Geology Chapters 9 and 10 Reading Homework

Match the words in the left column to the appropriate blanks in the sentences on the right. Note that some terms will remain unused and some may be used more than once.

1. During electron capture, the mass number remains unchanged. 2. In electron capture, when an electron and a proton combine to form an additional neutron, the nucleus will now contain one less proton. This affects the atomic number by a decrease of -1. 3. In beta particle emission, the nucleus will end up containing one more proton. 4. If 1:7 is the ratio of radioactive parent atoms to stable daughter atoms, there is one parent for every 7 daughter atoms, and 3 half-lives have passed.

Complete the following sentences regarding deformations resulting from stress. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer. You do not need to use all terms.

1. Large rifts or valleys, which can often have very large normal faults, are created by tensional forces. 2. If a rock undergoes folding and is compressed to form an upward arch, this is a(n) anticline type fold. 3. A trough, or downward fold, called a(n) syncline is formed when a rock is deformed through folding. 4. 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 joint. If, however, there is movement, it is called a fault.

What is the half-life of potassium-40?

1.3 billion years

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

An isotope sample initially weighing 500 grams decays to produce a daughter element. What is the amount of parent element remaining after two half-lives?

125 grams

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

Chemical analysis on a rock specimen has shown a ratio of 1:3 for radioactive parent to stable daughter product. If the radioactive isotope in this rock has a half-life of 10,000 years, how old is this rock?

20,000 years

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

What remains after a sample undergoes two half-lives?

25 percent of the sample is composed of parent atoms, and 75 percent of the sample is composed of daughter atoms.

If one half-life has lapsed, what is the radioactive parent to stable daughter isotope ratio?

50:50

You are trying to determine the age of a lava flow using an isotope with a half-life of 1.5 million years. If the sample has gone through four half-lives, what is the age of the rock?

6 million years

What is a fault?

A fracture in a rock along which motion has occurred

What is the definition of an inclusion?

A fragment of one rock unit enclosed in another rock unit

What is the difference between a reverse fault and a thrust fault?

A thrust fault has a fault angle of less than 45°, whereas the angle of a reverse fault is greater.

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.

Based on the same principles as above, classify the radioactive decays as alpha emission, beta emission, or electron capture. Drag the appropriate items into their respective bins. Each item may be used only once.

Alpha emission 226Ra88226Ra88 decays to 222Rn86222Rn86 218Po84218Po84 decays to 214Pb82 Beta emission 234Th90234Th90 decays to 234Pa91234Pa91 40K1940K19 decays to 40Ca20 Electron capture 40K1940K19 decays to 40Ar18

What is an isotope?

An atom that has more or fewer neutrons than it should

What is the significance of an unconformity?

An unconformity represents an interval of time that is missing from the rock record.

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

Angular unconformities separate rock layers along nonparallel surfaces.

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

Arrows moving opposite directions, north and south nothing on land

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. Select the three that apply.

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.

Examine the radioactive isotope of thorium in the accompanying illustration. Note its atomic number and mass number. If six alpha particles and four beta particles are emitted during radioactive decay, what will the daughter product's atomic number and mass number be? Drag the appropriate labels to their respective targets.

Atomic number:82 Mass Number:208

Imagine two rocks. Under enough stress, rock A will experience plastic strain, whereas rock B will experience brittle strain. Which of the following statements about rocks A and B is true?

Both rock A and rock B will experience elastic strain before plastic or brittle strain sets in.

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.

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. Drag the appropriate items to their respective bins. Each item may be used only once.

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

Which era are we currently in?

Cenozoic

What kind of stress is deforming this block? Arrows pointed inward

Compression

Which tectonic boundary is associated with compressional stress?

Convergent

Which tectonic boundary would likely have many thrust faults associated with it?

Convergent

In the images below, which contains a disconformity?

Dark pink sedimentary rock 3 Beige sedimentary rock 2 squiggly line Light pink sedimentary rock 1

________ refers to the changes in shape or position of a rock body in response to differential stress.

Deformation

What kind of unconformity is visible in this figure? The unconformity in the question is indicated by the Arrow B.

Disconformity

What scientific development made accurate numerical dating possible?

Discovery of radioactivity

Which tectonic boundary would have many normal faults associated with it?

Divergent

The Mississippi River cuts through Silurian-aged dolomite between northwestern Illinois and eastern Iowa. Which is older? How do you know?

Dolomite; the principle of cross-cutting relationships

You are accuracy-checking a geologic map of a structural dome with the inner layers dating back to the Tertiary and its outer layers dating back to the Permian. You immediately know this map is wrong. What is your evidence?

Domes have the oldest layers in the middle, not the youngest.

Unbending a paper clip wire is an example of what kind of deformation?

Ductile deformation

A rubber band being stretched in preparation to fire across the room is an example of what kind of deformation?

Elastic deformation

Which of the following statements is true about erosion?

Erosion varies from place to place.

All isotopes are unstable.

False

Shear stress is a type of confining pressure.

False

The oldest rocks on Earth date back to 4.28 billion years old and were found in western Australia.

False

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.

What is the principle of cross-cutting relationships?

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

What is the orientation of a fold's hinge line with respect to the orientation of plunge?

Hinge line is in the direction of plunge.

Which of the following represents the shortest division of time?

Holocene

What is the difference between faults and joints?

Joints form in place, whereas faults form because rock has moved.

Which of the following statements regarding radioactive decay is true?

More daughter products accumulate over time.

What kind of unconformity is visible in this figure? The unconformity in question is indicated by the Arrow A.

Nonconformity

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.

Match the fault with the appropriate stress that caused it. Drag the terms on the left to the appropriate blanks on the right.

Normal fault −− Tension Reverse fault −− Compression Strike-slip fault −− Shear

__________ faults combine elements of strike-slip and dip-slip motions.

Oblique-slip

Which of the following best describes the age relationship of the layers in a syncline?

Oldest on the outside of the fold, youngest on the inside

What materials are best dated with carbon-14?

Organic materials

What kind of fold is visible in this figure? oval figures with line going threw it

Overturned fold

What happens during radioactive decay?

Parent isotopes turn into daughter isotopes.

Primates have existed for approximately 1.3 percent of geologic time. The Phanerozoic eon, the present Eon, is 10.84 percent of geologic time. Life has existed on Earth approximately 76 percent of geologic time. Label the accompanying geologic time scale for when these historical events began. The labels that you will place on the scale include events in Earth's history and number of years (in millions of years) before present. Round the age of Earth to 5 billion years. Note that the years indicated are millions of years ago. For example, the most recent age on the chart is 65.5 million (65,500,000) years ago. Drag the appropriate labels to their respective targets. You do not need to use all labels.

Phanerozoic- first primates appear precambrain -life starts 542

________ is a term used to define 88% of Earth's history prior to the start of the Paleozoic era.

Precambrian

What is the definition of relative dating?

Putting events in order from first to last

________ is a technique where the decay rate of radioactive isotopes is measured and used to determine the age of a geologic material.

Radiometric Dating

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.

What is the principle of original horizontality?

Sedimentary rocks are close to horizontal when deposited.

What kind of stress is deforming this block? Arrows pointed opposite sides

Shear

How does compressional force change a rock body?

Shorten and thicken the rock

How does tensional force change a rock body?

Stretch and thin the rock

Match the relative dating principles with the correct definition. Drag the terms on the left to the appropriate blanks on the right.

Superposition− the oldest is on the bottom, the youngest on top. Original horizontality− sedimentary layers/lava are deposited in horizontal layers. Lateral Continuity− rocks extend in all directions until they reach the edge of a basin or pinch out. Cross-Cutting Relationships− faults, fractures are younger than the rocks they cut through. Unconformities− missing time. Inclusions− chunks of weathered rock are older than the rock they are contained in.

What kind of stress is deforming this block? Arrows pointed outward

Tension

Determine whether each geologic feature is being caused by tensional, compressional, or shear stresses by analyzing the directions of the forces being applied. Drag the appropriate items to their respective bins. Each item may be used only once.

Tensional: Normal fault Compressional: Folded rock, reverse fault, and thrust fault Shear: Strike-slip fault

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.

What is the outcrop pattern of a plunging syncline?

The layers will open up in the direction of plunge.

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 happens when stress exceeds a plastic rock's yield strength?

The rock will experience flow.

What happens when stress exceeds a brittle rock's yield strength?

The rock will experience fracture.

What is the definition of a half-life?

The time it takes for half of the parent isotope to decay to the daughter

Imagine two rocks. Rock A is weaker than rock B. Which of the following statements about rocks A and B is true?

The yield strength of rock A is lower than that of rock B.

How will the orientation of a plunging anticline's limbs change in the direction the fold is plunging?

They will close to a point.

Which image is an example of an angular unconformity? SEE IMAGES BELOW FOR ANSWER SELECTIONS.

Triangular image

An anticline is an upfold in rock where the oldest layers are in the middle of the fold and the youngest are on the outside.

True

Radioactive decay in mineral shows that two half-lives have elapsed, giving an age of approximately 1.4 billion years. Using the table in the video as a reference, what is the correct radioactive parent and stable daughter isotope pair?

U235, Pb207

Match the parent isotope with the correct daughter isotope. Drag the terms on the left to the appropriate blanks on the right. (Terms can be used once, more than once, or not at all.)

Uranium −− Lead Potassium−− Argon Carbon −− Nitrogen Thorium −− Lead Rubidium −− Strontium

Where do valleys tend to form in a landscape?

Valleys form where rock layers are easily erodible (soft).

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

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 includes all common types of radioactive decay?

alpha particle emission, beta particle emission, electron capture

Which type of fold has rocks folding up in the middle?

anticline

What kind of force would create the fault in Figure 1?

compression

Which type of force causes folding? inward arrows

compressional force

Which type of force is responsible for reverse fault formation?

compressional force

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) ________ is a type of unconformity with parallel beds above and below the erosional surface.

disconformity

Which type of rock is best suited for radiometric dating?

granite

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

What is the hinge line of a fold?

line of maximum inflection that layers wrap around

Horizontal cretaceous limestone directly overlying horizontal Cambrian granite is an example of a(n) ____.

nonconformity

What kind of fold is circled in Figure 1?

nonplunging syncline

A ________ fault is created when the hanging wall moves down relative to the footwall.

normal

Which fault will see the hanging wall move down relative to the footwall?

normal fault

Which fold orientation is visible in Figure 2?

overturned

In radioactive decay, an unstable ________ isotope will decay into a stable ________ isotope.

parent; daughter

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

Two isotopes of uranium, 238U and 235U, have the same number of ___, but different numbers of ___.

protons; neutrons

The same type of stress that creates anticlines and syncline in some rocks will create ____ faults in rocks that exhibit brittle deformation.

reverse and thrust

What kind of fault is visible in Figure 1?

reverse fault

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

reverse faulting folding

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

shear force

A chocolate bar will behave similarly to a rock. If you try to bend a chocolate bar at room temperature it will ________ exhibiting ________ behavior.

snap; brittle

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

strike-slip fault

Which of the following terms best describes the orientation of the fold in Figure 1? land divided in half, both sides look identical

symmetrical

Which kind of fold is visible in Figure 3?

syncline

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

tension

Which type of force is responsible for normal fault formation?

tensional force

What is strain?

the amount of deformation that results from an applied force

What is the scientific definition of half-life?

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

What are rocks below and above a fault called?

the footwall below and the hanging wall above

What is stress?

the force exerted to cause deformation

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