Chapter 9 Geologic Time

Front 1

Law of Superposition

Back 1

in undistubed layers of sedimentary rock, the oldest is on the bottom, and the youngest is on the top.

Front 2

Cross-cutting

Back 2

A principle of relative dating. A rock or fault is younger than any rock (or fault) through which it cuts.

Front 3

Which principle or law of geology states that in a sequence of undeformed sedimentary rocks, each bed is older than the one above

Back 3

law of superposition

Front 4

The fact that sedimentary rocks are almost always deposited in a horizontal position reflects which law or principle of geology?

Back 4

original horizontality

Front 5

original horizontality

Back 5

Layers of sediment that are generally deposited in a horizontal or nearly horizontal position.

Front 6

Conformable layers

Back 6

Rock layers that were deposited without interruption.

Front 7

While working in the field, you encounter an outcrop in which sandstone, shale, and limestone have been intruded by a basaltic dike. You know that the basaltic dike is younger than the sedimentary rock by applying which law or principle?

Back 7

the principle of Crosscutting relationships

Front 8

In the field you encounter a sequence of sedimentary rocks that has a dike running through them. A normal fault crosses the entire sequence, cutting off part of the dike near the surface. Which scenario best describes your observations? (All scenarios list events from oldest to youngest.)

Back 8

The relative ages of the sequence are as follows: sedimentary rocks > dike > normal fault.

Front 9

Angular unconformity

Back 9

An unconformity in which the older strata dip at an angle different from that of the younger beds.

Front 10

disconformity

Back 10

A type of unconformity in which the beds above and below are parallel.

Front 11

Nonconformity

Back 11

An unconformity in which older metamorphic or intrusive igneous rocks are overlain by younger sedimentary strata.

Front 12

What term describes an erosional surface bounded above by flat-lying sedimentary rocks and below by igneous or metamorphic rocks?

Back 12

nonconformity

Front 13

Any rock fragments included within another rock must be older than the rock in which they are included. (For example, if eroded fragments of one rock layer become part of another sedimentary rock layer, the rock with the included fragments must be younger than the fragments themselves.)

Back 13

Inclusions

Front 14

Inclusions

Back 14

A piece of one rock unit that is contained within another. Inclusions are used in relative dating. The rock mass adjacent to the one containing the inclusion must have been there first in order to provide the fragment.

Front 15

Numerical date

Back 15

The number of years that have passed since an event occurred. (More specific dating)

Front 16

isotopes

Back 16

Varieties of the same element that have different mass numbers; their nuclei contain the same number of protons but different numbers of neutrons.

Front 17

radioactive decay

Back 17

The spontaneous decay of certain unstable atomic nuclei.

Front 18

alpha particle

Back 18

a particle emitted from an atomic nucleus during radioactive decay, which is positively charged and has two neutrons and two proton

Front 19

Name the three products of radioactive decay

Back 19

electron capture, beta particle and alpha particle;

Front 20

beta particle

Back 20

a fast-moving electron emitted by radioactive decay of substances

Front 21

When a beta particle is emitted what occurs

Back 21

Neutron becomes a Proton

Front 22

For each beta particle emitted how does that effect the mass number

Back 22

no change at all

Front 23

For each beta particle emitted how does that effect the atomic number

Back 23

One greater

Front 24

electron capture

Back 24

a mode of radioactive decay in which an orbital electron is captured by the nucleus. Then the captured electron combines with a proton to form a neutron

Atomic number: 1 more / Atomic mass: no change

Front 25

When an electron is captured by a nucleus how is the mass number effected

Back 25

No change

Front 26

When an electron is captured by a nucleus how is the atomic number effected

Back 26

One fewer

Front 27

half life

Back 27

the time required for one-half of the atoms of a radioactive substance to decay

Front 28

How is the atomic number of an atom determined?

Back 28

counting the number of protons

Front 29

After four half-lives of decay, what is the ratio of radioactive parent isotope to stable daughter isotope?

Back 29

1/15

Front 30

A radioactive element undergoes decay via the loss of two alpha particles to form a stable daughter isotope. Following the decay, what would the atomic number of this newly created stable isotope be?

Back 30

The atomic number of the daughter isotope would be four units less than the original parent isotope.

Front 31

What happens to isotopes during radioactive decay?

Back 31

Parent isotopes turn into daughter isotopes

Front 32

What is the scientific definition of half-life?

Back 32

the amount of time over which the number of parent isotopes decreases by half

Front 33

Two containers hold the same radioactive isotope. Container A contains 1000 atoms, and container B contains 500 atoms. Which has a greater rate of decay

Back 33

Container A (The rate of decay of atoms in container A is greater than the rate of decay of atoms in container B.)

Front 34

A container holds 100 atoms of an isotope. This isotope has a half-life of 1.5 months. How many total atoms will be in the container after 3 months?

Back 34

100 atoms (Atoms of radioactive isotopes turn into atoms of other isotopes.)

Front 35

A container holds 100 atoms of an isotope. This isotope has a half-life of 1.5 months. How many atoms of the radioactive isotope will be in the container after 3 months?

Back 35

25 radioactive isotopes

Front 36

A rock sample contains 75 atoms of a parent isotope and 25 atoms of a daughter isotope. The half-life of the parent isotope is 100 years. How old is this rock?

Back 36

50 years

Front 37

If one half-life has lapsed, what is the radioactive parent to stable daughter isotope ratio?

Back 37

50:50 (The answer is true for the breakdown of all radioactive isotopes.)

Front 38

Precambrian

Back 38

all geologic time before the Phanerozoic eon (the current eon we live in)

Front 39

epochs

Back 39

a group of the geologic time scale, that is a subdivision group of a period

Front 40

a subdivision of eon is a what

Back 40

a era

Front 41

The Phanerozoic eon began how long ago

Back 41

542 million years ago

Front 42

what era do we live in

Back 42

cenozoic era

Front 43

Name the 4 types of eons

Back 43

Phanerozoic, Hadean, Proterozoic, and the archean eon

Front 44

the correct sequence from oldest to most recent or current eras within the phanerozoic eon on the Geologic Time Scale?

Back 44

Paleozoic, Mesozoic, Cenozoic

Front 45

Which eon translates to “visible life” from the Greek?

Back 45

Phanerozoic

Front 46

Which is the shortest interval of geologic time?

Back 46

epochs

Front 47

The subdivisions of the Geologic Time Scale were based on which criteria or characteristics?

Back 47

types of fossils within the units

Front 48

Which event is generally used to indicate the beginning of the Phanerozoic eon?

Back 48

widespread occurrence of hard parts

Front 49

Carbonization

Back 49

Fine sediment encases plant remains, leaving behind an organic residue

Front 50

A worm burrow is an example of which type of fossilization?

Back 50

Trace Fossil

Front 51

Lateral continuity (principle of)

Back 51

A principle which states that sedimentary beds originate as continuous layers that extend in all directions until they grade into a different type of sediment or thin out at the edge of a sedimentary basin.

Front 52

Geologic Time Scale

Back 52

The division of Earth history into blocks of time—eons, eras, periods, and epochs. The time scale was created using relative dating principles.

Front 53

Numerical Date

Back 53

The number of years that have passed since an event occurred.

Front 54

Who invented the principle of superposition

Back 54

Nicolas Steno, a Danish anatomist, geologist and priest

Front 55

Principle of original horizontality

Back 55

A principle by which layers of sediment are generally deposited in a horizontal or nearly horizontal position.

Front 56

If we observe rock layers that are flat it means what

Back 56

they have not been disturbed and still have their original horizonality

Front 57

Principle of lateral continuity

Back 57

A principle which states that sedimentary beds originate as continuous layers that extend in all directions until they grade into a different type of sediment or thin out at the edge of a sedimentary basin.

Front 58

correlation

Back 58

The process of establishing the equivalence of rocks of similar age in different areas.

Front 59

Principle of cross-cutting relationships

Back 59

states that geologic features that cut across rocks must form after the rocks they cut through

Front 60

Inclusions

Back 60

Fragments of one rock unit that have been enclosed within another

Front 61

xenoliths

Back 61

An inclusion of unmelted country rock in an igneous pluton.

Front 62

What is significance of an unconformity

Back 62

It represents a long period during which deposition ceased, and then erosion removed previously formed rocks, and then the deposition resumed

Front 63

The scientific study of fossils is called

Back 63

paleontology

Front 64

permineralization

Back 64

a process of fossilization in which mineral deposits form internal casts of organisms. Carried by water, these minerals fill the spaces within organic tissue

Front 65

Name 5 ways that an animal or a plant can be preserved as a Fossils

Back 65

Permineralization, Molds or casts, carbonization or impressions, amber, and trace fossils

Front 66

How is a mold created

Back 66

When a shell or other structure is buried in sediment and then dissolved by underground water a mold is formed

Front 67

carbonization

Back 67

It occurs when fine sediment encases the remains of an organism. As time passes pressure squeezes out the liquid and gaseous components and leaves behind a thin residue of carbon

Front 68

Amber

Back 68

the hardened resin of ancient trees which often contains fossilized insects

Front 69

What conditions favor the preservation of an organism of a fossil

Back 69

Ether rapid burial or the possession of hard parts

Front 70

List three examples of trace fossils

Back 70

Tracks, burrows, Coprolite (fossilized poo)

Front 71

What is the goal of correlation

Back 71

To develop a geologic time scale that is applicable to the entire earth

Front 72

Principle of fossil succession

Back 72

The definite and determinable order in which fossil organisms occur. Fossil succession enables us to identify many time periods of rocks by their fossil content. Therefore any time period can be recognized by its fossil content

Front 73

Index Fossils

Back 73

Fossils that are widespread geographically and are limited to a short span of geologic time. So their presence provides an important method of matching rocks of the same age

Front 74

Fossil assemblage

Back 74

The overlapping ranges of a group of fossils (assemblage) collected from a layer. By examining such an assemblage, the age of the sedimentary layer can be established.

Front 75

Other than being important time indicators how else are fossils useful to geologists

Back 75

Fossils are good environmental indicators; showing where the fossils once lived

Front 76

A neutron is actually a proton and an ________ combined

Back 76

electron

Front 77

uranium has how many isotopes

Back 77

three

Front 78

parent

Back 78

An unstable radioactive isotope

Front 79

daughter products

Back 79

The isotopes resulting from the decay of the parent

Front 80

earth's oldest rock

Back 80

4.28 billion years old

Front 81

Why is radiometric dating a reliable method for determining numerical dates

Back 81

because the rates of decay for many isotopes have been precisely measured and do no vary under the physical conditions that exist in Earth's outer layers

Front 82

radiocarbon dating

Back 82

Dating of events from the very recent geologic past (the past few tens of thousands of years) based on the fact that the radioactive isotope of carbon is produced continuously in the atmosphere.

Front 83

radiocarbon dating is only useful in dating

Back 83

organic materials such as wood, charcoal, bones, flesh, and cloth

Front 84

Name the basic structure of the geologic time scale from largest units of time to smallest

Back 84

Eons, Eras, Periods, and Epochs

Front 85

How many periods does the paleozoic era contain

Back 85

7 periods

Front 86

How many periods does the mesozoic era contain

Back 86

3 periods

Front 87

How many periods does the cenozoic era contain

Back 87

3 periods

Front 88

Epochs from later times are simply termed..

Back 88

Early, middle, and late

Front 89

The archean and proterozoic eons are often referred to as the

Back 89

Precambrian

Front 90

The earliest interval of earth history (eon); before the oldest known rocks

Back 90

Hadean (termed from the Greek god of the underworld, Hades)

Front 91

Why is -zoic part of so many names on the geologic time scale

Back 91

because -zoic stands for life

Front 92

How do geologist date sedimentary strata

Back 92

By examining their relationship to igneous rock

Front 93

Why it is often difficult to assign a reliable numerical date to a sample of sedimentary rock

Back 93

because radiometric dating often is useless to sedimentary rock so geologist have to rely on relative dating