Chapters 9 and 10

Which of the following scenarios best describes the deformation that will occur in different parts of the crust?

Brittle deformation is dominant in the shallow crust; ductile deformation is dominant in the deep crust.

Using the principle of inclusions, rank the labeled areas from oldest to youngest.

CABD

What is the principle of cross-cutting relationships?

Geologic features that cut through rocks must form after the rocks that they cut through.

What happens during radioactive decay?

Parent isotopes turn into daughter isotopes.

Which of the following statements about relative and absolute age dating is most accurate?

Relative age dating places rocks and events in chronological order but does not provide information about absolute age.

Imagine a syncline has been eroded to a flat surface. How would the rock age change as you walked across that flat surface?

Rocks would be oldest on the edges and youngest in the middle.

Imagine an anticline has been eroded to a flat surface. How would the rock age change as you walked across that flat surface?

Rocks would be youngest on the edges and oldest in the middle.

An igneous dike cuts across existing sedimentary layers and erupts at the surface, creating a layer of basalt. The basalt, as well as all the layers below, are then cut by a fault. Which statement is true?

The fault is the youngest because it cuts through all the sedimentary layers and basalt.

the principle of superposition

While visiting the Grand Canyon, you are amazed by the depth of layers of sedimentary rock before you - the principle of superposition is evident here where progressively younger layers have formed over time and are stacked upon each other.

What is the principle of superposition?

Within a sequence of rock layers formed at Earth's surface, rock layers lower in the sequence are older.

What produces plunging folds?

a combination of folding and tilting

What is a syncline?

a fold shaped like a right-side-up U

What is an anticline?

a fold shaped like an upside-down U

Which of the following is a common feature that all unconformities exhibit?

erosive surface

A sandstone contains inclusions of metamorphic rock. An igneous dike cuts both the sandstone and inclusions. List the rocks from youngest to oldest.

igneous dike, sandstone, metamorphic rock

When a rock is under undue stress and fractures but there is no movement to either side of the fracture, the feature is a called a ___ . If, however, there is movement, it is called a ___ .

joint fault

In the following rock sequence, how much erosion might have occurred between rock layer A and rock layer B? (Rock Layer B is above A)

none or only a very small amount (Time does not equate to erosion.)

An undeformed sequence of sedimentary rocks is exposed in a large river canyon. Which two principles would be demonstrated by the rocks?

principles of superposition and lateral continuity

Which of the following is an example of how rocks will respond to compressional stress? (Note: there may be more than one correct answer.)

reverse faulting folding

Which type of force is responsible for normal strike-slip formation?

shear

A _____ is formed when magma intrudes between existing sedimentary layers.

sill

A trough, or downward fold, called a(n) ___ is formed when a rock is deformed through folding.

syncline

Which tectonic stress will result in a lengthening of the crust?

tension

What scenario requires a geologist to use the principle of cross-cutting relationships?

A dike truncates layers in a sedimentary succession.

older

A fault cuts through layers of limestone, sandstone, and conglomerate. The surrounding layers must be older than the fault.

younger

A mass of granite has inclusions of surrounding sandstone. The sandstone and surrounding layers show evidence of uplift over time. The granite must be younger than the sand deposits.

If a sequence of sedimentary units is cut by a fault, what does the principle of cross-cutting relationships tell a geologist?

All of the sedimentary units must have been deposited and lithified before being cut by the fault.

What characteristic most directly DISTINGUISHES an angular unconformity from a nonconformity?

Angular unconformities separate rock layers along nonparallel surfaces.

the principle of original horizontality

Applying the principle of original horizontality indicates that layers were repositioned from a flat-lying orientation.

Which of the following images best describes how a rock in the deep crust would be deformed as a result of shear stress?

Arrows going up and down without breaking the crust

Percents help us understand how the parts of something, like a pizza slice or a natural event, relate to the entirety of the pie or Earth's history. Calculate the length of time of the following events as a percent of Earth's age. Round the age of Earth to 5 billion years old.

Assume the length of recorded history is 5,000 years. It is correct to say recorded history represents 0.0001 percent of geologic time. If human-like ancestors have been around approximately 5 million years, it is correct to say this represents 0.1 percent of geologic time. Evidence of abundant fossils date back to 540 million years ago. It is correct to say this represents 10.8 percent of geologic time.

John is assisting a geologist who has traveled across the world and collected a few samples. He asks John to classify the samples that can be dated using carbon-14 and uranium-235 (or U-235). All organic materials contain carbon and are dated using C-14; inorganic materials are dated using any radioactive element, such as uranium, rubidium, potassium, and thorium, except carbon. Now, help John group the samples.

Carbon-14 dating: Egyptian mummies wood piece U-235 dating: granite gneisses volcano ash

Five layers of rock are cut by two faults. Both faults cut through all five layers of rock. Fault A breaks through to the surface, whereas fault B does not. Which of the following statements about faults A and B is most accurate?

Fault A is younger than fault B, and both are younger than the five layers of rock.

An igneous dike cuts through limestone, but not through the overlying sandstone. Which of the following statements is most accurate?

First, the limestone was laid down, then intruded by the igneous dike, and lastly the sandstone was deposited.

Which of the following describes the principle of original horizontality?

Folded sedimentary layers were originally laid down flat and later deformed.

the principle of crosscutting relationships.

Magma intrudes into layers of sedimentary rock and displaces them. We can deduce that the intruded magma that crystallizes is younger than the surrounding sedimentary layers by applying the principle of crosscutting relationships.

Imagine a fold has been eroded to a flat surface. In general, how would you know whether this fold is plunging?

Nonplunging folds look like straight lines at the surface, and plunging folds look like wavy lines.

What is the principle of original horizontality?

Sedimentary rocks are close to horizontal when deposited.

A fault (F) breaks three layers of sedimentary rock (S). An igneous intrusion (I1) has broken through the bottommost layer of rock. A second igneous intrusion (I2) has moved up the fault and pooled on top of the uppermost layer of rock. Which event would be considered the youngest?

The intrusion of I1 or I2 is the youngest event. Without more information, we cannot know which igneous rock is youngest.

If a limestone, a shale, and a sandstone are deposited in that order without interruption, which of the following is true?

The limestone is the oldest and the succession is conformable.

Two containers hold the same radioactive isotope. Container A contains 1000 atoms, and container B contains 500 atoms. Which of the following statements about containers A and B is true?

The rate of decay of atoms (half-life) in container B is the same as the rate of decay of atoms (half-life) in container A.

What does the term plunging fold mean?

a fold that is tilted down into Earth

What does the term unconformity mean?

a missing rock layer in a sequence that represents a period of erosion or nondeposition

Which of the following is associated with an erosive surface?

a stream running across an irregular surface

If a rock undergoes folding and is compressed to form an upward arch, this is a(n) ___ type fold.

anticline

Which type of force causes folding?

compressional force

Which type of force is responsible for reverse fault formation?

compressional force

Following the deposition of a sequence of sedimentary rocks, which event is the first to occur to produce an angular unconformity?

deformation

Which list best describes the events that would lead to the layering of sedimentary rocks in this diagram?

deposition, erosion, deposition, erosion, deposition

A(n) __________ exhibits sedimentary layers that are parallel to each other above and below an erosive surface.

disconformity

What is a fault?

fractures along which rocks move

Large rifts or valleys, which can often have very large ___ faults, are created by tensional forces.

normal

Which type of fault has NO vertical motion of rocks associated with it?

stike-slip

Which type of force is responsible for normal fault formation?

tensional force

What is the scientific definition of half-life?

the amount of time over which the number of parent isotopes decreases by half

In the images below, which contains a disconformity?

the bottom layer isnt flat

What are rocks below and above a fault called?

the footwall below and the hanging wall above

Which image is an example of an angular unconformity?

the one on an angle

Which principle of relative age dating is important for determining the relative age of igneous rock that has intruded into overlying rock?

the principle of cross-cutting relationships

The sedimentary layers above an erosive surface are __________ relative to all rocks present below the surface.

younger

Which of the following is an accurate description of a nonconformity?

younger sedimentary strata overlie uplifted and weathered igneous or metamorphic rocks

A container holds 100 atoms of an isotope. This isotope has a half-life of 1.5 months. How many total atoms will be in the container after 3 months?

100 atoms

You attend a geology lab where you are asked to estimate the age of a fossil. The ratio of parent to daughter elements in the fossil sample is 1:7. You know that fossils are the remains of living organisms, which have some amount of C-14 isotope. The C-14 isotope, which has a half-life of 5730 years, begins to decay as the organism dies. What would be your estimation of the fossil's age?

17,190

A container holds 100 atoms of an isotope. This isotope has a half-life of 1.5 months. How many atoms of the radioactive isotope will be in the container after 3 months?

25 atoms