Chapter 8

Question 1

Age of the Earth

Answer 1

prior to 19th century age of Earth was based on religious beliefs: bible says approximately 6000 years, and Chinese and Hindu beliefs say its old beyond comprehension

Question 2

James Hutton

Answer 2

“father of geology,” realized geologic processes require vast amounts of time

Question 3

Charles Lyell

Answer 3

popularized Hutton’s concepts in book Principles of Geology

Question 4

Relative Age

Answer 4

the order of events or objects from oldest to youngest: original horizonality, superposition, lateral continuity,
cross-cutting relationships, inclusions, uncomformities, and correlation

Question 5

Numerical Age

Answer 5

the age of events or objects expressed as a number or numbers: determined using radiometric dating

Question 6

Radiometric Dating

Answer 6

determining how much radioactive decay of a specific element has occurred since a rock formed or an event occurred

Question 7

Contacts

Answer 7

surfaces separating successive rock layers (beds)

Question 8

Formations

Answer 8

bodies of rock of considerable thickness with recognizable characteristics allowing them to be distinguished from adjacent rock layers

Question 9

Original Horizonality

Answer 9

beds of sediment deposited in water are initially formed as horizontal or nearly horizontal layers

Question 10

Superposition

Answer 10

within an undisturbed sequence of sedimentary or volcanic rocks, layers get younger from bottom to top

Question 11

Lateral Continuity

Answer 11

original horizontal layer extends laterally until it tapers or thins at its edges

Question 12

Cross Cutting Relationships

Answer 12

a disrupted pattern is older than the cause of the disruption: intrusions and faults are younger than the rocks they cut through

Question 13

Baked Contacts

Answer 13

contacts between igneous intrusions and surrounding rocks, where surrounding rocks have experienced contact metamorphism

Question 14

Inclusions

Answer 14

fragments embedded in host rock are older than the host rock

Question 15

Uncomformity

Answer 15

a surface (or contact) that represents a gap in the geologic record

Question 16

Disconformity

Answer 16

an unconformity in which the contact representing missing rock layers separates beds that are parallel to each other

Question 17

Angular Uncomformity

Answer 17

an unconformity in which the contact separates overlying younger layers from eroded tilted or folder layers

Question 18

Nonconformity

Answer 18

an unconformity in which an erosional surface on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rock: plutonic and metamorphic rocks exposed by large amounts of erosion, and it typically represents a large gap in the geologic record

Question 19

Correlation

Answer 19

The determination of the time-equivalency of rock units, matching of rocks of similar ages in different regions

Question 20

Physical Continuity

Answer 20

physically tracing a continuous exposure of a rock unit

Question 21

Similarity of Rock Types

Answer 21

assumes similar sequences of rocks formed at same time, and can be inaccurate if very common rock types are involved

Question 22

Correlation by Fossils

Answer 22

fossil species succeed one another through the layers in a predictable order

Question 23

Fossils

Answer 23

Evidence of past life, traces or remains of prehistoric life now preserved in rock. They are generally found in sediment or sedimentary rock (rarely in metamorphic and never in igneous rock)

Question 24

Paleontology

Answer 24

study of fossils

Question 25

Geologic Importance of Fossils

Answer 25

They aid in interpretation of the geologic past, serve as important time indicators, and allow for correlation of rocks from different places

Question 26

William Smith

Answer 26

noted that sedimentary strata in widely separated area could be identified and correlated by their distinctive fossil content

Question 27

Fossil Succession

Answer 27

fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content

Question 28

Index Fossil

Answer 28

geographically widespread fossil that is limited to a short span of geologic time

Question 29

Geologic Time Scale

Answer 29

It is a worldwide relative time scale, it subdivides geologic time based on fossil assemblages, and is divided into eons, eras, periods, and epochs

Question 30

Precambrian

Answer 30

represents 87% of geologic time

Question 31

Paleozoic Era

Answer 31

“Old Life” notes the appearance of complex life

Question 32

Mesozoic Era

Answer 32

“Middle Life” dinosaurs were abundant and the era was ended by mass extinction

Question 33

Cenozoic Era

Answer 33

“New Life” mammals and birds are abundant, the most recent ice ages occurred during the Pleistocene Epoch of the Quaternary Period

Question 34

Numerical Dating

Answer 34

puts absolute values (e.g., millions of years) on the ages of rocks and geologic time periods: it uses radioactive decay of unstable isotopes, and has only possible since radioactivity was discovered in 1896

Question 35

Nucleus

Answer 35

made up of protons, positively charged particles with mass, and neutrons, neutral particles with mass

Question 36

Electrons

Answer 36

negatively charged particles that orbit the nucleus

Question 37

Atomic Number

Answer 37

Element’s identifying number and is equal to the number of protons

Question 38

Mass number

Answer 38

Sum of the number of protons and neutrons

Question 39

Isotope

Answer 39

variant of the same parent atom, differs in the number of neutrons, results in a different mass number than parent atom

Question 40

Radioactivity

Answer 40

Spontaneous changes (decay) in the structure of atomic nuclei