GEOLOGY 101 EXAM #2

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Geologic Time Scale

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130 Terms

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Geologic Time Scale

A record of the geologic events and life forms in Earth's history.

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Nicholas Steno

father of stratigraphy

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Uniformitarianism

current geologic processes, occurring at the same rates observed today, in the same manner, account for all of Earth's geological features

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Stratigraphy/Stratification

study of rock layering: diagnostic for sedimentary rocks

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I. Principle of Original Horizontality

layers of sediment that are generally deposited in a horizontal or nearly horizontal position -PART OF STRATIGRAPHIC SUCCESSION

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II. Principle of Superposition

younger items are closer to the surface of the earth than older items -PART OF STRATIGRAPHIC SUCCESSION

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Stratigraphic Succession

a chronologically ordered set of rock strata (strata = a layer or a series of layers of rock in the ground)

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III. Cross-cutting Relationships

principle stating that a fault or intrusion is younger than the rock it cuts across.

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IV. Role of Fossils

shows organisms that populated Earth at that time rock layers formed

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Disconformity

exists where part of a sequence of parallel rock layers is missing; most common type of unconformity -between SEDIMENTARY rx layers

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Nonconformity

Sedimentary strata overlay metamorphic or igneous rocks -between SEDIMENTARY & IGNEOUS rx layers

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Angular Uncomformity

layer of rock tilted, eroded, and weathered, then second period of sediment deposition occurred on top of the tilted layer -NOT PARALLEL

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Block Diagram

know what layers came first/second, etc.

<p>know what layers came first/second, etc.</p>
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Formation

series of rock layers that have the same physical properties + same fossils; gives period of geologic time

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Radiometric Dating

method used to determine the age of rocks using the rate of decay of radioactive isotopes -can give precisely when rocks formed

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Radioactive Decay

spontaneous process in which an isotope (the parent) loses particles from its nucleus to form an isotope of a new element (the daughter)

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Half Life (T½)

time required for one half of the original number to decay

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Half life of Potassium-40 (K-40)?

1.3 billions years -daughter = Argon (Ar-40)

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Half life of Rubidium-87 (Rb-987)?

47 billion years -daughter = Strontium-87 (Sr-87)

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Half life of Carbon-14 (C-14)?

5,730 years -daughter = Nitrogen-14 (N-14)

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What is the importance of Geologic Time?

system of chronological dating that relates geological strata (stratigraphy) to time -used by Earth scientists to describe the timing and relationships of events that have occurred

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Precambrian

formation of Earth (4.5 billion years ago) to first sign of complex life (540 million years ago) -origin > one celled organism > multi-celled organisms

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Paleozoic

544 to 245 million years ago -breakup of super continent (Pangea!) -plants -first land vertebrates

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Mesozoic

252 million years ago to about 66 million years ago

  • life diversified rapidly -DINOSAURS, BITCHES. DINOSAURS!!!

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Cenozoic

65 million years ago to the present -extinction of dinosaurs :( -Age of Mammals

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Mass Wasting

downhill movement of geological materials due to gravity

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Angle of repose

maximum angle at which a slope of loose material will lie without cascading down -differs if wet vs dry -differs if sand or clay

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Rock falls

rapid, rock leaves surface -fastest mass movement

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Rock slides

rapid, rx fall over 100 miles an hour, rx still on surface (frictionless but still connected to land surface) -slower than rock fall, faster than landslide

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mudflows

heavy precipitation liquefies ground soil -slower than landslide, faster than slump

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landslides

rock slide but with soil and rock -slower than rock slide, faster than mudflow

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earthflows

mudflows but with soil and regolith

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slumps

pieces of a hill slide down and form a depression -scarp above and bulge underneath -slower than mud + earth flows, but faster than hill creep

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hill creep

the very slow to almost unobserved movement of materials down a slope (measured at fraction of inch) -apparent on all hills, seen from trees -slowest mass waste

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falls

dominantly vertical downward movement -move as separate blocks -free-fall

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subsides

-collapse into void -dominantly vertical downward movement -move as separate blocks

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flows

-flow over landscape -move as very viscous fluids -turbulence within moving mass

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slides

-slide on top of basal slip surface -move as semisolid mass -some preslide coherence maintained withing moving mass

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How are rock slides similar to mudslides?

  1. Need a valley

  2. stratified rocks

  3. abundant water, precipitation

  4. triggering mechanism, ex. earthquake

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shear strength

forces resisting movement down, includes frictional resistance and cohesion among the particles that make up the object.

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shear force

pushing the block down the slope, acts against NORMAL FORCE, which tries to push the block into the slope

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How can slopes become stable?

cementing, absorption, cohesion

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How can slopes become unstable?

fractures, weathering, bedding,

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Supports against mass waste

rock bolts, concrete buttress, shotcrete facing, metal straps + bolts, cable lashing

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crystalline rock strength

strong -Ex. granite, basalt, gneiss

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metamorphic rock strength

moderately strong -Ex. schist

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sedimentary rock strength

variable strength -Ex. dolostone + limestone = strong -Ex. sandstone + conglomerate = moderately strong -Ex. mudstone = weak

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streams

major geological agents operating on land surface -velocity is not constant -at bottom v = 0

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When does velocity increase in a stream?

towards the center and the surface

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tributaries

river or stream flowing into a larger river or lake

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discharge

total volume of water flowing past a point in given time period

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D = v * a

calculates discharge; D= discharge A= area V= volume

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When does discharge and velocity increase?

downstream with increasing water from tributaries

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capacity

the total amount of sediment that a stream can carry -increases with discharge -HOW MUCH?

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competence

size of a particle a stream can carry -increases with discharge -HOW BIG?

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solution

form of stream transport; dissolved materials in water, i.e., iron oxide or CaCO3 -makes hard water

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suspension

form of stream transport; small grains suspended down the length of river/stream -usually clay and silt particles -solid particles

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saltation

form of stream transport; materials move by sudden jumps -Saltando (spanish word for jumping)

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bed load transport

form of stream transport; pushing and rolling along the bottom, never rising up into fluid

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channel

flowing water part

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floodplain

relatively level area surrounding channel within valley -WHERE RIVER MEANDERS

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point bar

low, curved ridge of sand and gravel along the inner bank of a meandering stream -form through the slow accumulation of sediment deposited where velocity drops

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cutbank

nearly vertical cliff produced by erosion of the banks of a stream

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oxbow lakes

crescent-shaped lake formed when a meander of a river or stream is cut off from the main channel.

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natural levee

deposit of sand or mud built up along, and sloping away from, either side of the flood plain of a river or stream

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drainage basin

area of land that river and tributaries drain

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grades bed

fine = point bar coarse = delta

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How does sediment keep pace with sinking of land surface?

land near rivers is frequently supplied with sediment -builds land upward

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River profiles

Potential vs Kinetic; -high kinetic = fast -low kinetic = slow -high potential = higher -low potential = lower

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base level

elevation of a standing body of water which the stream flows

  • locally; streams, lakes, dams

  • universally; the ocean

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Where do floods occur usually?

River floodplains and coastal areas -sometimes with unusually high rainfall

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Recurrence interval (100 year flood)

the height to which a river will rise every 100 years

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50 year flood

estimated probability of a flood event happening every 50 years

  • probability = 2%

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Dams

traps water to create reservoir

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Why do dams suck?

traps sand from rivers, sediment accumulates behind damn and never reaches beaches, become useless, DESTROYS WILDLIFE

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Why are dams used?

suppress floods, provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability, hydropower

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Groundwater

water found underground in the cracks and spaces in soil, sand and rock

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How does groundwater flow?

transported through aquifers because of two main reasons: GRAVITY + PRESSURE

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Uses of groundwater

drinking water, food growing, industrial processes, recharge for streams and lakes

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Porosity

total void space within rock

  • volume of void space / rock volume = porosity %

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Permeability

interconnected-ness of all pore spaces

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Examples of Rocks with Permeability + Porosity

GRAVEL: high porosity; high permeability. SAND: high porosity; medium permeability. MUD: high porosity; low permeability. GRANITE: very low porosity; very low permeability. FRACTURED GRANITE: low porosity: very high permeability.

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Best rock for groundwater use?

gravel

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What does groundwater mimic?

the topography of the land

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Is groundwater slower or faster than surface water?

slower

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Contamination of groundwater

occurs when man-made products such as gasoline, oil, road salts and chemicals get into the groundwater and cause it to become unsafe and unfit for human use

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Wind

atmospheric motion driven by temperature gradient from equator to poles

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Air movement

high to low pressure, a lot more complicated though

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What causes wind belts?

uneven solar heating at equator + Coriolis effect

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Coriolis effect

deflects to the eat in N. Hemisphere, strong at equator, weakest at poles

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Which direction does air turn in the Northern Hemisphere? Southern Hemisphere?

right = north left = south

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atmospheric circulation cells

large circuit of air

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Hadley cells

tropical cells found on each side of the equator

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trade winds

a wind blowing steadily toward the equator from the northeast in the northern hemisphere, southeast in the southern hemisphere

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ferrel cells

found at mid latitudes

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westerlies

belt of prevailing westerly winds in the mid-latitudes of the northern and southern hemispheres

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polar cells

found near the pols

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polar easterlies

cold, dry prevailing winds that blow away from high-pressure areas of the poles

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doldrums

calm equatorial areas where two Hadley cells converge (L)

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Horse latitudes

areas between Hadley and Ferrel cells; little surface wind

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