GEO: HW 9

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 is the principle of cross-cutting relationships?

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

Which represents the correct sequence from oldest to most recent or current eras on the Geologic Time Scale?

Paleozoic, Mesozoic, Cenozoic

Part complete Which eon translates to "visible life" from the Greek?

Phanerozoic

What is the principle of original horizontality?

Sedimentary rocks are close to horizontal when deposited.

At the road cut, which rocks are the LEAST resistant to weathering and erosion, and where are these rocks located?

Shales and mudstones to the west

How is the geologic time scale related to the fossil record?

The periods of the time scale were constructed based on ranges of fossil organisms.

Over what span of time were the tracks most likely created?

Weeks

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.

Which organism from the video is the least useful for relative dating?

scallop

Which principle or law of geology states that in a sequence of undeformed sedimentary rocks, each bed is older than the one above?

superposition

The subdivisions of the Geologic Time Scale were based on which criteria or characteristics?

types of fossils within the units

Which event is generally used to indicate the beginning of the Phanerozoic eon?

widespread occurrence of hard parts

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

younger

What is the best definition of fossil range?

The period of time when an organism first and last appears in the sedimentary record.

If a rock contains ten different kinds of fossils, which of the following must be true? a. All of the organisms had to be alive when the rock was deposited. b. All ten organisms went extinct at the same time. c. All of the fossils are useful in constraining relative age. d. These organisms give the minimum age of the rock. e. All ten organisms evolved at the same time

a. All of the organisms had to be alive when the rock was deposited.

Which answer most correctly describes the relative ages of the rock units visible in the placemark A pop-up balloon? a. The shales and mudstones to the west are older than the shales and sandstones to the east. b. The shales and mudstones to the east are older than the shales and sandstones to the west. c. The shales and mudstones to the east are younger than the shales and sandstones to the west. d. The shales and mudstones to the west are younger than the shales and sandstones to the east.

a. The shales and mudstones to the west are older than the shales and sandstones to the east.

Which of the following characteristics is the most desirable for constraining the relative age of rocks? a. organisms that do not overlap in range b. organisms with overlapping ranges and geologically short lifespans c. organisms that are soft-bodied and microscopic in size d.organisms that overlap in range and are geologically long-lived d. organisms that span long periods of geologic time

b. organisms with overlapping ranges and geologically short lifespans

In order for the ripple marks shown in the image to have been preserved and exposed at the surface, a unique series of events must have taken place. Which of the following answers most accurately describes this series of events? a. Wave action in deep water overlying soft, sandy sediments produced ripple marks in the sediments. Deposition of more and more sediment buried these sediments to depths great enough for lithification to occur. Later, the sedimentary rock containing these preserved ripples were uplifted, tilted to the east, and ultimately re-exposed at the surface by weathering and erosion (here helped by a road-building crew). b. Wave action in shallow water overlying soft, sandy sediments produced ripple marks in the sediments. Growth of blue-green algae mats cemented the ripples in place before the next tide could destroy them. Lithification occurred as the blue-green algae secreted their silica gel and cemented the grains in place. When the next tide came in, the algal mat absorbed iron from the water, which further cemented the ripples in place. Later, the sedimentary rock containing these preserved ripples was uplifted, tilted to the east, and ultimately re-exposed at the surface by weathering and erosion (here helped by a road-building crew). c. Unidirectional current in shallow water overlying soft, sandy sediments produced ripple marks in the sediments. Deposition of more and more sediment buried these sediments to depths great enough for lithification to occur. Later, the sedimentary rock containing these preserved ripples was uplifted, tilted to the east, and ultimately re-exposed at the surface by weathering and erosion (here helped by a road-building crew). d. Wave action in shallow water overlying very coarse, sandy sediments produced ripple marks in the sediments. Deposition of more and more sediment buried these sediments to depths great enough for lithification to occur. Later, the sedimentary rock containing these preserved ripples was uplifted, tilted to the east, and ultimately re-exposed at the surface by weathering and erosion (here helped by a road-building crew).

b. Wave action in shallow water overlying soft, sandy sediments produced ripple marks in the sediments. Growth of blue-green algae mats cemented the ripples in place before the next tide could destroy them. Lithification occurred as the blue-green algae secreted their silica gel and cemented the grains in place. When the next tide came in, the algal mat absorbed iron from the water, which further cemented the ripples in place. Later, the sedimentary rock containing these preserved ripples was uplifted, tilted to the east, and ultimately re-exposed at the surface by weathering and erosion (here helped by a road-building crew).

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? a. The rate of decay of atoms in container B is the same as the rate of decay of atoms in container A. b. The rate of decay of atoms in container B is greater than the rate of decay of atoms in container A. c. The rate of decay of atoms in container A is greater than the rate of decay of atoms in container B.

c. The rate of decay of atoms in container A is greater than the rate of decay of atoms in container B.

Which is the shortest interval of geologic time?

epoch

While working in the field, you find some sedimentary rocks that include hundreds of fossils of crinoids, numerous brachiopods, and a few trilobites. Realizing that these ancient organisms are some of the first with hard parts, and (when taken as a group) are not very similar to animal communities living today, in which unit of geologic time would you place these rocks?

the Paleozoic

What is the scientific definition of half-life?

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

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

While working in the field, you encounter an outcrop in which sandstone, shale, and limestone have been intruded by a basaltic dike. You know that the basaltic dike is younger than the sedimentary rock by applying which law or principle?

the principle of cross-cutting relationships

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

50:50

The rocks steeply dip eastward, which suggests that these rocks have been uplifted and deformed. What law of relative dating could be used to establish this observation?

Law of original horizontality

What law of stratigraphy did we apply to determine the relative ages of the rocks here?

Law of superposition: in most sedimentary sequences, the oldest rocks are on the bottom.

What happens during radioactive decay?

Parent isotopes turn into daughter isotopes.

In the field you encounter a sequence of sedimentary rocks that has a dike running through them. A normal fault crosses the entire sequence, cutting off part of the dike near the surface. Which scenario best describes your observations? (All scenarios list events from oldest to youngest.)

The relative ages of the sequence are as follows: sedimentary rocks > dike > normal fault.

Which of the following includes all common types of radioactive decay? a. alpha particle emission, beta particle emission, electron capture b. alpha particle emission, beta particle emission, radioactive parent isotope c. alpha particle emission, stable daughter, electron capture d. alpha particle emission, beta particle emission, half-life e. atomic number, beta particle emission, electron capture

a. alpha particle emission, beta particle emission, electron capture

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? a. Faults A and B are about the same age, and both are younger than the five layers of rock. b. Fault A is younger than fault B, and both are younger than the five layers of rock. c. Faults A and B are about the same age, and both are older than the five layers of rock. d. Fault A is younger than fault B, and both are older than the five layers of rock.

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

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? a. The intrusion of I2 is the youngest event. We can know this because I2 sits on top of all other rocks. b. The intrusion of I1 or I2 is the youngest event. Without more information, we cannot know which igneous rock is youngest. c. Faulting of rock along F is the youngest event. We know this because all three layers of sedimentary rock have been broken. d. Deposition of the three sedimentary layers, S, is the youngest event. We know this because the fault underlies the igneous rocks.

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

Which of the following statements about relative and absolute age dating is most accurate? a. Relative age dating provides information about absolute ages but does not place rocks and events in chronological order. b. Relative age dating places rocks and events in chronological order and can provide information about absolute age. c. Relative age dating does not provide information about absolute ages, nor does it place rocks and events in chronological order. d. Relative age dating places rocks and events in chronological order but does not provide information about absolute age.

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

Scientists have suggested that the downward bulges in the Jurassic sandstone layers along Dinosaur Ridge are the "mudholes" created when a dinosaur or two walked in mud and squeezed the layers together. In order for the deep bulges shown in the image to have been created, a unique series of events must have taken place. Which of the following must NOT have been part of this series of events? a. Soft, muddy sediments were deposited, perhaps in a swampy environment. A "bronto" walked across the sediments, leaving deep footprints in the mud. b. The sedimentary rock was uplifted and tilted to the east. Years of weathering and erosion eventually exposed the footprints in cross section on the flanks of the Dakota Hogback. c. Mud and other sediments filled in the footprints. The sediments were eventually lithified into sedimentary rock. d. The footprints remained exposed at the surface for many years.

d. The footprints remained exposed at the surface for many years.

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

deformation

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

disconformity

Which of the following statements regarding radioactive decay is true? a. A mineral starts out with a parent:daughter isotope ratio of 75:25. b. The number of half-lives decreases over time. c. More parent isotopes accumulate over time. d. The nucleus of a radioactive particle is not affected. e. More daughter products accumulate over time.

e. More daughter products accumulate over time.

Which of the following is an accurate description of a nonconformity? a. horizontal sedimentary rocks that have been laid down without interruption b. younger, relatively flat-lying sedimentary rocks overlie older, tilted sedimentary rocks c. younger horizontal sedimentary rocks overlie an erosive surface, with older parallel sedimentary rocks present below d. an igneous intrusion that causes sedimentary layers to uplift and erode e. younger sedimentary strata overlie uplifted and weathered igneous or metamorphic rocks

e. younger sedimentary strata overlie uplifted and weathered igneous or metamorphic rocks Submit

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

erosive surface

What term describes an erosional surface bounded above by flat-lying sedimentary rocks and below by igneous or metamorphic rocks?

nonconformity

The fact that sedimentary rocks are almost always deposited in a horizontal position reflects which law or principle of geology?

original horizontality

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