chapter 8

Question 1

A(n) _________ is a contact in which an erosional surface on a pluton or metamorphic rock has been covered by sedimentary (or volcanic) rock.
disconformity, basal conglomerate, nonconformity, or angular unconformity.

Answer 1

nonconformity

Question 2

The _____ is the principle says that the same processes and natural laws that operated in the past are those we can actually observe or infer from observation as operating at present.

Answer 2

actualism

Question 3

fossils are common in ___.

Answer 3

sedimentary rocks

Question 4

___ are subdivisions of eras.

Answer 4

periods

Question 5

Our ability to assign an age to geological and archaeological materials is based on our ability to measure the relative abundance of radioactive ___ and their stable decay products.

Answer 5

isotopes

Question 6

The ___ of a radioactive material is the time it takes for a given amount of radioactive isotope to be reduced by half.

Answer 6

half life

Question 7

In radioactive decay a(n) _______ emission is the emission of two neutrons and two protons from a nucleus.

Answer 7

alpha

Question 8

______ denotes the vast amount of time that precedes the Paleozoic Era.

Answer 8

Precambrian

Question 9

The _____ ended with the greatest mass extinction ever to occur on Earth.

Answer 9

Paleozoic Era

Question 10

Uranium-238 ultimately decays to _____ -206

Answer 10

lead

Question 11

In geology, __ usually means determining time equivalency of rock units.

Answer 11

correlation

Question 12

When marine geologists collects a core of undeformed ocean-floor sediment, they know that the youngest layer is on the top of the core and the oldest is at the bottom because of the principle of __.

Answer 12

superposition

Question 13

The proportional amount of atoms that decay with time _____ by the high pressures and temperature of Earth’s interior.

Answer 13

is not changed at all

Question 14

The principle of ___ states that an original sedimentary layer extends laterally until it tapers or thins at is edges

Answer 14

lateral continuity

Question 15

______ first pointed out that fossil species succeed one another through successive layers of sediment in a predictable order.

Answer 15

W.S. Smith

Question 16

how old is the earth

Answer 16

4,500,000,000 to 4,600,000,000 yrs old

Question 17

In a(n) __________ the erosional contact represents missing rock strata and separates sedimentary beds that are parallel.

Answer 17

disconformity

Question 18

In the radioactive decay process of __ decay, an electron is emitted from the nucleus of the parent isotope.

Answer 18

beta

Question 19

A(n) _______ is an erosional surface that represents a gap in the geologic record.

Answer 19

unconformity

Question 20

The truncation of bedding where sedimentary rock layers abut a granite pluton suggests a(n) ______.

Answer 20

intrusive contact

Question 21

In the radioactive decay process of electron capture a(n) ___ in the nucleus captures an orbiting electron.

Answer 21

proton

Question 22

The half-life of the carbon 14 isotope is 5730 years. If there were 4 billion atoms of C-14 in a particular organism at the time it died, how many atoms of C-14 would there be in the remains of that organism 11,460 years after it died?

Answer 22

1 billion

Question 23

Alvarez and others proposed a hypothesis that dinosaur extinction occurred because __.

Answer 23

one or more asteroids impacted Earth, resulting in environmental change

Question 24

By the principle of __, the surface feature known as the Grand Canyon is ___ than the sedimentary formations that are exposed in the side walls of the Grand Canyon.

Answer 24

cross-cutting relationships; younger

Question 25

The principle of ______ states that fragments included in a host rock must be _______ than the host rock.

Answer 25

inclusion; older than

Question 26

The relative-dating principle of __ states that fragments included in a host rock are older than the host rock.

Answer 26

inclusion

Question 27

Radiocarbon dating is useful in dating an event that occurred in the past ________ years.

Answer 27

40 thousand

Question 28

The ____ is based upon the observation that fossil species succeed one another through layers in a predictable order.

Answer 28

principle of faunal succession

Question 29

_______ is the spontaneous nuclear change of isotopes with unstable nuclei.

Answer 29

radioactive decay

Question 30

Isotopic dating has shown that the Precambrian took up ______% of all geologic time

Answer 30

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