Deck 18: Geologic Time

Question 1

An unconformity is a buried _.

A)surface of erosion with older strata above and younger strata below
B)fault or fracture with younger strata above and older strata below
C)surface of erosion separating younger strata above from older strata below
D)fault or fracture with older rocks above and younger rocks below

Answer 1

C

Question 2

Which of the following geologic observations would not bear directly on working out the sequence of geologic events in an area?

A)an unconformity between a granite and sandstone
B)inclusions of sandstone in a granite pluton
C)the feldspar and quartz contents of a granite
D)a well- exposed dike of basalt in sandstone

Answer 2

C

Question 3

The ratio of parent to daughter isotopes in a radioactive decay process is 0.40. How many half- lives have elapsed since the material was 100% parent atoms?

A)less than l
B)between l and 2
C)between 2 and 3
D)more than 3

Answer 3

B

Question 4

Who made the first clear statement of the law of superposition? When?

A)John Wesley Powell, nineteenth century
B)Nicolaus Steno, seventeenth century
C)John Stuart Priestly, nineteenth century
D)William Smith, eighteenth century

Question 5

What is the age of the Earth accepted by most scientists today?

A)4.5 billion years
B)6.4 million years
C)6.4 billion years
D)4.5 million years

Question 6

Which of the following denotes the divisions of the geologic time scale in correct order of decreasing lengths of time beginning with the longest time interval and ending with the shortest?

A)eon, epoch, period, era
B)eon, era, period, epoch
C)eon, era, epoch, period
D)era, period, epoch, eon

Question 7

When a radioactive isotope decays by electron capture, the electron .

A)combines with a neutron in the nucleus, raising the mass number of the daughter isotope by one
B)makes the daughter isotope into an ion with a charge of positive one
C)combines with a proton in the nucleus; the atomic number of the daughter is one less than the parent
D)makes the parent isotope into an ion with a charge of negative one

Question 8

The half- life of carbon- 14 is about 6000 years. Assume that a sample of charcoal formed by burning of living wood 15,000 years ago. How much of the original carbon- 14 would remain today?

A)more than 50%
B)between 25% and 50%
C)between 12.5% and 25%
D)between 33% and 50%

Question 9

Which of the following refers to the investigative process by which geologists identify and match sedimentary strata and other rocks of the same ages in different areas?

A)cross- access dating
B)super matching
C)strata indexing
D)correlation

Question 10

Consider the names of the eras in the geologic time scale. What is meant by "zoic"?

A)life; living things
B)time; recording of events
C)places; geographic references
D)rocks; lithified strata

Question 11

Which of the following is not a very long- lived, radioactive isotope?

A)Rb- 87
B)K- 40
C)C- 14
D)U- 238

Question 12

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

A)worms contain no carbon- 14
B)worms have no hard parts
C)worms have been rare during the geologic past
D)all of these

Question 13

By applying the law of superposition dates can be determined.

A)conventional
B)relative
C)radiometric
D)both relative and radiometric

Question 14

The time period of "ancient life" is the era.

A)Paleozoic
B)Phanerozoic
C)Cenozoic
D)Mesozoic

Question 15

Visualize five horizontal sedimentary strata exposed in a cliff or canyon wall identified by consecutive numbers, 1 being the lowest bed and 5 being the highest. Which of the following statements concerning the strata are TRUE?

A)bed 4 is older than bed 2
B)bed 5 is the oldest
C)bed 3 is older than beds 2 and 4
D)beds l and 3 are older than bed 4

Question 16

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)series of conformable strata
B)disconformity
C)angular unconformity
D)example of cross- cutting relationships

Question 17

Assume that man's recorded history can be stretched back to 4600 years before the present. This is approximately what fraction of geologic time?

A)one hundred- thousandth
B)one millionth
C)one billionth
D)one ten- thousandth

Question 18

is an erosional contact between tilted, older strata below and horizontal, younger strata above.

A)Cross cutting
B)A disconformity
C)An angular unconformity
D)Inverse bedding

Question 19

About 88 percent of geologic time is represented by the time span called the .

A)Paleozoic
B)Phanerozoic
C)Mesozoic
D)Precambrian

Question 20

The is the idea or concept that ancient life forms succeeded each other in a definite, evolutionary pattern and that the contained assemblage of fossils can determine geologic ages of strata.

A)law of fossil regression
B)principle of faunal succession
C)law of correlative indexing
D)principle of cross correlation

Question 21

Isotopes of what element are the stable, end products of both uranium decay series?

Question 22

The remains or traces of prehistoric life are called .

Question 23

The general term denotes a buried, erosional surface where rock layers are missing.

Question 24

Who is credited with formulating the doctrine of uniformitarianism?

A)Playfair
B)Lyell
C)Aristotle
D)Hutton

Question 25

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

Question 26

Which of the following is an essential characteristic of an index fossil?

A)The fossils occur in deep- water marine sediments, but the organism actually lived in the sunlit, surface layer of the ocean.
B)The fossil ages can be determined through radiocarbon dating methods.
C)The organism lived only in specific environments such as beaches or estuaries.
D)The organism only lived for a short period of geologic time.

Question 27

Which of the following best characterizes an angular unconformity?

A)Horizontal lava flows lie below the unconformity, and horizontal, sedimentary strata lie above.
B)It is the discordant boundary between older strata and an intrusive body of granite.
C)Tilted strata lie below the unconformity with loose, unconsolidated soil above.
D)Tilted strata lie below the unconformity, and bedding in younger strata above is parallel to the unconformity.

Question 28

What is the inert gas, daughter product of the radioactive isotope, K- 40?

Question 29

Which of the following describes radioactive decay by beta particle emission?

A)The atomic number of the daughter isotope is one more than the parent; the mass numbers are the same.
B)The daughter isotope has an atomic number two less than the parent and a mass number four less.
C)The daughter isotope has an atomic number one less than the parent and a mass number two less.
D)The mass number of the daughter isotope is one more than the parent, and both isotopes have the same atomic number.

Question 30

If the ratio of radioactive parent to stable daughter isotope is 1:3, how many half- lives have elapsed?

Question 31

Sandstone strata and a mass of granite are observed to be in contact. Which of the following statements is correct geologically?

A)The granite is older if the sandstone contains pebbles of the granite.
B)The granite is older if it contains inclusions of sandstone.
C)The sandstone is younger if the granite contains sandstone inclusions.
D)The sandstone is younger if it shows evidence of contact metamorphism.

Question 32

What process involves identifying and matching rocks of similar ages in different areas?

Question 33

What term denotes blocks of older rock enclosed in a body of younger igneous rock?

Question 34

We now live in the era.

Question 35

For a radioactive isotope like Uranium- 235, what does the 235 indicate?

Question 36

What fundamental concept states that in a horizontal sequence of conformable sedimentary strata, each higher bed is younger than the bed below it?

A)law of superposition
B)theory of superstition
C)law of original correlation
D)theory of correlative deposition

Question 37

All of geologic time prior to the beginning of the Paleozoic era is commonly referred to as the .

Question 38

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

Question 39

What kind of unconformity is produced when tilted, older strata are eroded and buried by younger strata?

Question 40

In an undeformed 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 law of .

Question 41

Compare and contrast relative age dating with radiometric age dating. What is a limitation (if any)of each?

Question 42

Examine the illustration below (a cross section through the Earth as you might observe on the wall of a quarry or a road cut). Give two reasons why the granite must be older than the sedimentary layers.

Question 43

In a given area where you have little knowledge of the local geology (rocks types, fossils, etc.), what type of unconformity would be the most difficult to recognize in an exposed sequence of rocks? Why?

Question 44

You are asked to interpret the geologic history of a county in California where the geology is quite complex. Aside from visiting various sites in the county for observing geologic sites firsthand, you are permitted to request five different pieces of information or data to aid in your interpretation. List the five that you would choose and explain why each is important for your study.