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rowan study decks > geology final set > Flashcards

geology final set Flashcards

1
Q

uniformitarianism

A

-Uniform rates for geologic processes
-The observable processes on the planet have been going on at the same rates for a long time

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2
Q

relative dating

A

-Putting the events in order
-Relative dating is the process by which geologists put geologic events recorded in rocks into chronologic order.
-Note that relative dating does not put a discrete age measured in number of years on geologic events, it just puts the events in a order from first to last.

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3
Q

relative dating: superposition

A

Sedimentary rocks on bottom are old, ones on top are young

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4
Q

original horizontality

A

The law of original horizontality states that sedimentary rocks were deposited in horizontal layers. Thus, sedimentary layers that are no longer horizontal have been deformed and tilted by a deformational event that occurred after the rocks were deposited

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5
Q

cross-cutting relationships

A

The law of cross cutting relationships states that geologic rocks or features that cuts across other rocks or features must be record the younger event. For example, these basaltic dikes are younger than the sedimentary rocks they cut.

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6
Q

unconformities:

A

represents missing time in the rock record

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7
Q

implication of Uniformitarianism

A

One important implication of this idea is that catastrophic events like earthquakes and floods cannot explain the features that we see on our planet, and our planet has instead been shaped by currently observable, slow processes that have been active for millions to billions of years.

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8
Q

Angular unconformity

A

-Sedimentary rocks below the unconformity - these rocks are at an angle to the unconformity
-An angular unconformity in one in which the rocks below the erosional surface are tilted to non‐horizontal orientations, and suggest that erosion was associated with deformation.

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9
Q

Nonconformity

A

-Igneous or metamorphic rocks below the unconformity
A nonconformity is an unconformity in which the rocks below the surface are either igneous intrusive rocks or metamorphic rocks.
-Because these rocks only form inside the Earth, other pre‐exiting rocks above them must have been eroded away to expose the deeper rocks at the surface of the Earth where they were overlain by sediments.

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10
Q

Disconformity

A

-Flatline sedimentary rocks below the unconformity
-Recognizable by fossils or something that demonstrates these rocks are much much older than the younger rocks on top

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11
Q

Fossils

A

are formed when a plant or animal is buried in sediments. As the sediments become lithified, the remains of the plant or animal are preserved in the sediments as either imprints, or through replacement during the cementation phase of lithification.

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12
Q

faunal succession

A

-is the evolution of different plants and animals that can be observed in sedimentary rocks of different ages.
-More simple organisms are preserved in older sedimentary rocks at the base of the stratigraphy, and the fossils become more and more complex in stratigraphically higher, and younger sedimentary rocks.
-Disconformity: missing layers in the faunal succession

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13
Q

absolute dating:

A

-Putting an age on a rock or event
Based on radioactive decay
-Unstable parent isotope decays to stable daughter isotope
-Half life: time for ½ of parents to decay

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14
Q

Radioactive “clock”

A

-Starts “ticking” when the daughter atoms begin to accumulate rocks and minerals
-Starts “ticking” when the rock cools down
Good for igneous and metamorphic rocks

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15
Q

bracketing

A

-For sedimentary rocks
-Put a lower and upper age limit on the rock

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16
Q

The Hadean Period

A

-was from 4.5 to 4.0 Ga (billion years ago). The Earth was young and hot, and if there was life it probably very primitive and didn’t have much chance to evolve
-The conditions of the Earth were even hard for rocks. -The oldest mineral grains are as old as 4.4 billion years, but the oldest non‐ disputed rocks are ~4.0 billion years old, and attest to the fact that rocks in the Hadean were probably formed and then recycled/remelted before they could be preserved.
-NO ROCKS FROM HADEAN PERIOD

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17
Q

The Archean period

A

-First life evolves (simple)
-4.0-2.5Ga
-Continental crust forms
-The Archean Earth was much more inhabitable with water in the oceans
-Rocks that formed at this time are preserved in old portions of continental crust ‐ at this location in Greenland, there are at least three major rock-forming events that are recorded: 3.6 Ga (not pictured), 3.0 Ga, and 2.7 Ga
-Geologist debate how these early continental granitic rocks formed. Some geologists prefer a model for the formation of early continental crust that is similar to modern plate tectonics.

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18
Q

The Proterozoic Period

A

-(2.5 to 0.54 Ga)
-Note the lack of plants on the continents
-Plate tectonics
-During the Proterozoic, most geologists believe that plate tectonics was operating in much the same way as it does today.
-The Proterozoic is also characterized by the evolution of multicellular life. Importantly, there is evidence for the first organisms capable of photosynthesis during this time, and the Earth’s atmosphere become oxygenated.

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19
Q

The Phanerozoic Period

A

-The Phanerozoic Period (0.54 Ga to the present)
-During this time, complex life evolved, and eventually came to inhabit the oceans and land masses across the globe.
-three different eras: the Paleozoic, Mesozoic, and Cenozoic.
-The periods within the Phanerzoic are defined by fossil assemblages within sedimentary rocks. Although the number of genera/species has increased over time, the end of each period is marked by a mass extinction event associated with the change of fossil assemblages.

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20
Q

Phanerozoic period: The Paleozoic

A

-(540 Ma (million years ago) to 251)
-The beginning of this era was characterized by a rapid increase in biodiversity (mainly in oceanic enviroinments), and is commonly referred to as the ‘Cambrian explosion.

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21
Q

Phanerozoic eras: the Mesozoic

A

-(from 251‐65 Ma)
-plants and animals became common on land
includes the geologic periods Triassic, Jurassic, and cretaceous famous for dinosaurs!

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22
Q

Phanerozoic eras: The Cenozoic

A

-(from 66 Ma to the present)
-is associated with the rapid development of different species of mammals… including homo sapiens, which have only been present on Earth for the past ~200,000 years!

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23
Q

mass extinction 1: The end of the Cretaceous

A

-(when the dinosaurs went extinct)
- coincides with the impact of a giant meteor that impacted on the northern tip of the Yucatan Peninsula (Mexico).
-also coincides with a massive outpouring of volcanic rocks in India (called the Deccan Traps). These eruptions started ~2 million years before the dinosaurs went extinct

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24
Q

mass extinction 2: The end‐Permian Mass extinction (251 Ma),

A

when 81% of all marine species and 70% of all terrestrial vertebrates became extinct, is temporally associated with the eruption of the Siberian Traps- huge volcanic eruptions in Siberia

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25
Q

longitudinal profile

A

plots elevation on the y-axis and distance along the length of the river on the x-axis, and shows the slope of the different parts of the river. The headwaters generally have a steep slope, the floodplains have a gentle slope, and the delta is essentially flat.

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26
Q

The cross-sectional profile

A

is the topographic profile across the river. The cross-sectional profile of a river in the headwaters is ‘V’ shape, and is broad and flat in the floodplains

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27
Q

parts of river

A

Rivers have different parts, sometimes called reaches: the headwaters, floodplains, and delta.

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28
Q

headwaters

A

The headwaters generally have a steep slope
-The cross-sectional profile of a river in the headwaters is ‘V’ shape

29
Q

river stuff

A

-Slope, volume, and sinuosity
-The velocity of the water in the river is partly a function of slope: steeper slopes makes faster water
-velocity of the water also varies with the amount of water in the stream.
-When there is more water in the stream, the channel is deeper, there is less friction between the flowing water and the stream bed, and the water travels faster.
that is why water flows very fast during floods.
-sinuosity: degree/amount of meandering

30
Q

river stuff pt. 2

A

-Water velocity also varies as a function of the stream shape, and its position in the stream
-In general, water travels fast on the outside corner of a bend in the river (where the channel is deeper), and slower on the inside corner of the stream (where the water is shallow).

31
Q

discharge

A

is the amount of water flowing through the stream at any given moment and is measured in cubic meters per second. During floods, discharge is high.

32
Q

stream power

A

Stream power: Stream erosion vs. deposition
Stream power is the amount of energy that a stream has to do ‘work.’
Stream power = slope * discharge.
The work that streams have to do is:
1) move any sediment that is in the stream bed
2) if there is any leftover energy, erode the bedrock
if stream power is greater than critical stream power, the stream will erode the bedrock.

33
Q

critical stream power

A

Critical stream power is the amount of energy that is required to move sediment in the stream bed.
- if stream power is greater than critical stream power, the stream will erode the bedrock.

34
Q

sediment transport

A

-If stream power is less than critical stream power, not all of the sediment will move, and some sediment will be deposited.
-In general, higher slopes indicate higher stream power and lead to erosion whereas lower slopes indicate lower stream power, and is thus more likely to cause sediment deposition.

35
Q

headwaters

A

-In the headwaters, slopes are generally high, erosion is dominant, and V-shaped valleys get carved.
-Streams in the headwaters (and elsewhere) move larger clasts and grains along the bed (the bed load) and smaller grains and mud within the water column (the suspended load).
-Streams also move material that is dissolved in the water (the dissolved load).
-Suspended load: The bulk of a river’s sediment is moved during floods in the suspended load.
-Because streams and rivers in the headwaters have more stream power than critical stream power, the extra stream power is used to push sediment and erode the bedrock through abrasion.

36
Q

downcutting

A

Erosion by rivers: downcutting
Because streams can only erode through abrasion, the river will downcut through the bedrock only along the bed of the river, and river canyons tend to get deeper and deeper.
In areas where the rocks are unusually strong, this can carve spectacular slot canyons
but in most places, the rocks aren’t very strong, and the slot canyons collapse through landslides, and the classic V-shaped valley is formed.
V-shaped valley = downcutting + landslides

37
Q

floodplains

A

-In the floodplains, the stream has a lower slope, and is characterized by meandering (bending/curving/winding) rivers that move across broad, flat floodplains.

38
Q

floodplains: meandering

A

-Meanders form as the outside bend of river, where the water is travelling fast, gets eroded.
-This part of the river is called the cut bank.
-At the same time, along the inside bend of the river, the water velocity is slower, and sediment is deposited.
-This part of the river is called the point bar
-Meanders can get exaggerated, and eventually, a meander neck can get cutoff, and an oxbow lake is formed.
-Meandering streams slowly migrate across the floodplains as the cut banks and point bars evolve over 100s to 1000s of years, and rather than carving V-shaped valleys meandering streams cause side-to-side erosion.

39
Q

natural levees

A

form during when floods when fast-moving, sediment-rich water flows over the banks, slows down and deposits sediment along the banks of a river.

40
Q

Floodplain deposits

A

Floodplains can deposit sediment if, as the stream migrates across the floodplain, the floodplain is also subsiding (e.g., in a rift or flexural basin), so that when the stream migrates back through that area, a new layer of sediment is deposited over the previous layers.

41
Q

delta

A

-In the delta, the slope goes to zero because the river has transitioned to flat water. Because slope = 0, stream power = 0, and sediment is deposited.
-When one part of the delta becomes full of sediment, the stream starts to deposit sediment in a new area. I call this lobe-by-lobe deposition.
-Delta deposits are usually characterized by thick deposits of fine-grain sediment like mud and silt.

42
Q

mass movement influencing factors

A

-Influencing factors: bedrock conditions
Higher chance of mass movement event:
1. Steep slopes
2. Fractures in the rock
3. Water
Decrease chance of mass movement:
1. Vegetation

43
Q

type of movement

A

soil creep, slump, rock falls, debris flows

44
Q

soil creep

A

Relatively slow
Expansion and contraction - multiple slow cycles of freeze/thaw or wet/dry
Rotational effects for things on the surface (ex: fence post)

45
Q

slump

A

Happens more quickly
Ground slips along curved plain - material slumps down
Results in hummocky topography

46
Q

rock falls

A

When rocks fall
Happen frequently
Steep cliff where rocks fall at the same time
Hazardous

47
Q

debris flows

A

When all the material moving downhill at once become fluidized
Whole mixture of material starts to act as one single fluid
Result: runout goes much further than a rock fall

48
Q

coastal erosion

A

abrasion in tidal zone, a marine terrace

49
Q

abrasion in tidal zone

A

Undercut cliffs are called wave-cut notches. Repeated undercutting and collapse leads to the development of flat surfaces formed at the tide line that are called wave-cut benches

50
Q

marine terrace

A

is a wave-cut bench that has been uplifted (usually tectonically) above sea level. In this picture, the old wave-cut bench is covered in grass, while a new wave-cut bench gets carved.

51
Q

types of glaciers

A

-valley (or alpine) glaciers
accumulate in valleys and flow down the valley
-ice sheets
Ice sheets flow radially outward from a central area where the ice is thickest.

52
Q

accumulation zone

A

-Above the equilibrium line, the weather is cold enough that snow and ice stays frozen all year round.
-Thus, snow and ice accumulates in layers year after year.
-As snow gets buried, it goes through a series of transitions as the snow recrystallizes and air is forced out of the snow, and the snow transforms from fresh powder, to firn, and eventually ice at several hundred meters depth.
-Snow - firn - ice
-Once the snow and ice in the zone of accumulation becomes thick enough, it begins to flow downward under its own weight, and ice can eventually flow, and persist below the equilibrium line.
Essentially, ice from above the equilibrium line resupplies the ice below the equilibrium line fast than it can melt.
-Glacial ice typically moves downhill at rates of meters to 10s-of-meters per year.

53
Q

glacial movement

A

Ice can move downhill by sliding along its base as well as by flow.

54
Q

glacial movement: plastic flow

A

Flow can occur in through ductile (or plastic) processes in which the ice moves but doesn’t form fractures, and by brittle flow in which chunks of ice flow past each other along fractures

55
Q

glacial movement: brittle flow

A

Crevasses are fractures that form in the top of a glacier as its upper portions flow downhill brittlely.

56
Q

Ablation zone

A

-Below the equilibrium line, snow and ice melts in the summer months.
-Melting occurs as the ice comes into contact with warm air, is heated by the sun and is melted by water.
-Calving at the terminus of this glacier is forming icebergs!

57
Q

advance glaciers

A

An advancing glacier has a terminus (or toe) which moves downhill one year after the next.
Advancing glaciers have accumulation greater than ablation, so ice moves into the zone of ablation at a faster rate, and is able to reach farther downhill before it all melts.

58
Q

retreating glaciers

A

-has a terminus that is positioned uphill in successive years.
-Retreating glaciers are characterized by accumulation less than ablation, so the ice from the zone of accumulation does not flow downhill as far before it melts.
-In general, increasing temperatures causes the equilibrium line to move uphill, and thus the amount of accumulation decreases, and glacier retreat.
However, in areas where precipitation increases, glaciers can advance even as the temperature increases.

59
Q

basal slip

A

-Glaciers can move rapidly downhill during surge events that can occur periodically when water builds up beneath the surface of a glacier and greatly enhances the rates of basal slip.
-During surges, glacial ice can move downhill at 100s of meters to kms per year.

60
Q

glacial erosion processes

A

abrasion and plucking.
This abrasion-plucking pair forms roche moutonees: abrasion on the uphill side and plucking on the downhill side. Roch moutonees can be formed at the outcrop scale

61
Q

abrasion (glaciers)

A

Abrasion occurs when rocks that have been incorporated into the ice scour, scratch and polish the bedrock as they are dragged along the bottom of the glacier.
characterized by polished and relatively flat surface

62
Q

plucking

A

Plucking is a freeze/thaw process that happens at the base of the glacier as water flows into fractures, freezes and expands, and breaks rocks from bedrock.
steep, fractured surface associated with plucking

63
Q

glacial landscapes

A

In contrast to river valleys, glaciers form U-shaped valleys.
Valley glaciers commonly originally form in V-shaped river valleys as snow and ice accumulates in the high mountains.
The characteristic U shape forms as the accumulated ice flows downhill, and abrasion occurs along the base of the glacier as well as the valley walls wherever the ice flows (not just at the base like a river), and the ice itself prohibits landslides.
When the glacier retreats, the U-shaped valley remains.

64
Q

glacial landscapes: horn

A

a peak that is carved by valley glaciers moving away from a high point that remained free of ice.

65
Q

glacial landscapes: cirque

A

a depression that forms at the head of a glacier – this low point essentially forms on the uphill side of a valley-scale roche moutonee.

66
Q

pater noster lakes

A

series of lakes in glacial valleys that form as water pools in depressions created by multiple valley-scale roche moutonee’s.

67
Q

glacial deposits: morain

A

Glaciers carry boulders, rocks, sand, silt, and mud of all sizes together downhill.
When a glacier retreats, all the debris it carried is leaves a pile of debris called a moraine.
The unsorted sediment in a debris is called till
.Morains are easily differentiated from river sediment because it is unsorted rather than sorted by size as is the norm for deposits formed by moving water.

68
Q

greenhouse effect

A

-Greenhouse gasses are found naturally within the Earth’s atmosphere. Incoming solar radiation is strong enough to penetrate the atmosphere and warms the surface of the Earth.
-This warmed Earth surface radiates energy outward toward space. However, this energy is not strong enough to penetrate greenhouse gasses in the atmosphere. Instead, the greenhouse gasses are warmed, and radiate heat back toward Earth. The more greenhouse gasses in the atmosphere, the stronger this effect becomes.

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