Chapter 8: Geologic Time & the Grand Canyon

Geologic TimeGrand Canyon National Park

Colorado Plateau • nearly-horizontal _______________________ rocks

lifted ________________________ feet above sea level

• _____________ River drains ___________ Mtns Who was John Wesley Powell?

Label the Glen Canyon Dam. Where is the mouth of the Colorado River? The Grand Canyon is _____________ miles long; _______ feet deep; and _______ miles at its widest point.

Explain the pattern in the stream flow graph. What was the 2008 High Flow Experiment? The canyon’s north rim (8900’) averages 1200’ higher than the south rim. Explain why.

Which formation composes the rim of the Grand Canyon? What layers were originally above that formation? What happened to them at the Grand Canyon? Where can you see them now?

How does a slot canyon form? In what layer are springs common? Why?

What types of rocks form the Inner Gorge? What is their origin?

What is the difference between "relative" dating and "absolute" dating?

What is an unconformity? Draw a sketch of an angular unconformity. Use Fig. 8.8 to explain the sequence of events that produces an angular unconformity.

What is a nonconformity? Draw a sketch. Use Fig. 8.6 to explain the sequence of events that produces a nonconformity.

Which is older (circle):

• A or B Principle used: ____________________________

• D or F Principle used:_____________________________

• D or E Principle used: ____________________________

• G of E Principle used: ____________________________

Fig. 8.9 What is the feature labeled F? What type of rock is it? What is the feature labeled D? How is it different from feature F? What are inclusions?

What job did "Strata" Smith have?

Types of fossils: Fig. ________ What is a trace fossil? What is petrified wood made from? What is amber? What is a coprolite?

Any time period can be recognized by its __________________________________________.

– “Paleozoic” __________________ life

– “Mesozoic” __________________ life

– “Cenozoic” __________________ life

The Phanerozoic represents only ____% of Earth's history. What is the significance of the K-T Boundary? K = ________________________ T= _________________________ What is "correlation?" (Fig. 8.13)

Radioactivity: ____________________________ of atomic nuclei.

“__________________” elements decay to

“___________________________________”

What happens to the atomic number and mass after alpha emission? What happens to the atomic number and mass after beta emission? What happens to the atomic number and mass after electron capture?

• Rate of decay is unaffected by ____________________ and _____________

• Metamorphism (recrystallization) “_________________________________ ” ; if you use radioactive decay to date a metamorphic rock, you determine:

• ____________________ igneous rocks best What elements are often used to date rocks? Why is carbon NOT useful in dating rocks?

Problem: Element R decays to element S. The half-life of R is 5 years. If you have 600g of R now, how much will you have in 20 years?

Stratigraphic Section of Grand Canyon Rocks

The unconformity represents _____________ years before younger Precambrian sedimentary rocks were deposited. On the stratigraphic section above, draw a line to highlight the unconformity represented by the yellow dashed line in the diagram at left.

What is the Grand Canyon Supergroup? How thick is it?_______________________ feet What color are they on the stratigraphic section? What are stromatolites? What rocks are on top of the Grand Canyon Supergroup? What type of contact is it?

Top: ___________________ formed block-faulted mountain ranges. Supergroup rocks were preserved in basins between mountain uplifts. Bottom: A long period of _______________ followed. A broad, gently rolling landscape was carved on the Precambrian rocks.

What environmental conditions are represented by the Coconino Sandstone? What evidence does the rock layer contain? What environmental conditions are represented by the Kaibab Limestone? What evidence does the rock layer contain?

Carving the Canyon— When the Gulf of California opened ___________ Ma, the sudden change in _______________________ from the plateau’s surface to sea level, several thousands of feet lower, initiated rapid _____________________by the Colorado River and the formation of the Grand Canyon.

What is Vulcan’s Throne? When did it form?

Chapter 8 Study Guide Important Dead Guys: John Wesley Powell, James Hutton, William “Strata” Smith Describe how the principles of relative dating can be used to unravel the sequence of geologic events in a

region. Describe the sequence of events that produce an angular unconformity. Contrast that with a

nonconformity. Describe the basic principles used to construct the geologic time scale. List in order the main subdivisions (eras) of the Phanerozoic. Name a major type of organism each era is

known for. Explain the significance of the K-T boundary. Describe how fossil assemblages can be used to trace rock layers or time units over large areas. Describe the different types of radioactive decay and the changes they produce in the daughter products. Explain how the half-life of an isotope can be used to determine the age of a sample. Name the elements that are typically used in radioactive dating of rocks. List some limitations of radioactive dating. Based on the stratigraphic section of rocks at the Grand Canyon, outline the general sequence of events

that have produced the rocks. Include the names of some of the most distinctive rock units. What types of environments are represented by major rock units in the Grand Canyon? What kinds of

evidence do they hold? What event initiated the downcutting of the Colorado River in the Colorado Plateau? What is the most recent rock in the Grand Canyon area? Vocabulary: Relative Dating Superposition Original horizontality Cross-cutting features Fault Fold Unconformity Dike Sill Angular unconformity Nonconformity Principle of faunal succession Correlation Inclusions

Fossil Paleontology Fossil assemblage Trace fossil Petrified wood Amber Coprolite Mold and cast Phanerozoic Paleozoic Mesozoic Cenozoic K-T boundary Mass extinction

Absolute age Radioactivity Parent isotope Daughter product Alpha emission Beta emission Electron capture Half life Vishnu Basement Grand Canyon Supergroup Stromatolites Redwall Limestone Coconino Sandstone Kaibab Limestone Vulcan’s Throne

Earth Revealed Video Programs: ER # 10: Geologic Time ER # 11: Evolution Through Time