Lecture notes start on page 143 Plate Tectonics and Geocycles are one lecture in two parts

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Lecture notes start on page 143 Plate
Tectonics and Geocycles are one lecture in two
parts
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The 4 Big Ideas in Geology

• The Rock Cycle (Fridays lecture)
• By the mid-1700s
• Antiquity of Earth - Deep Time (Fr. Stangs W
  11/11 Lecture)
• By the early 1800s, millions of years
• Faunal Succession (Fossil Record Core 6)
• By mid-1800s
• Plate Tectonics
• By late 1960s

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The Big Ideas ? Earth is Old and Dynamic

• Rather than Young and Static

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Recall The Scientific Method

• Observations
• Hypothesis (a testable explanation)
• Includes testing by prediction
• More observations (testing)
• Eventually -----gt Theory
• Not a hunch nor a fact, but the best
  available explanation using natural causes

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Plate Tectonics

• is a great example of discovery-driven science
  that was eventually supported by many
  hypothesis-driven predictions

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A sequence of observations about Earth throughout
human history
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The Ancient Greeks

• Knew that Earth was round (not discovered by
  Columbus!) by 300 B.C.
• In fact Eratosthenes (ca. 250 B.C.) measured its
  circumference

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St. Augustine, ca. 400 A.D.

• Not only knew that Earth was a sphere
• But worried about the theological issue of the
  Antipodes (the other side of the globe)
• So the physical issue of a spherical Earth was
  well established in Western thought by this time.

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Early replaced with RenaissanceRenaissance
Observations

• First European explorers started to gather
  knowledge on world geography
• Early 1500s E.g., Magellan da Gama

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Renaissance Observations

• Francis Bacon (1561-1626) first noted how coasts
  of Africa and South America fit.

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Today its known Fit best is along their
continental shelves
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The 1800s

• Better maps available
• Some people proposed that all continents could
  fit together
• In 1872, British Challenger began mapping ocean
  floor by soundings
• Similarities in rocks of NW Europe and NE America
  were discovered

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About 1910, the Mid-Atlantic Ridge was discovered
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The Three Paleos
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Paleontology

• The study of fossils

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Evidence from Paleontology

• Similar fossils in
• South America and Africa

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Glossopteris, a seed fern whose seeds are too
large to be carried far by wind
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Mesosaurus, a fresh water reptile that couldnt
swim across the open sea
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Paleoclimatology
The study of ancient climates
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Glaciers in South America, Africa, India, and
Australia...At same time the Northern Hemisphere
had lush swamps...
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and the pieces fit together like a puzzle...

Gondwanaland
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Coal

• Deposits found in Antarctica brrrrr.
• Coal requires a warm, lush climate
• Whats Antarctica like today?

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Paleomagnetism

• Magnetic minerals in molten rock align with
  Earths magnetic field

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Paleomagnetism

• When igneous rock cools, magnetism is frozen
  in, like little compasses...

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Polar Wandering

• Different continents indicate different position
  of North Pole - very strange...
• Only logical explanation is that the CONTINENTS
  have moved since the rocks were formed

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WEGENER and CONTINENTAL DRIFT

• In the 1910s Alfred Wegener put all these pieces
  of evidence together and made the hypothesis of
  CONTINENTAL DRIFT...
• The Origin of Continents and Oceans (1915)
• Hard to give up old ways of thought
• Earth should be reliable, always there, and
  unmoving, terra firma
• E pur si muove Core 2

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CONTINENTAL DRIFT

• When Wegener proposed to fit the continental
  shelves together, rather than the coastlines, we
  got a better fit for all modern continents...

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• Idea All continents have moved to their present
  positions from one supercontinent he called
  
  PANGAEA

- 200 Ma
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Scientific Consensus is that Earth is about

• 4.5 billion years old (4.5 Ga),
• so 200 million years ago isnt so long ago
  about 5 of Earths history
• Perspective, context

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Breakup of Pangaea
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Pangaea at 200 Ma

• Is still just 200/4500 4.5 of Earths history!
• There is evidence of plate movements well before
  this time

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1912 - 1945

• A few geologists looked for more evidence during
  this period...
• Seismologists began studying Earths deeper
  layers and discovered a dense mantle and liquid
  outer core

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WWII and SONAR

• Sonar, developed to find enemy subs, was used in
  the decade after WWII to map the deep sea floor...

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SONAR

• Previously, most geologists thought the sea floor
  was rather flat and featureless
• They were wrong...
• A diverse topography was discovered

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Topography of the Sea Floor
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Topography of the Sea Floor

• Researchers found an undersea mountain range
  40,000 miles long
• And a trenches seven times deeper
  than the Grand Canyon
• Even more striking were the
  geophysical findings...

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Some Geophysics

• Thousands of drilling samples were taken...

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Geophysics

• Paleomagnetism in the deep sea floor rocks
  indicated that many episodes of magnetic
  reversals had taken place...

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These reversals occur in parallel paired bands on
opposite sides of a mid-ocean ridge.

• Radiometric dating showed the rocks get older the
  farther you get from the ridge.

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Sea-Floor Spreading

• In 1962, these data were collected into a theory
  called SEA-FLOOR SPREADING
• New crust forms at mid-ocean ridges...
• Oceanic crust pushes outwards from the ridge and
  (perhaps) takes the continents along

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Earthquakes and Volcanoes

• Seismology is the study of earthquakes

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Earthquakes and Volcanoes

• Data indicate that earthquakes and volcanoes do
  not occur at random locations, rather...

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• Earthquakes and volcanoes occur mostly along or
  near deep ocean trenches and mid-ocean ridges...

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E.g., Pacific Ring of Fire
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Seismology studies

• located a zone of weakness where seismic waves
  travel more slowly
• It was called the asthenosphere.
• The rigid lithosphere sits on top of this

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Finally, a unifying theory...

• In 1968, seismologists at Columbia put all the
  evidence together and came up with the theory of
  PLATE TECTONICS...
• This combined the sub-theories of CONTINENTAL
  DRIFT and SEA-FLOOR SPREADING

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PLATE TECTONICS

• The rigid upper 40 miles or so of Earth
  (lithosphere) is broken up into a dozen or so
  plates, which can slide around on the zone of
  weakness (asthenosphere).

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MECHANISM

• Current idea plates move as a result of mantle
  convection, driven by Earths internal heat

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Why does Earth have internal heat?

• And our Moon doesnt?

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Consequences of Plate TectonicsEarthquakesVolc
anoesMountain Ranges

• Why its a
• Unifying Theory

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FIRST, A FEW DEFINITIONS...
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Types of Plate Boundaries

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• DIVERGENT - pulling apart
• Mid-Atlantic Ridge
• Great Rift Valley of Africa
  

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• Great
• Rift Valley
• of Africa
  

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• CONVERGENT - coming together
• Japan
• Himalaya mountains

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• Himalaya mountains formed when India collided
  with Asia

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• TRANSFORM - slide past each other
• San Andreas Fault
  

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Volcanoes

• Are associated with divergent and convergent
  plate boundaries ...
• Why ?

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• Pacific rim
• Ring of Fire
• Convergent
• and
• Divergent boundaries

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Earthquakes

• Are associated with ALL boundary types ...
• Why ?
• Movement!

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Mountain Building

• Tectonics

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Tectonics

• Comes from the Greek word for building
• - For example, architect master builder or
  technology the study of built things

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Some ages

• And other facts

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Mountain Ranges

• Occur in linear patterns that parallel current or
  former plate boundaries

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Appalachians

• Started forming 400 million years ago (400 Ma)
• Folded sediments and hard rock, but evidently
  worn down by erosion
• Highest elevation Mt. Mitchell - 6,684 ft
• Cumberland Gap

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Rockies

• Started forming 60 Ma
• Highest elevation 14,440 ft (Mt. Elbert)
• Maroon bells, CO

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Himalayas

• Started forming 30 Ma
• Highest elevation 29,035 ft (Mt. Everest)

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Laurentians (in Quebec)

• Canadian Shield
• gt 500 Ma
• Hard rock roots of an ancient mountain range
• Highest elevation 3,825 feet

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MOUNTAIN BUILDING and PLATE TECTONICS
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CONVERGENT BOUNDARY- the Real Deal for mountain
building
Complex mountain system develops---gt Continent
Grows
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http//www.pbs.org/wnet/savageearth/animations/rif
t-subduction.html
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Example The Andes
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GEOCYCLES

• Recycling of matter at or near Earths surface
• Rock cycle
• Lithosphere
• Water cycle
• Hydrosphere
• Weather and Climate
• Atmosphere

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First, the ROCK CYCLE
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Nice Factoids to know How big is our planet?

• Earth is about 8000 miles in diameter
• and 25,000 miles in circumference
• So, it will take you about 20 hours in a jetliner
  at 600 mph to get from Spain to New Zealand

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4 concentric layers

• Inner core (solid)
• Outer core (liquid)
• Mantle (gooey in places)
• Crust (solid) 3-40 miles thick

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What is the Lithosphere and what are the Plates?

• The crust, plus the upper 40 miles of the mantle,
  form the lithosphere, broken into plates which
  slowly slide around on the asthenosphere (zone of
  weakness) via energy from Earths internal heat

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IGNEOUS RXSFire-formed

• Liquid rock is called magma or lava, depending
  on amount of dissolved gas
• INTRUSIVE - cooled under surface
• Examples Granite, Gabbro
• VOLCANIC - cooled at surface
• Examples Basalt, Obsidian, Scoria

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SEDIMENTARY RXSettling

• Clastic - formed from pieces clasts, which come
  from the weathering and erosion of other rock.
• Examples Shale, Sandstone, Conglomerate
• Bio-chemical and Organic
• microskeletons, e.g. in coral reefs Limestone
• Salts in stagnant pools, e.g., Halite
• Organic - decayed remains of plants coal

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METAMORPHIC RXChanged form

• Depends on original rock type and amount of heat
  and pressure
• Shale ----gt Slate or Schist (more heat)
• Granite or dirty sandstone ---gt Gneiss
• Sandstone ----gt Quartzite
• Limestone ----gt Marble

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IGNEOUS RXS andABSOLUTE DATING

• Some igneous rocks can be radiometrically
  dated i.e., have
• an ABSOLUTE AGE assigned (/-)

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On the other handSEDIMENTARY ROCKS

• Are most likely to contain fossils

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But, SEDIMENTARY ROCKS

• Can only be relatively dated

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RELATIVE DATING
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DEEP TIME

• Oceans vs. Puddles

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AIR and WATER
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Water Facts...

• 70 of Earths surface is covered by H2O
• 70 of human bodys weight is H2O
• Water can exist in 3 states on Earths surface
• exists only as solid and vapor on Mars
• only vapor on Venus

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More Water Facts...

• Water freezes at 0 degrees Celsius and boils at
  100 degrees Celsius
• This is higher than similar substances because of
  hydrogen bonding
• Water is most dense at 4 oC. This explains why
  ice floats, which prevents lakes from freezing
  solid in Winter

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Hydrogen Bonding

• ........O H ........
• / \ /
• H H ---- O
• \
• O O H .........
• / \ / \
• H H H H .........

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Water...

• Its heat capacity is higher than similar
  substances
• A watched pot never boils.
• Moderates Earths temperatures
• Compare San Francisco and St. Louis

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AIR

• Main gases in present atmosphere Nitrogen (78),
  Oxygen (21), and Argon (0.9), variable amounts
  of water vapor
• Average sea level atmospheric pressure is 14.7
  pounds per square inch and decreases with altitude

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DISTRIBUTION of EARTHSWATER and AIR
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Origin

• How Impact of Icy Comets and Degassing of
  volatiles ... bottle
• Earths atmosphere was forming 4.4 to 4.0 Ga
• It then (probably) consisted mainly of water
  vapor, carbon dioxide, ammonia, methane (Some
  controversy)

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Brief History

• Icy Comet impacts ---gt add H2O to atmosphere and
  down to about 70km
• Earth cools ---gt Water condenses
• Lots of rain Volcanoes add CO2
• Most of CO2 dissolved in oceans
• Photosynthesizing organisms evolve
• CO2 H2O ------gt C6H12O6 O2

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The Water Cycle

• How Earths water and air interact ...
• Natural recycling process

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The Water Cycle
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ZONES OF CONCENTRATION

• Of natural waters

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ZONES OF CONCENTRATION

• Marine (saltwater)- The oceans contain over 97
  of earths water -- salt water
• Brackish (mixture of salt and fresh)
• Found in estuaries, where fresh and salt water
  meet
• Important to aquatic life
• 3rd most productive ecosystem
• Example Chesapeake Bay

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Fresh Water

• Less than 3 of Earths water is fresh
• Glaciers contain over 75 of Earths fresh
  water, but this source is not usable by life

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Fresh Water

• Lakes and rivers contain less than 1
• Groundwater (including soil moisture) accounts
  for the remaining 24
• If all Earths water fit in a gallon jug, there
  would be one tablespoon of available fresh water

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Structure of the Atmosphere

• Layers classified by temperature changes ...

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The Atmosphere

• All weather occurs in the troposphere
  churning sphere

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Convection causes the churning
Temperature decreases with altitude
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Convection in Humid Air
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Stratosphere

• The ozone layer is contained in the stratosphere
  ...
• No churning because of a temperature
  inversion, i.e.,
• Temperature increases with altitude...

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A l t i t u d e
Stratosphere ---gt Troposphere ---gt
Temperature
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Good Ozone and Bad Ozone

• The same molecule, O3

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The Ozone Layer

• Ozone, O3 , is an air pollutant in the
  troposphere, but in the stratosphere protects us
  from UV radiation
• O3 UV --------gt O2 O
• Chlorine radicals (like from CFCs) interfere
  with this process
• Cl O --------gt ClO

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WEATHER and CLIMATE - Atmosphere Geocycles
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Coriolis Effect

• Caused by an unattached atmosphere over a
  rotating Earth

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Which way does Earth rotate?

• East to West
• Or
• West to East?

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Coriolis Effect
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Coriolis Effect on Winds
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ACTUAL
NON-ROTATING
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PREVAILING WINDS

• The direction the winds blow most of the time
  ...
• Wind direction changes temporarily due to
  weather systems ...
• In the middle latitudes (30o- 60o), the
  prevailing winds are from the west.
• These affect climate as we shall see in a moment
  ...

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PREVAILING WINDS
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OCEAN CURRENTS

• (Surface) currents caused by prevailing winds
  and Coriolis Effect ...
• They play a major role in redistributing Earths
  heat ...
• They are called warm or cold, compared with
  other water at that latitude ...
• Example The Gulf Stream is a warm current.

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OCEAN CURRENTS
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Effects on Climate

• Many factors affect climate
• Prevailing winds and ocean currents are only two
  of these
• Example Why is the weather in Paris more
  pleasant than in Quebec City ?
• Gulf Stream Prevailing westerlies

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Which is farther North?Minneapolis or Venice

• Minneapolis 44.58o N
• Venice 45.27o N
• Whod a thunk it?

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