Question 1

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.

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Question 2

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

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Question 3

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.

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Question 4

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

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Question 5

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.

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Question 6

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

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Question 7

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

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Question 8

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.

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Question 9

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 ____________________.

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Question 10

____________________ dating is used to obtain absolute age dates.

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Question 11

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

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Question 12

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?

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Question 13

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

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Question 14

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

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Question 15

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?

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Question 16

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.

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Question 17

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

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Question 18

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

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Question 19

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

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Question 20

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

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Quiz 17: Geologic Time: Concepts and Principles