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Geo 101 > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

Why is weathering important?

A

Sedimentary rock makes up 75% of land surface
Provides soil for food and forests
It sculpts and modifies the Earth’s surface- it is responsible for all our landscapes

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2
Q

What is weathering and erosion, how do they differ?

A

Weathering: the process by which rocks are broken down at the surface
Erosion: the process that moves pieces of rock and deposits them elsewhere (wind, water, ice, and gravity are the agents of erosion)

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3
Q

What are the different types of chemical weathering?

A

Chemical: converts minerals and rocks into altered solids, solution, and precipitates- only occurs when those minerals are exposed to the weather
Hydrolysis: reaction of any substance with water (gains water and forms compound) ex: when Feldspar forms clay
Oxidation: a mineral reacts with oxygen to make a different product ex: Iron in minerals (like Pyroxene) forms Hematite (rust)
Dissolution: minerals dissolved by water or acid ex: halite, calcite

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4
Q

What are the different types of physical weathering?

A

Physical: fractures rock; breaks material into smaller pieces
Frost wedging, root wedging, exfoliation (sheeting/pressure release on Half Dome, Yosemite- found on intrusive rock)

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5
Q

What factors control the rate of weathering?

A

Rock properties (hardness, composition)
Climate (high temp breaks down faster)
Soil and vegetation (moisture and more vegetation will increase rate of weathering)
Length of exposure

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6
Q

How does the composition of the rock (the minerals it is composed of) affect weathering?

A

Felsic are more stable; will take longer to break down; because they are low temp.

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7
Q

How does the climate affect the development of the soil profile? Where would you find the least developed soils? Which one would you find the thickest accumulation of organic matter?

A

Climate (temp and precipitation): higher temperatures and more rainfall means more weathering and thinner soils
Time: longer time= thicker soil
Plants/Animals- organic matter
Slope- if too steep, little/no soil due to increased erosion

Soils from MOST to LEAST developed: Temperate, Rainforest, Desert, Tundra

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8
Q

Describe the soil profile

A

Organic rich at surface, enriched in clay and insoluble materials because soluble material leached.
Little organic material and soluble materials accumulates.
Slightly altered bedrock, broken and mixed with clay from chemical weathering.

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9
Q

What is sediment and where does it come from?

A

Sediment is material that is broken down from material that has been through weathering and erosion

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10
Q

What are the 3 classes of sedimentary rock and under what conditions do they form?

A

Clastic (composed of pre-existing rocks)
Biochemical (comprised of remains of plants and animals)
Chemical (composed of minerals precipitated out of solution like salt from evaporating seawater)

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11
Q

What is the most abundant sedimentary rock type group?

A

Siltstone, mudstone and shale make up 75% of sedimentary rocks

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12
Q

For clastic rocks be able to recognize sorting and rounding differences

A

If particles are about the same size, they are well sorted. If they are not the same size then they aren’t well sorted.

The more angular grains are, the less the transport. The more rounded the greater the transport.

With more transport, the particles become smaller and better sorted (similar in size)

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13
Q

How is the sorting, rounding and size of particles affected by the type of transport?

A

Wind: most selective agent, results in well sorted sediments (sand, silt, or dust)

Water: selection and sorting vary, depends on strength of currents (faster moving waves on a beach can move gravels, deeper, grain size decreases)

Glacial ice: not selective, results in poorly sorted sediments

Gravity: least selective, results in poorly sorted angular sediments (angular)

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14
Q

What does the energy level of a river indicate about the maximum particle size that can be transported?

A

The larger the particle size, the higher energy the river needs to be

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15
Q

What are sedimentary structures and what kind of information do they provide?

A

Bedding (stratification) parallel layers of sediments and each layer is called a bed

Cross-bedding: sets of bedded sediments at an angle to horizontal, deposited by currents ex: dunes

Graded bedding: beds progress from coarse grains at bottom to fine grains at top of bed, indicates waning of current

Ripple marks:
Mudcracks (Polygonal pattern of cracks that develop in mud as it dries)
Bioturbation (Burrow marks left in sediments by animals)
Tracks and trails

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16
Q

Be familiar with different kinds of sedimentary environments and what environments certain minerals would form in

A

Continental (clastic): streams (fluvial), desert, lake, glacial
Shoreline (clastic/chemical/biochemical): deltaic (where rivers enter the ocean), tidal flat (exposed at low tide), beach
Marine (mostly clastic with some chemical and biochemical): continental shelf, continental margin, reefs, deep sea

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17
Q

How are sedimentary rocks made?

A

The chemical and physical changes that transform sediment into rock.

As sediments accumulate, older layers become buried.
Sediments become compacted and heated.
Sedimentary rocks generally form up to about 10km deep

Lithification- hardening of soft sediments into rock (compaction and cementation)

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18
Q

Where does the heat and pressure come from to create metamorphic rocks?

A

Deep within the lithosphere

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19
Q

What are the factors controlling metamorphism?

A

Temperature- as temp increases minerals convert to new higher temperature minerals. (Diffusion: the movement of atoms due to thermal energy which forms new minerals)

Pressure

Fluids- released during recrystallization. Speed or reaction rates. Deposit or remove certain elements which can lead to formation of ore deposits.

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20
Q

Define recrystallization

A

crystals can grow larger or change shape

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21
Q

How does pressure affect metamorphic rocks?

A

Pressure:

Confining pressure: general pressure applied equally in all directions

Directed pressure: differential stress, unequal pressure, greater in one direction (the minerals grains will become aligned when acted on by directed pressure)

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22
Q

Define Foliation

A

the parallel alignment of minerals and/or surfaces

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23
Q

What are the two classifications of metamorphic rock?

A

Foliated- need to describe the following:

  • nature of foliation
  • size of crystals
  • the degree to which minerals are segregated in different minerals bands

Non-foliated

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24
Q

What is mineral grade

A

the degree to which a rock has changed from the parent rock of protolith

25
Q

What is retrograde path

A

Refers to the temp and pressure path of a metamorphic rock during its journey back to the surface

26
Q

What is contact metamorphism?

A

Heat from rising igneous intrusions metamorphose existing rocks

  • Low-High temp
  • Low pressures

Hot spots, convergent

27
Q

What is regional metamorphism?

A

Most common form of metamorphism. Mountain building.

Metamorphism caused by deep burial or tectonic forces that increase temp. and pressure over broad regions.

  • Low-High temp
  • Low-High pressure

Convergent

28
Q

What is hydrothermal metamorphism?

A

Hot water percolates through spaces in rocks

  • High temp
  • Low pressure

Divergent

29
Q

What is burial metamorphism?

A

Rocks are metamorphosed by the weight of overlying rocks

  • Low temps
  • Low pressures

Plate interiors

30
Q

What is impact/shock metamorphism?

A

Meteorite impact

-extremely high temp and pressures

31
Q

What is absolute dating vs relative dating?

A

Absolute: determining the actual time of

Relative: trying to put rocks in correct order of age without really knowing how old they are

32
Q

What is stratigraphy?

A

The description, correlation, and classification of strata in sedimentary rocks

33
Q

What is the principle of relative dating?

A

Whatever materials are deposited are deposited horizontally

34
Q

What is the exception to the principle of dating?

A

Cross bedding- when the current has changed direction

35
Q

What is the principle of superposition

A

In an undisturbed sequence of rocks, each layer is younger than the one beneath it and older than the one above it

36
Q

What is faunal succession?

A

Fossils as timepieces. Use of index fossils to correlate rocks from different locations.

37
Q

What are unconformities? What are the different types?

A

Markers of missing time (deposition of rocks isn’t continuous forever)

Disconformity
Angular
Nonconformity- sedimentary rocks in contact with crystalline igneous or metamorphic rocks (dissimilar rock types on contact with each other)

38
Q

What is the principle of cross cutting relations?

A

Whenever an igneous intrusion that cuts across layers occurs, the igneous intrusion is younger than the layers themselves. (Burger and toothpick example)

39
Q

What is the principle of inclusions?

A

Inclusions: preexisting rocks inside other rock

Inclusions are older than the rock itself

40
Q

What is radiometric dating?

A

uses unstable radioactive isotopes to determine absolute age.

the radioactive isotope, the parent isotope, evolves into a decay product, the daughter isotope, at a certain rate.

41
Q

What is the half life of an element?

A

the time it rakes for half of the parent to decay into its daughter product.

42
Q

What kinds of rocks can be dated with radioactive methods?

A

Igneous (really well)
-the clock begins when the molten rocks cool, dates age of crystallization
Sedimentary (fairly well)
Metamorphic (not well)

43
Q

What is carbon 14?

A

If carbon 12 is carried to the upper atmosphere, high energy protons from the sun will damage it, creating carbon 14

Organisms are made out of carbon, so they will consume the carbon 14.
The carbon 14 is radioactive and decays to nitrogen 14. What is the problem here?

We measure the amount of carbon 14 left in the material and compare it to the amount originally found in the atmosphere to determine the age

44
Q

Why dont we use carbon 14 dating on rocks:

A
  1. Most rocks do not contain carbon

2. The half life is only 5730 years, so you can not date anything older than about 70,000 years

45
Q

What is the geologic time scale?

A

Can be thought of as a relative-age calendar of the Earths geologic history.

46
Q

What is petrified wood?

A

Plant cells have been replaced by quartz

47
Q

What are trace fossils?

A

Evidence that the organism was there although the organism is gone.

Ex: leaf fossils, footprints

48
Q

What are index fossils?

A

Unique and easy to identify
Lived for a short period of time
Widely distributed around the world

49
Q

What are the two eons?

A

Phanerozoic- last 543 million years divided into three eras: cenozoic, mesozoic, paleozoic

Precambrian- from birth of Earth up to before complex life forms developed

50
Q

What is the first hint of life on Earth?

A

Comes from banded iron formations deposited in water

3.5 billion years old

51
Q

What are stromatolites?

A

Stump sized colonies of cyanobacteria. Only ones alive today are found in Australia.

52
Q

What is the Mesozoic era?

A

Dinosaurs first arrive

53
Q

What is structural geology?

A

Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories.

54
Q

What is the difference between stress and strain in rocks and what kinds are there?

A

Stress: force acting on the rock
Strain: a change in shape or size resulting from applied forces

55
Q

What kinds of stress are there and what boundary do they happen at?

A

Compression: where rocks are compressed or pushed together (convergent boundaries)

Tension: where rocks are pulled apart, away from one another (divergent boundaries)

Shear: rocks shift past one another in a horizontal motion (transform boundaries)

56
Q

What are the different kinds of strain?

A

Elastic formation: temporary strain, goes back to original form when stress is released

Brittle failure: permanent strain, cracks or fractures (faults)

Plastic deformation: permanent strain, flows and bends (folds)

57
Q

What is a strike-slip fault?

A

Side to side motion (horizontal)

Result of shear stress.

58
Q

What is a dip slip fault?

A

Motion is up down (vertical) along the fault plane. Cause by compression or tension.

Geo 101 (6 decks)

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