Deck 17: Geologic Time: Concepts and Principles

Question 1

What are the six fundamental geologic principles which are used in relative dating?

Answer 1

superposition,original horizontality,lateral continuity,cross-cutting relationships,inclusions,fossil succession

Question 2

What is the principle of uniformitarianism? Why does the principle of uniformitarianism lead to the conclusion that Earth's age is great?

Answer 2

Present-day processes have operated throughout geologic time; the laws of physics,chemistry,and biology have operated throughout geologic time.Geologists can observe that the processes which are currently shaping,and previously shaped,Earth occur very slowly or infrequently and cannot be accommodated by an historic time scale.

Question 3

Explain why correlation by fossils is necessary to demonstrate time equivalence of strata.

Answer 3

Each life form is indicative of a specific interval of geologic time.

Question 4

What criteria are used to correlate rock units in different areas?

Question 5

What is the goal of subsurface correlation techniques that is used in the search for oil and gas?

Question 6

A clast of granite taken from a conglomerate is determined by radiometric dating to be one hundred million years old.What,if anything,does this tell you about the age of the conglomerate?

Question 7

Why was Lord Kelvin's argument for the age of Earth fundamentally in error?

Question 8

Earlier Precambrian rocks could not be correlated over great distances from one area to another (e.g.,from Canada to Europe)but younger rocks were correlated in the same areas with a high degree of confidence.Why was this?

Question 9

Why don't the sources of uncertainty in radiometric dating invalidate or lend suspicion to the results obtained?

Question 10

What fact makes radiocarbon dating possible?

Question 11

Describe how stalagmites are used to reconstruct past climate.

Question 12

What are the requirements for a useful guide fossil?

Question 13

What is the principle of superposition,and what is its importance? Who is credited with discovering it?

Question 14

What is the principle of fossil succession,and what is its importance? Who is credited its discovery?

Question 15

Why is it necessary to employ lithologic and fossil correlation to establish a relative sequence of geologic time?

Question 16

What are seismic profiles?

Question 17

What types of deposits are considered marker beds? What is the importance of a marker bed?

Question 18

How does relative dating differ from absolute dating?

Question 19

How are zones of rocks that are deposited during equivalent time intervals constructed using fossil assemblages?

Question 20

How does the sequence of events differ between an angular unconformity and a disconformity?

Question 21

A sedimentary rock that shows evidence of contact metamorphism must be ____________________ in age than the igneous rock with which it is in contact,even if it lies above the igneous rock.

Question 22

Long-lived radioactive isotope pairs used in radiometric dating have half-lives of the magnitude of ____________________ or ____________________ of years.

Question 23

Fragments of a rock that are contained in a layer of another rock must be ____________________ in age than the layer of rock which surrounds them.

Question 24

An interval of geologic time not represented by strata in a particular area is a(n)____________________.

Question 25

The principle of ____________________ states that rock layers extend laterally in all directions unless or until they terminate in one of a number of natural means.

Question 26

To determine the age of sedimentary rocks containing fossils,____________________ zones are established,plotting the overlapping geologic ranges of different species of fossils.

Question 27

The most accurate radiometric dates are obtained from ____________________ rocks.Only in very unusual circumstances can ____________________ rocks be radiometrically dated.

Question 28

The half-life of a radioactive element is the amount of time it takes for ____________________ of the atoms of the unstable ____________________ element to decay to atoms of a new,more stable ____________________ element.

Question 29

The time necessary for half of the atoms of the unstable parent element to decay to the new,more stable daughter element is the isotope's ____________________.

Question 30

____________________ dating is used to obtain absolute age dates.

Question 31

Prior to the discovery of radioactivity in the late ______ century,geologists were able to develop a(n)____________________ geologic time scale.

Question 32

If the dating technique is used correctly,how reliable are the radiometric dates derived from individual layers of stalagmites using ratios of uranium 234 to thorium 230?

Question 33

Different varieties of an atom that have a different number of neutrons in their nuclei are ____________________.

Question 34

What kind of rocks (igneous,sedimentary,metamorphic)have been most important in determining absolute age dates for the geologic time scale? Explain why.

Question 35

How are marker beds used to determine the age of strata in a region that has no marker beds but does contain strata with the same fossil assemblage zone?

Question 36

In order to correlate age-equivalent rock units of dissimilar composition or to correlate rock units over a large area,____________________ and the principle of ____________________ must be used.

Question 37

A body of rock that is intruded by another rock must be ____________________ in age than the intrusion.

Question 38

Which of the major rock types were most important originally in developing the geologic time scale,and why?

Question 39

The placement of events into a sequential order based upon their position in the rock record is referred to as ____________________ dating.

Question 40

A surface of discontinuity representing a break in the depositional record or a discontinuity representing erosion or nondeposition is a(n)____________________.

Question 41

Whose work was the basis for the principle of uniformitarianism and the unavoidable necessity of a great age for Earth?

A) Charles Lyell
B) William Smith
C) James Hutton
D) Lord Kelvin
E) John Joly

Question 42

Lithostratigraphic units are defined by physical attributes of the rocks.

Question 43

Climate changes in a region because

A) continents are carried to different latitudes.
B) continental movement affects ocean circulation patterns.
C) continental movement affects atmospheric circulation patterns.
D) all of these.

Question 44

Sources of uncertainty in radioactive dating do not include ____.

A) loss of daughter isotope
B) uncertainty in decay constants
C) experimental and sample error
D) addition of parent isotope
E) questions about metamorphism

Question 45

Once the concept of a linear time and history were established,the earliest estimates of Earth's age were based on ____.

A) inference from the Bible
B) inference from the rates of observable geologic processes
C) direct statements from the Bible
D) faith
E) none of these

Question 46

Stalagmites can be radiometrically dated because

A) like tree rings, the calcium carbonate layers vary in thickness by year.
B) carbon-14 decays to nitrogen 14 in the carbonate.
C) uranium-234 substitutes for calcium and decays to thorium-230.
D) fission tracks in apatite in the structures can be dated.

Question 47

Fossils cannot usually be dated directly because they are not composed of minerals that naturally contain radioactive isotopes.

Question 48

A fossil that is particularly useful for correlation is an evolutionary fossil.

Question 49

Which principle states that fossil assemblages succeed one another through time in a regular and predictable order?

A) principle of cross-cutting relationships
B) principle of inclusions
C) principle of fossil succession
D) principle of uniformitarianism
E) principle of superposition

Question 50

What is the loss of two protons and two neutrons from the nucleus called?

A) alpha decay
B) beta decay
C) electron decay
D) electron capture
E) half-life decay

Question 51

The time equivalence of strata is determined by ____.

A) correlation of unusual lithologies
B) correlation of key beds
C) correlation of fossils
D) lateral tracing
E) superposition

Question 52

If an isotope has a half-life of 50 million years,and 1/8 of the sample remaining consists of that isotope,what is the age of the rock from which it was taken?

A) 400 million years
B) 300 million years
C) 150 million years
D) 800 million years
E) none of these

Question 53

The geologic time scale was initially put together by

A) radiometric dating and correlation.
B) superposition, fossil succession and correlation.
C) lithostratigraphy and biostratigraphy.
D) carbon-14 age dating and lithostratigraphy.

Question 54

What principle states that in an undisturbed succession of sedimentary rocks,the oldest layer is at the bottom and the youngest is at the top?

A) principle of cross-cutting relationships
B) principle of inclusions
C) principle of fossil succession
D) principle of uniformitarianism
E) principle of superposition

Question 55

What is the approximate length of time preserved in Grand Canyon rocks?

A) 10,000 years
B) 100,000 years
C) 1 million years
D) 1 billion years
E) 10 billion years

Question 56

What principle states that fragments of one rock contained within another rock are older than the containing rock?

A) principle of cross-cutting relationships
B) principle of inclusions
C) principle of fossil succession
D) principle of uniformitarianism
E) principle of superposition

Question 57

A surface of erosion on metamorphic or igneous rocks,below sedimentary rocks is a(n)____.

A) nonconformity
B) disconformity
C) angular unconformity
D) anticonformity
E) none of these

Question 58

Who,by virtue of a mathematical model,concluded that Earth could not be older than 100 million years and no younger than 20 million years?

A) Charles Lyell
B) William Smith
C) James Hutton
D) Lord Kelvin
E) John Joly

Question 59

What is the age of the Earth?

A) 12.6 billion years
B) 12.6 million years
C) 4.6 billion years
D) 4.6 million years
E) 10,000 years

Question 60

What is the maximum age limit for radiocarbon dating of fossils?

A) 70,000 years
B) 700,000 years
C) 7 million years
D) 70 million years
E) 700 million years

Question 61

The fossils of plants and animals indicate something about the environment and climate at the time the organisms were living.

Question 62

Biostratigraphic units are defined by fossil content.

Question 63

Geologists are correlating past geologic events to see if there are correlations with climate changes.

Question 64

Stratigraphy is the study of the composition,origin,aereal distribution and age relationships of layered rocks.

Question 65

The basic lithostratigraphic unit is the series.

Question 66

Denver 280 million years ago was covered by glaciers.

Question 67

Time-stratigraphic units are units of rock sharing a specific lithology.