GEOLOGIC TIME

Question 1

A radioactive isotope of the element potassium decays to produce argon. If the ratio of the number of argon to potassium atoms is found to be 7:1, how many half-lives have occurred since the sample of radioactive potassium started to decay?

Answer 1

3

Question 2

The determination that one feature is older or younger than another feature, without calculating their actual ages, is known as

Answer 2

relative dating.

Question 3

If a sandstone contains pieces of basalt, then the sandstone is younger than the basalt according to the principle of

Answer 3

inclusions

Question 4

An area of slightly dipping sedimentary rock layers has large inclusions and is intruded by an igneous dike. Using the basic principles for determining relative ages you can infer that the

Answer 4

sedimentary rock “baked” by the igneous intrusion is older than the intrusion.

Question 5

Footprints, feeding traces, burrows, and dung are considered to be

Answer 5

trace fossils.

Question 6

The age of beds exposed in one location is related to the age of beds exposed in another location based on similarities in rock type between the two locations. What is this process called?

Answer 6

Lithologic correlation

Question 7

Which principle states that in an undisturbed sedimentary sequence, the oldest layer lies at the bottom and the youngest layer at the top?

Answer 7

Principle of superposition

Question 8

An organism is most likely to be fossilized if it

Answer 8

dies in an oxygen-poor environment.

Question 9

What type of unconformity is illustrated by the sequence?

Answer 9

Angular unconformity

Question 10

Geologists estimate that the Earth is 4.54 billion years old, based on

Answer 10

isotopic dating of meteorites from the first differentiated bodies of the Solar System.

Question 11

Uniformitarianism means

Answer 11

geologic processes that operate today operated in the past at about the same speed.

Question 12

Petrified wood is an example of a

Answer 12

permineralized fossil.

Question 13

The concept that times of relative stability in the number and identity of species alternate with times of rapid change is called

Answer 13

punctuated equilibrium.

Question 14

The observations of _____________ led to the principle of uniformitarianism.

Answer 14

James Hutton

Question 15

The image shows a stratigraphic section of the Grand Canyon. Between which two groups is there an angular unconformity?

Answer 15

Unkar Group and Tapeats Sandstone

Question 16

The surface below sedimentary rocks that overlie igneous or metamorphic rocks is termed a(n)

Answer 16

nonconformity

Question 17

According to the following image, after one half-life has passed, what is the ratio of parent isotopes to daughter isotopes?

Answer 17

8:8

Question 18

Unconformities represent __________ in the rock record.

Answer 18

erosion or nondeposition

Question 19

A tilted sequence of sedimentary rocks violates which principle?

Answer 19

original horizontality

Question 20

In the following image of the Grand Canyon, identify the nonconformity.

Answer 20

D

Question 21

Which of the following is always the same for different isotopes of a single element?

Answer 21

atomic number

Question 22

If a basalt body cuts across a fault, what are the relative ages of the basalt and the fault?

Answer 22

The fault must be older, according to the principle of cross-cutting relationships.

Question 23

How is the half-life of a radioactive parent isotope defined?

Answer 23

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

Question 24

Several geologic principles are used to determine __________ ages.

Answer 24

relative

Question 25

In an undisturbed sequence of sedimentary rocks, younger layers overlie older layers, according to the principle of

Answer 25

superposition

Question 26

Two layers of rock contain trilobites that have the same body morphology; however, one rock layer is a shale and the other is an ironstone. Can these two layers be used for correlation?

Answer 26

Yes, if the trilobites are the same, then the layers were formed at the same time.

Question 27

If horizontal sedimentary strata overlie tilted strata (and no fault is present), the eroded surface between the horizontal and tilted strata must be a(n)

Answer 27

angular unconformity.

Question 28

Two atoms of a single element that differ in number of neutrons are said to represent two distinct __________ of that element.

Answer 28

isotopes

Question 29

Buried erosional surfaces between parallel sedimentary strata are termed

Answer 29

disconformities

Question 30

A(n) __________ contact surrounds a pluton.

Answer 30

baked

Question 31

A basaltic lava flow contains fragments of sedimentary rocks. Which of the following statements is true regarding their relative ages?

Answer 31

The lava flow is younger than the sedimentary rock.

Question 32

If the ratio of parent to daughter isotopes is 25:75, how many half-lives have passed?

Answer 32

2

Question 33

Uniformitarianism is succinctly summarized by which phrase?

Answer 33

The present is the key to the past.

Question 34

The geologic time scale is broken into a series of eras, epochs, and periods based mainly on the fossils found in each section. This is an example of __________ dating.

Answer 34

relative age

Question 35

Within the world’s sedimentary rocks, fossils

Answer 35

occur in an ordered sequence.