Chapter 10 Vocab

Question 1

Cambrian Explosion

Answer 1

The remarkable diversification of life, indicated by the fossil record, that occurred at the beginning of the Cambrian Period.

Question 2

Closure Temperature

Answer 2

The temperature below which isotopes are no longer free to move.

Question 3

Contact

Answer 3

The boundary surface between two rock bodies (as between two stratigraphic formations, between an igneous intrusion and adjacent rock, between two igneous rock bodies, or between rocks juxtaposed by a fault).

Question 4

Correlation

Answer 4

The process of defining the age relations between the strata at one locality and the strata at another.

Question 5

Cross-Cutting Relations

Answer 5

If one geologic feature cuts across another, the feature that has been cut is older.

Question 6

Daughter Isotope

Answer 6

The decay product of radioactive decay.

Question 7

Eon

Answer 7

The largest subdivision of geologic time.

Question 8

Epoch

Answer 8

An interval of geologic time representing the largest subdivision of a period.

Question 9

Era

Answer 9

An interval of geologic time representing the largest subdivision of the Phanerozoic Eon.

Question 10

Fossil Assemblage

Answer 10

A group of fossil species found in a specific sequence of sedimentary rock.

Question 11

Fossil Succession

Answer 11

In a stratigraphic sequence, different species of fossil organisms appear in a definite order; once a fossil species disappears in a sequence of strata, it never reappears higher in the sequence.

Question 12

Geochronology

Answer 12

The science of dating geologic events in years.

Question 13

Geologic Column

Answer 13

A composite stratigraphic chart that represents the entirety of the Earth’s history.

Question 14

Geologic History

Answer 14

The sequence of geologic events that has taken place in a region.

Question 15

Geologic Map

Answer 15

A map showing the distribution of rock units and structures across a region.

Question 16

Geologic Time

Answer 16

The span of time since the formation of the Earth.

Question 17

Geologic Time Scale

Answer 17

A scale that describes the intervals of geologic time.

Question 18

Half-Life

Answer 18

The time it takes for half of a group of a radioactive element’s isotopes to decay.

Question 19

Index Fossil

Answer 19

Widespread fossil species which survived only for a relatively short interval of geologic time.

Question 20

Isotope

Answer 20

Different versions of a given element that have the same atomic number but different atomic weights.

Question 21

Isotopic Dating

Answer 21

The science of dating geologic events in years by measuring the ratio of parent radioactive atoms to daughter product atoms.

Question 22

Original Horizontality

Answer 22

Layers of sediment, when originally deposited, are fairly horizontal.

Question 23

Parent Isotope

Answer 23

A radioactive isotope that undergoes decay.

Question 24

Period

Answer 24

An interval of geologic time representing a subdivision of a geologic era.

Question 25

Precambrian

Answer 25

The interval of geologic time between Earth’s formation about 4.57 Ga and the beginning of the Phanerozoic Eon 542 Ma.

Question 26

Radioactive Decay

Answer 26

The process by which a radioactive atom undergoes fission or releases particles, thereby being transformed into a new element.

Question 27

Relative Age

Answer 27

The age of one geologic feature with respect to another.

Question 28

Stratigraphic Column

Answer 28

A cross-section diagram of a sequence of strata summarizing information about the sequence.

Question 29

Stratigraphic Formation

Answer 29

A recognizable layer of a specific sedimentary rock type or set of rock types, deposited during a certain time interval, that can be traced over a broad region.

Question 30

Stratigraphic Group

Answer 30

Several adjacent stratigraphic formations in a succession.

Question 31

Superposition

Answer 31

In a sequence of sedimentary rock layers, each layer must be younger than the one below, for a layer of sediment cannot accumulate unless there is already a substrate on which it can collect.

Question 32

Unconformity

Answer 32

A boundary between two different rock sequences representing an interval of time during which new strata were not deposited and/or were eroded.

Question 33

Uniformitarianism

Answer 33

Theory that states that physical processes we observe operating today operated in the past, at roughly comparable rates so, the present is the key to the past.