Week 1 Quiz - geological time

Question 1

Seasonal changes create layering in glaciers known as

Answer 1

rhythmic layering

Question 2

Numerical ages for boundaries between time units on the geologic time scale primarily resulted from the study of ________, in conjunction with relative age data.

Answer 2

radiometric dating of igneous rocks

Question 3

Uniformitarianism is succinctly summarized by:

Answer 3

The present is the key to the past

Question 4

A radiometric age for a mineral crystal within an igneous rock measures the amount of time that has passed since the ________.

Answer 4

temperature of the crystal became equal to the closure temperature for the mineral

Question 5

Magma has intruded into some limestone, and a marble rind formed surrounding the granite pluton. The marble rind must be younger than the limestone according to the principle of ________.

Answer 5

baked contacts

Question 6

Radiometric dates applied to sedimentary rocks produce ages that ________.

Answer 6

are too old (predate sedimentary deposition)

Question 7

Basaltic clasts within a conglomerate have been radiometrically dated to 50 million years ago. Is this a reliable age for the conglomerate?

Answer 7

No, this age is likely too old.

Question 8

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

Answer 8

angular unconformity

Question 9

In an unweathered sample of igneous rock, the ratio of an unstable isotope to its stable daughter isotope is 1:15. If no daughters were present at the time the rock cooled below closure temperature, and the half-life of the isotope is 50 million years, how old is the rock?

Answer 9

200 million years

Question 10

Why is radiocarbon dating only rarely applied in geological work?

Answer 10

The half-life of carbon-14 is so short that it can only be used to date materials that are less than 70,000 years old.

Question 11

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

Answer 11

nonconformity

Question 12

If the lithology and fossil content of two bodies of rock on opposite sides of a canyon are identical, then these remaining outcrops were likely physically connected at one time and formed part of an extensive, sheet-like layer of rock. This idea summarizes the principle of ________.

Answer 12

original continuity

Question 13

How much of a radioactive parent isotope will remain after three half-lives have passed?

Answer 13

one-eighth

Question 14

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

Answer 14

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

Question 15

When an unstable parent isotope decays

Answer 15

The daughter isotope may continue to decay

Question 16

The closure temperature represents the point when ________.

Answer 16

isotopes are no longer free to move out of a crystal lattice

Question 17

Buried erosional surfaces between parallel sedimentary strata are termed ________.

Answer 17

disconformities

Question 18

Basaltic clasts within the basal layers of a conglomerate imply

Answer 18

The basalt must be the older of the two.

Question 19

As understood by modern geologists, the principle of uniformitarianism implies that ________.

Answer 19

physical processes observed today (such as erosion and volcanic eruption) have been active in the past and are preserved in the rock record

Question 21

What geological principle is a direct result of gravity

Answer 21

original horizontality

Question 22

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

Answer 22

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

Question 23

What geological principle is not a result of gravity

Answer 23

Cross-cutting relationships

Question 24

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

Answer 24

superposition