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Earth History Midterm #2 > Relative Age Dating > Flashcards

Relative Age Dating Flashcards

1
Q

How is geologic time recorded? Hint: GEO

A

Recorded by rocks, every layer records the period of time during which it formed

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2
Q

What are rock layers like?

A

Pages in a book since there is a chronological order, a start and finish

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3
Q

What are the two different ways to determine a rock’s age?

A

Relative age dating and Absolute age dating

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4
Q

What is relative age dating?

A

Age in relation to another thing, a sequence of events

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5
Q

What is absolute age dating?

A

A Specific numerical age

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6
Q

What did Aristotle believe about fossils?

A

He never realized that fossils were once living, “A great many fishes live in the earth motionless and are found when excavations are made”

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7
Q

What did Nicholas Steno do?

A

He was the founder of stratigraphy, the study of rock layers and layering, realized fossils were once living

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8
Q

What did many believe before Nicholas Steno’s findings?

A

Rocks that were formerly termed “Tongue stones” were actually shark teeth, Steno realized tongue stones were shark teeth

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9
Q

What are the 4 principles of stratigraphy that affect the relative age dating of rocks?

A

Each must be accounted for in age dating

1)Superposition
2)Original Horizontality
3)Cross Cutting
4)Inclusions

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10
Q

Steno’s principles of stratigraphy are concerned with determining an order of events. T/F

A

True

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11
Q

What is the principle of superposition?

A

It states that each rock layer is younger than the one below it

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12
Q

How do sedimentary rocks form when they become layers?

A

They are originally flat-lying layers, the oldest at the bottom and the youngest at the top

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13
Q

What does the principle of original horizontality state?

A

Sedimentary rocks are originally flat layers, if they are slanted/inclined then something must have happened to them

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14
Q

What can cause the folding of layers to cause them to not be flat-lying?

A

The squeezing along plate boundaries can change this, resulting in the folding of layers

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15
Q

What does the principle of cross-cutting state?

A

Younger features of the rock cut across older features

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16
Q

What does the principle of inclusion state?

A

Inclusions of another rock type must have come from an older rock body

Rock pieces INSIDE another rock is OLDER

17
Q

What are the 5 fundamental geological events that affect the relative age dating of rocks?

A

1) Deposition
2) Erosion
3) Intrusion
4) Faulting
5) Deformation

18
Q

What is intrusion?

A

Refers to the injection of magma into previously deposited sedimentary rocks, cross-cutting relationships govern their age

MAGMA INTRUDES ON EXISTING ROCK LAYERS

19
Q

What can magma do when it intrudes upon rocks?

A

It can either be sills or dikes

20
Q

What is a sill?

A

Magma intrusions that are PARALLEL to the layering

21
Q

What is a dike?

A

Magma intrusions that are CUTTING ACROSS layers

22
Q

What is faulting?

A

Refers to the breaking and offset of previously deposited sedimentary rock layers

23
Q

How are faults and fractures different?

A

Fractures show no visible offset, while faults do

24
Q

What is deformation?

A

Refers to any sort of tilting, folding, or rotation of sedimentary rock layers, deformed layers are no longer horizontal

25
Q

What are unconformities?

A

Represents a long period of time for which no rock is preserved, erosion removes previously formed rocks

Doesn’t have to be erosion, it can be a hiatus

26
Q

What are the 3 basic types of uncomformities?

A

Nonconformity: SEDIMENT OVER IGNEOUS OR METAMORPHIC

Angular Conformity: SEDIMENTARY OVER SEDIMENTARY BUT AT DIFF ANGLES

Disconformity: SEDIMENTARY OVER SEDIMENTARY, PARALLEL, BUT TIME MISSING

27
Q

How do nonconformities form?

A

Deposition of sediments on top of older igneous or metamorphic rock

28
Q

How does angular unconformities form?

A

Formed when flat layers are folded, eroded, and new sediment is deposited on top

29
Q

How do disconformities occur?

A

When erosion has removed previously deposited layers, leaving a gap in time

30
Q

What type of unconformities does the Grand Canyon have?

A

ALL 3

31
Q

What unconformity exists between the Tapeats Sandstone and the Underlying Vishnu Schist?

A

Nonconformity

32
Q

The Tapeats Sandstone still represents the same unconformity even though one is angular and one is non conformity. T/F

A

TRUE

Earth History Midterm #2 (7 decks)

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