of information on this topic. A good source can be found
at the following link:
http://www.tulane.edu/~sanelson/eens211/radiometric_dating.htm.
The Geological Time Scale
The Geological Time Scale (hereafter referred to as GTS) is a scale, of course, which reveals the common names of the respective common names for the time periods of the Earth and their relative age to today’s date. The dating is not set by a certain amount of time like a week is, i.e.: seven days; rather, by specific events in the past as exposed by the GTS. The following chart is a nice way of viewing how old the different layers of the Earth are in relation to modern time. On a side note, Humans came into existence in the Quaternary Period. “Finer subdivisions of time are possible and the periods of the Cenozoic are frequently subdivided into epochs. Subdivision of periods into epochs can be done only for the most recent portion of the geologic time scale.” http://geology.com/time.htm
Geologic Time Scale
A Time Line for the Geological Sciences
Although this information is the most current and up-to-date
information the scientific community can provide, there are some who would wish
to reject this information on the basis that this is not an accurate description
of the layers of the Earth. By closely examining the Grand Canyon of Arizona,
USA, one can see how the GTS can be found in nature.
The Grand Canyon
How it was made
Although
there is no known actual reason for how the Grand Canyon was formed, the most
educated hypothesis is erosion which would, of course, require an extensive
period of time to cause such an enormous hole.
The Layers of Rock in The Grand Canyon
The primary
layers of rock in the Grand Canyon are individually labeled and dated. The names
are: Kaibab Limestone, Toroweap Formation, Coconino Sandstone, Hermit Shale,
Supai Formation, Redwall Limestone, Muav Limestone, Bright Angel Shale, Tapeats
Sandstone, and Vishnu Schist.
Here is an actual picture of the Grand Canyon with the names of the layers
pointed out.
http://www.bobspixels.com/kaibab.org/geology/gc_geol.htm
For further clarification, these are not the same names as found in the GTS as the GTS is a dating scale; these are the specific names of these rock layers of only the Grand Canyon.
Radioactive age dating has been used to scientifically determine the age of these layers.
Kaibab Limestone – Approximately 250 million years. Mainly sandy limestone. Thin layers of sandstone or shale sometimes appear. Color is usually creamish to grayish-white.
Toroweap Formation – Approximately 255 million years. Same rocks as Kaibab Limestone only with slightly darker coloring.
Coconino Sandstone – Approximately 260 million years. Compiled of pure quartz sand. Same color as the Kaibab Limestone.
Hermit Shale – Approximately 265 million years. Made from soft, rust-colored shale which has eroded into a slope.
Supai Formation – Approximately 285 million years. Thin layer of sandstone on top of a layer of shale mingled with a little bit of limestone. Sandy colored on top and red on the bottom.
Redwall Limestone – Approximately 335 million years. Comprised of marine limestone and dolomites, a white, reddish, or greenish mineral consisting of calcium magnesium carbonate.
Mauv Limestone – Approximately 515 million years. Mainly made of limestone layers with layers of sandstone and shale in between. Grey in color.
Bright Angel Shale – Approximately 530 million years. Composed of Mudstone shale, with slim layers of sandstone and limestone. Coloring ranges from green, grey, to brownish tan.
Tapeats Sandstone – Approximately 545 million years. Formed of different grained sandstones. Dark brown colored.
An unconformity is found here. Layers previously here have been eroded away.
Vishnu Schist – Approximately 1,700 to 2,000 million years old. Made of Mica Schist. “Originally sediments of sandstone, limestone and shale that were metamorphosed and combined with metamorphosed lava flows to form the schist.” (Paraphrased and quoted from Bob Ribokas). http://www.bobspixels.com/kaibab.org/geology/gc_layer.htm
By positioning a chart of these layers next to a chart of the GTS
and one can see how the dating of these layers is evidence for the factualism of
the Geologic Time Scale
Although there are no layers present revealing the Ordovician or the Silurian periods, any layers which would be present now have been eroded away before the beginning of the . As shown by this chart, the layers of rock found in the Grand Canyon match together according to the Geologic Time Scale.
Works Cited
http://www.bobspixels.com/kaibab.org/geology/gc_layer.htm
http://www.bobspixels.com/kaibab.org/geology/gc_geol.htm
http://www.geo-images.com/twds2.jpg
