DATE DUE:                                                                               NAME:                                                             
INSTRUCTOR: TERRY J. BOROUGHS
Geology 305                                                                             SECTION:                                                        

 

GEOLOGICAL TIME / DATING TECHNIQUES

Instructions:     Read each question carefully before selecting the BEST answer. Provide specific and detailed answers to essay questions. Use GEOLOGIC VOCABULARY where APPLICABLE! USE AN 882 SCANTRON TO RECORD YOUR ANSWERS FOR THE FOLLOWING MULTIPLE CHOICE AND T/F QUESTIONS.  TURN IN YOUR SCANTRON AND ANSWER SHEET ONLY!  

True = A / False = B

1.              A Half life is the number of atoms that decay per unit of time.

2.              Radiometric dating means placing events in their proper sequence.

3.              After four half-lives there is no longer any of the original radioactive material remaining.

4.              Inclusions are pieces of one rock contained within another.

5.              The radioactive isotope, potassium-40, has Argon-40 as a daughter product.

6.              The percentage of radioactive atoms that decay during one half-life will change.

7.              An unconformity involving older metamorphic rocks and younger sedimentary strata is termed an disconformity.

8.              In reference to the geologic time scale, periods are divided into smaller time units called epochs.

9.              It is usually not possible to obtain an accurate radiometric date from a sample of detrital sedimentary rock.

10.           Coal swamps are associated with the Pennsylvanian period.

11.           The geologic time scale was originally constructed by scientists with the aid of numerical dates, because radioactivity had already been discovered.

12.           We are now living in the Cenozoic era.

13.          James Hutton's principle of uniformity states that "the past is the key to the present."

14.          Probably the single most characteristic feature of the Phanerozoic is its great abundance of fossil evidence.

15.           The law of superposition is used in relative dating.

16.          In regards to cross-cutting relationships, if rock B cross-cuts rock A, then A is younger than B.

17.          Any interval of geologic time not represented by strata in a particular area is a hiatus.

18.          Key/index/marker beds are particularly distinctive rock units that allow identification of the same unit in different areas.

19.          Guide/Index fossils have a wide geographic range and short time of existence.

Multiple Choice:

20.           The forces and processes that can be observed shaping our present day landscapes have also operated in the geologic past. The preceding statement refers to

a.       uniformitarianism.

b.       catastrophism.

c.       Aristotle's hypothesis.

d.       Ussher's premise.

e.       none of these

21.           The principle of superposition states that

a.       sediments are deposited as essentially horizontal layers

b.       the present is the key to the past

c.       undisturbed sedimentary layers get progressively younger from bottom to top

d.       a fault that cuts a sedimentary rock is younger than the rock

22.           By applying the law of superposition _______ dates can be determined.

a.       conventional

b.       radiometric

c.       relative

d.       isotopic

e.       both relative and radiometric

23.           The era of "ancient life" is the _______ era.

a.       Cenozoic

b.       Precambrian

c.       Neolithic

d.       Mesozoic

e.       none of these

24.           A geologic formation is a series of rock layers that                          .

a.       can be recognized and mapped as a distinctive unit

b.       has approximately the same physical properties

c.       contains the same assemblage of fossils

d.       has all of these properties

25.           The statement "The present is the key to the past" relates to

a.       Catastrophism.

b.       uniformitarianism.

c.       Aristotle's hypothesis.

d.       Tarbuck's theory.

e.       none of these

26.           The subdivision of the geologic time scale that represents the longest time span is called a(n)

a.       Epoch               b.  Era.             c. period.                       d. stage.

27.           Which one of the following represents the smallest expanse of time?

a.       Mesozoic

b.       Cenozoic

c.       Precambrian

d.       Paleozoic

28.           Who is credited with formulating the doctrine of uniformitarianism?

a.       Aristotle

b.       Lyell

c.       Hutton

d.       Powell

e.       Playfair

29.           About 85 percent of geologic time is represented by the time span often called the

a.       Paleozoic.

b.       Stone Age.

c.       Precambrian.

d.       Cretaceous.

e.       Ordovician.

30.           The age of Earth is about

a.       2 billion years.

b.       4.5 million years.

c.       16 million years.

d.       4.5 billion years.

e.       195 million years.

31.           The oldest rocks on Earth are approximately                      years old.

a.       4 thousand   b. 4 million     c. 4 billion   d. 4 trillion

32.           Abundant fossil evidence did not appear in the geologic record until about

a.       5 billion years ago.

b.       6 million years ago.

c.       600 million years ago.

d.       300 million years ago.

e.       3 billion years ago.

33.           Of five undeformed horizontal beds of sedimentary rock, we can say that

a.       the top layer is oldest.

b.       the lowest layer is oldest.

c.       the third layer from the bottom is older than the second layer from the bottom.

d.       there is no way of knowing which layer is oldest.


 

34.           An unconformity is

a.       a layer of sedimentary rock.

b.       a gap in the rock record.

c.       A layer of rock with very unusual fossils.

d.       a period of erosion or non-deposition

e.       Either b or d.

f.         All of the above.

35.          A disconformity occurs where:

a.       the beds are parallel above and below the unconformable contact

b.       the beds above and below the unconformable contact are at angles to one another

c.       sedimentary rocks overlie massive crystalline rocks

d.       all of the above

36.          A nonconformity closely resembles:
          a. fault contact
          b. an intrusive contact
          c. a soil on its parent rock
          d. all of the above

37.          Relative time tells us how long ago an event took place

a.       True

b.       False

38.          Fossils which denote particular short periods of time in the geologic past are termed

a.       Environmental indicators.

b.       fossil discriminators.

c.       Huttonian fossils.

d.       Index or guide fossils.

e.       none of these

39.           The principle of fossil succession states that:
          a. the same sequence of life forms repeats over and over
          b. there has been a change in life forms through time
          c. that different assemblages of fossils indicate different geologic ages
          d. answers b. and c.

40.           In order to match rocks of similar age in different regions or to demonstrate age equivalency of rock units, geologists use

a.       Lateral tracing

b.       Radiometric dating

c.       Fossils.

d.       sequence of beds.

e.       All of these.

f.         Similarity of rock type.

g.       None of these.

41.           Which of the following is used by geologists to determine the relative ages in a rock sequence?
          a. stratigraphy
          b. fossils
          c. cross-cutting relations
          d. all of these

42.           Placing geologic events in sequential order as determined by their position in the rock record is called:
          a. absolute dating
          b. uniformitarianism
          c. relative dating
          d. correlation
          e. historical dating

43.           Which one of the following lists places the division of geologic time in order from shortest to longest?

a.       era, period, epoch

b.       epoch, period, era

c.       period, epoch, era

d.       epoch, era, period

e.       none of these


 

44.           About what percent of geologic time is represented by written, recorded human history?

a.       Less than 0.01%

b.       Approximately 1%

c.       Approximately 10%

d.       Approximately 100%

e.       none of these

45.           In undisturbed sedimentary deposits, the youngest beds:
          a. are water beds
          b. are on the top
          c. are on the bottom
          d. could be answers b. or c.

46.           The principle of original horizontality states that:

a.       in most cases sedimentary beds are deposited as horizontal units

b.       in rare cases, horizontality of rock layers occurs.

c.       in most cases, if the beds are inclined, this tilting occurred after the beds were deposited

d.       answers a. and c.

47.           Which of the following is related to relative dating?

a.       cross-cutting

b.       inclusions

c.       superposition

d.       all of these

e.       both inclusions and superposition

48.           When tilted or folded sedimentary rocks are overlain by more flat-lying strata a _______ is said to exist.

a.       disconformity

b.       angular unconformity

c.       nonconformity

d.       conformity

e.       none of these

49.           A layer of sandstone is in contact with a mass of granite. The sandstone contains small pieces of the granite. Which rock is older?

a.       sandstone

b.       granite

c.       both are the same age

d.       it is not possible to determine which is older from the information provided.

50.           Which relative dating principle is illustrated in the preceding question?

a.       cross-cutting

b.       original horizontality

c.       inclusions

d.       superposition

e.       none of the above

51.           An undeformed sedimentary layer is _______ than the layer above and _______ than the layer below.

a.       older, younger

b.       younger, older

c.       younger, younger

d.       older, older

52.           Which of the following processes removes carbon dioxide from the atmosphere?

a.       photosynthesis

b.       volcanic eruptions

c.       weathering of organic carbon

d.       all of these

53.           Assume that you have just examined several flat-lying sedimentary layers. After much study you determine that there is a considerable span of time for which no sedimentary rock layer exists at this site. You have just discovered a(n)

a.       angular unconformity.

b.       series of conformable strata.

c.       disconformity.

d.       example of cross-cutting relationships.


 

54.           A worm would stand a poor chance of being fossilized because

a.       worms have been rare during the geologic past.

b.       worms have no hard parts.

c.       worms contain no carbon-14.

d.       all of these

e.       none of these

55.           The era known as the "age of mammals" or “recent life” is the

a.       Precambrian.

b.       Paleozoic

c.       Cenozoic

d.       Devonian

e.       Silurian

56.           What era is sometimes called the "age of dinosaurs"?

a.       Pleistocene

b.       Cenozoic

c.       Cretaceous

d.       Mesozoic

e.       none of these

57.           The oldest rock in the Grand Canyon is the                         .

a.       Bright Angel Shale

b.       Tapeats Sandstone

c.       Vishnu Schist

d.       Coconino Sandstone

58.           Radioactive decay:
          a. produces heat
          b. produces a transformation from one element to another
          c. answers a. and b.
          d. cannot be used to date rocks because the decay rate is not constant

59.          Radioactive dates are based on:
          a. the ratio of unstable parent material and stable daughter product present in a
sample
          b. measuring the amount of unstable isotopes present
          c. measuring the number of atoms that decay per unit time
          d. none of these

60.          Half life:
          a. is the time necessary for one half of the parent material to decay
          b. times can be very short or very long
          c. times are constant for a given element
          d. all of the above

61.          Radioactive dates are most often determined for:
          a. igneous rocks
          b. sedimentary rocks
          c. metamorphic rocks
          d. glassy rocks

62.          Radioactive carbon dates are useful for the past:
          a. 5000 years
          b. 50,000 years
          c. 70,000 years
          d. none of the above

63.           One type of radioactive decay involves the capture of an electron by a nucleus. When this occurs

a.       the atomic number increases by 1.

b.       the atomic number decreases by 1.

c.       the mass number increases by 1.

d.       the atomic number and the mass number both increase by 1.

e.       the atomic number decreases by 1 and the mass number increases by 1.

64.           An alpha particle consists of

a.       one electron.

b.       two electrons and two neutrons.

c.       two protons and two neutrons.

d.       either b. or c.

e.       none of these


 

65.           When an alpha particle is emitted, how do the mass number and atomic number change, if at all?

a.       mass number 4 less, atomic number 2 less

b.       mass number 2 less, atomic number 2 less

c.       mass number 4 less, atomic number unchanged

d.       mass number 4 less, atomic number 2 higher

e.       none of these

66.           When potassium-40 decays to argon-40, it does so by means of

a.       beta particle emission.

b.       electron capture.

c.       alpha particle emission.

d.       both beta particle emission and electron capture.

e.       both electron capture and alpha particle emission.

67.           When seven-eighths (7/8) of a radioactive isotope has decayed to become the stable daughter product, _______ half-lives have elapsed.

a.       one

b.       two

c.       three

d.       four

e.       none of these

68.           Assume that the half-life of a particular radioactive isotope is 10,000 years. Laboratory analysis shows that the ratio of radioactive parent to stable daughter product in a sample is 1:7. In other words, there is one parent isotope for every 7 daughter isotopes.  What is the age of the sample?

a.       1428.6 years

b.       10,000 years

c.       20,000 years

d.       30,000 years

e.       none of these

69.          Which of the following materials might be dated using carbon-14?

a.       sandstone    b. wood   c. iron ore   d. granite

70.           If a rock is heated during metamorphism and the parent atoms migrate out of a mineral that is subsequently radiometrically dated, an inaccurate date will be obtained. This date will be                   the actual date.
          a. younger than
          b. older than
          c. the same as
          d. it cannot be determined
          e. none of these

71.           What is being measured in radiometric dating?
          a. the time when the radioactive isotope formed
          b. the time of crystallization of a mineral containing an isotope
          c. the amount of the parent isotope only
          d. when the dated mineral became part of a sedimentary rock
          e. when the stable daughter isotope was formed

72.           If a radioactive element has a half-life of 4 million years, the amount of parent material remaining after 16 million years of decay will be what fraction of the original amount?
          a. 1/32   b. 1/16   c. 1/8   d. 1/4   e. ˝

73.           How many half-lives are required to yield a mineral with 625 atoms of U238 and 19,375 atoms of Pb206?
          a.4    b.5   c.6    d.8   e. 10

74.           Absolute time:
          a. gives a non-specific date to an object
          b. gives a specific date to an object
          c. is only useful if fossils are present
          d. only gives the sequence in which events have taken place

75.           Absolute dates are based on:
          a. fossils
          b. educated estimates
          c. radioactive decay
          d. cross-cutting relationships

 

Refer to the following geologic cross section for the following 4 questions. Units A, B, C, D, and F are sedimentary rocks. Unit E is an igneous rock.

Cross-section of some faulted sedimentary layers

76.   When did the faulting occur?

a.                   after deposition of unit A

b.                   after deposition of unit C and before deposition of unit B 

c.                   after deposition of unit F and before deposition of unit C 

d.                   cannot be determined from the information given

77.   What event happened most recently?

a.                   erosion of part of unit C

b.                   faulting

c.                   deposition of unit C

d.                   deposition of unit F

78.   What type of rock is unit E?

a.                   a dike

b.                   a sill

c.                   a lava flow

d.                   answers b. and c.

e.                   answers a. and c.

79.   Which is the oldest unit?
a. unit A     b. unit C     c. unit E     d. unit F

Use the answer sheet provided in class for the following questions and relative dating problem(s).

80.        A series of intersecting dikes or faults may be placed in proper sequence or order by using the principle of ____________.

81.        When one rock mass contains fragments of an adjacent rock mass, we know the adjacent rock mass must be older. The fragments used for relative dating in this situation are generally known as ____________.

82.        An unconformity in which the strata on either side are essentially parallel is termed a (n) ____________.

83.        An unconformity in which tilted or folded strata are overlain by more flat-laying layers is known as a (n) _____________ unconformity.

84.        What is the name of a Phanerozoic era that means ancient life?

85.        The principle of ____________ states that fossil organisms succeed one another in a definite and determinable order and that a time period can be recognized by its fossil content.

86.        Dinosaurs lived during the ____________ era.

87.        Fossils used for matching rocks of the same age are called ____________.

88.        "This dike is 10 million years old." The preceding statement is an example of a (n) ___________ date.  Use the terms that you have been learning in class!

89.        The phrase, "The present is the key to the past," refers to the doctrine of ____________.

90.        The remains or traces of prehistoric life are called ____________.

91.        ____________ dating occurs when events are placed in their proper sequence or order without knowing their numerical ages.

92.        For a radioactive isotope like U-235, what does the 235 indicate?

93.        Give the mass number of the naturally produced, radioactive carbon isotope.

94.        In an un-deformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below. The preceding is a statement of the principle of ____________.

95.        What general term denotes a buried erosional surface?

96.        Fossil A Ranges in Age from the Mississippian to the Pennsylvanian, Fossil B Ranges in age from the Devonian to the Permian, and Fossil C ranges in age from the Permian to the Pennsylvanian.  In what period/sub-period (whichever represents the smaller increment of time) did all three fossils exist at the same time?

97.        See Answer Sheet and the figure below:

 

Cross-section of various rocks, faults, unconformities, etc.

 

 

 

 

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