GEOL 101 Chapter 15

A container hold 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

After four half-lives of decay, what is the ratio of radioactive parent isotope to stable daughter isotope?

1:15

Which of the following is associated with an erosive surface?

A stream running across an irregular surface.

How is the atomic number of an atom determined?

Counting the number of protons in the nucleus.

What is the principle of cross-cutting relationships?

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

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

Which of the following characteristics is the most desirable for constraining the relative age of rocks

Organisms with overlapping ranges and geologically short lifespans.

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

Original horizontality

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

Paleozoic, Mesozoic, Cenozoic

What happens during radioactive decay?

Parent isotopes turn into daughter isotopes.

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

Phanerozoic

Which material, principle, or process enables a method of numerical dating?

Radioactivity

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

Scallop

A radioactive element undergoes decay via the loss of two alpha particles to form a stable daughter isotope. Following the decay, what would the atomic number of this newly created stable isotope be?

The atomic number of the daughter isotope would be four units less than the original parent isotope.

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.

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 and I2 is the youngest event. without more information, we cannot know which igneous rock is youngest.

What is the best definition of fossil range?

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

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.

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

Widespread occurrence of hard parts.

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.

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

sill

In the images below, which contains a disconformity?

the one that has the jagged line in between sedimentary rock 2 and 1

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

the only triangular looking one

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.

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

Deposition, erosion, deposition, erosion, deposition

Which is an example of radioactivity that occurs when a neutron is converted to a proton and an electron is emitted from the nucleus?

Emission of a beta particle

Which is the shortest interval of geologic time?

Epoch

An ingeous 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.

What is the principle of original horizontality?

Sedimentary rocks are close to horizontal when deposited.

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

Superposition

What is the scientific definition of half-life?

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

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.

If a rock contains ten different kinds of fossils, which of the following must be true?

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

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

Nonconformity

Which process is not a common form of natural radioactive decay?

Nuclear fission

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.

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.

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

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

Types of fossils within the units.

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

A dike truncates layers in a sedimentary succession.

What does the term unconformity mean?

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

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.

Which of the following describes the principle of original horizontality?

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

In the following rock sequence, how much erosion might have occurred between rock layer A and rock layer B?

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.

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

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 applying which law or principle?

The principle of cross-cutting relationships.

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