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Geology II > Exam One > Flashcards

Exam One Flashcards

1
Q

What are the three rock types?

A
  1. Sedimentary
  2. Metamorphic
  3. Igneous
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2
Q

How are sedimentary rocks formed?

A

Formed from deposits of pre-existing rock (weathering, erosion, deposition)

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3
Q

How are metamorphic rocks formed?

A

when rocks are subjected to high heat and high pressure

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4
Q

How are igneous rocks formed?

A

Melting, magma cools and then crystallizes

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5
Q

Which type of rock forms at the Earth’s surface?

A
  • Sedimentary rocks
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6
Q

How do sedimentary rocks tell us about life and the environment when and where they formed?

A
  1. Grain Size: tells us how close/far the rock is from its origin.
  2. Grain Shape: tells us about the mode of transportation.
  3. Structures tell us about the environment it formed in (ripple marks, graded bedding, etc.)
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7
Q

Why do we study the history of Earth?

A

Teaches us about past life and environments

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8
Q

loose grains or crystals (broken pieces of older rocks; ex: sand); weathered pieces of rock and other materials

A

sediment

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9
Q

grains or crystals held together. (ex: sandstone); when sediments are compacted and cemented together

A

sedimentary rocks

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10
Q

What are the four steps of the sedimentary cycle?

A
  1. Weathering
  2. Erosion
  3. Transport
  4. Deposition
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11
Q

break-down of older rocks into sediment; how sediment gets created (can happen anywhere rocks are on the surface of the Earth)

A

weathering

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12
Q

when the sediment created by weathering starts moving; removed from where it formed

A

erosion

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13
Q

the movement of sediment from one place to another (sediment in motion

A

transport

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14
Q

What are the four main ways a sediment is transported?

A
  1. Wind
  2. Water
  3. Gravity
  4. Ice
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15
Q

when the sediment stops moving; what allows it to potentially become a sedimentary rock in the future

A

deposition

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16
Q

Larger sand grains stop where water (speeds up/slows down)

A

slows down

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17
Q

What kinds of sediment are produced by weathering?

A

Clastic sediments (gravel, sand, silt, and clay)

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18
Q

how sediments change during transport

A

sediment maturity

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19
Q

A mature sediment is (poorly/well) sorted and (poorly/well) rounded

A

well-sorted and well-rounded

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20
Q

What are the three things taken into account when determining a sediments maturity?

A
  1. Grain size
  2. Grain shape
  3. Composition
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21
Q

How can grain size tell us how far sediment has traveled?

A

Large= hasn’t traveled far
Small= has traveled far

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22
Q

How can the shape of grains tell us how far sediment has traveled?

A

Angular= hasn’t traveled far
Rounded= has traveled far

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23
Q

How can the mineral composition tell us how far sediment has traveled?

A

The farther a sediment has traveled, the fewer kinds of minerals are left (losing the ones that can’t survive transport; more minerals near the source)

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24
Q

Most common mineral on Earth’s surface:

A

olivine

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25
Q

Most common mineral in Earth’s crust:

A

feldspar

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26
Q

One of the toughest minerals at Earth’s surface:

A

quartz

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27
Q

What clues tell us that a sediment was deposited in a continental (land) environment and not in the ocean?

A
  1. Color: red signifies a dry environment, a dark color indicates it formed in the ocean
  2. Roundness (sediment maturity): more angular on land and rounded in ocean
  3. Fossils: can tell us if animal lived on land or in ocean
  4. Sedimentary structures (river channels, sand dunes)
28
Q

What are 5 examples of continental depositional environments?

A
  1. Desert
  2. River
  3. Freshwater
  4. Glacier
  5. Lake
29
Q

What does sediment color tell us about depositional environments?

A
  • Red= sediment formed in hot or dry environment
  • Dark= sediment formed in a wet environment (ex: swamps → where coal forms from dead plants)
30
Q

Immature sediments are ________. (Either continental, marine, or transitional)

A

continental

31
Q

How can we tell that a sediment was deposited in a desert?

A

Often is a red color and often has cross bedding.

32
Q

Sand dunes are created by transport of ______. It cannot move heavy things like water can, so it moves things like sand.

A

wind

33
Q

Which part of a river can move heavier sediments?
- Deeper, faster moving water
- Shallow, slower moving water

A

Deeper, faster moving water

34
Q

how can we tell that a sediment was deposited in a river?

A
  • grey/green color
  • often poorly sorted
35
Q

Why are beach sands usually only made up of quartz? What happened to the other minerals as the sediments traveled from rivers to the coast?

A
  • quartz is resistant to both physical and chemical weathering
  • a long journey allows weaker minerals to be broken down
36
Q

Symmetrical ripples form from what? What does this tell you about its depositional environment?

A
  • back-and-forth waves (equal slopes) - tells you the sedimentary rock was deposited at the beach
37
Q

What sediment is most likely to end up far out in the ocean/offshore? Why?

A

Clay because it’s the smallest grain size so it can travel farther.

38
Q

What rock type is found offshore?

A

Shale (made up of clay); carbonaceous sedimentary rocks

39
Q

What type of rock forms from coral reefs?

A

Limestone (made from calcite shells)

40
Q

What can limestone tell us about the environment of the area it was formed in?

A

Coral reefs need clear, warm, tropical water far from shore or major rivers.

41
Q

Grain size (increases/decreases) away from the shore.

A

decreases

42
Q

Theory that states that rocks formed from sudden global disasters, not slow sediment deposition.

A

Catastrophism

43
Q

Did the theory of catastrophism say the Earth was very young or very old?

A

very young

44
Q

theory that states that ancient rocks formed the same way as modern ones

A

uniformitarianism

45
Q

Did the theory of uniformitarianism say the Earth was very young or very old?

A

very old

46
Q

Why did early uniformitarians like Hutton interpret that the Earth was very old?

A

Because the sediment cycle takes a long time. He stated that the processes of erosion, deposition, sedimentation, and upthrusting were cyclical and must have been repeated many times in the Earth’s history.

47
Q

What is the order of the periods in the Geologic Time Scale?

A
  1. Cambrian
  2. Ordovician
  3. Silurian
  4. Devonian
  5. Mississippian
  6. Pennsylvanian
  7. Permian
  8. Triassic
  9. Jurassic
  10. Cretaceous
  11. Paleogene
  12. Neogene
  13. Quaternary
48
Q

Today’s geologists are mostly uniformitarians, but they allow for exceptions… What are two examples of exceptions?

A
  1. Komatiite- igneous rock formed nowhere on earth today
  2. Tektites- debris from asteroid impact
49
Q
  • order of events
  • benefits: easy to figure out, helps test cause and effect
  • downside: doesn’t give us exact time, not precise
A

relative dating

50
Q
  • numbers, often years before the present
  • Benefits: can say how fast things happened and how often
  • Downside: difficult, expensive, not always possible
A

absolute dating

51
Q

the study of rock layers

A

stratigraphy

52
Q

What does the law of superposition state about the age of rocks and the order in which they formed?

A

younger rocks form on top of older rocks

53
Q

What does the principle of original horizontality tell us about how sedimentary rocks form?

A

Rock layers (sedimentary rocks) originally form horizontally bc of gravity; all tilting occurs later once the sediment solidifies and becomes rock

54
Q

igneous intrusions and faults cut through older rocks, therefore are younger.

A

Rule of Cross Cutting Relationships

55
Q

Cross-cutting relationships: If rock A is cross-cut by rock B, which one is younger? Which one is older?

A

Rock A: older
Rock B: younger

56
Q

What is an unconformity and why does it form?

A
  • missing rock layers due to erosion
  • why: older rocks were weathered and eroded before new rocks were deposited on top.
57
Q

Why are fossils used to compare the ages of rock layers?

A

Different fossil species lived at different times; layers with the same fossil species are about the same age.

58
Q

matching rock layers from one place to another

A

correlation

59
Q

What are index fossils?

A

Good fossils for matching rock ages

60
Q

3 Features that make a fossil an index fossil:

A
  1. Abundant and found all over the world
  2. Common/easy to find
  3. Existed for a short time/changed rapidly
61
Q

Two atoms with the same number of protons are the same

A

chemical element

62
Q

Different forms of the same element, which have the same number of protons but a different number of neutrons

A

isotope

63
Q

What does it mean for an isotope to be radioactive?

A

Their nuclei are unstable (because of the number of neutrons) and break down at a constant rate over time

64
Q

How can the rate of decay of radioactive isotopes help us date rocks?

A
  • Scientists can find out how old the rock is depending on the radioactive isotopes half-life.
  • Crystals only form with parent isotopes.
  • Daughter isotope that forms later is trapped in the crystal.
65
Q

In radioactive decay, a parent isotope changes into the daughter isotope of (the same/a different) element. Therefore, there is always a change in the number of (neutrons/protons)

A
  • a different
  • protons
66
Q

the time it takes half the parent isotope in a sample to decay into daughter isotope.

A

half-life

67
Q

Sedimentary rocks are dated by (absolute age/relative age) compared to igneous rocks.

A

relative age

Geology II (13 decks)

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