Download 1 Midterm Exam I September 26, 2:10 HW714

Midterm Exam I
September 26, 2:10 HW714
Questions from the Concept Check (CC) boxes in
textbook:
¾ Chapters 1, 2, 3 and 4
¾ 60 multiple choice questions
¾ this exam constitutes 22% (only) of your
total (overall) grade
Chapter 1: 2,3,4, 8,11,14,15 - Read about historical
developments in oceanography in USA.
Chapter 2: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 and 14.
Please Note:
1. I will not be in class for this exam. The exam will be administered by Ms
Dana Reimer and her assistant, both are experienced instructors. You should
not need them to answer questions beyond clarifications of text at the most.
Grades will be available at our next class, October 3rd.
2. Remember to bring pencils!!! (No. 2) and to follow the instructions about
writing your names on both exam and answer sheets, as well as to ‘bubble’ your
names (no IDs!) on the appropriate place of the answer sheet (on the back).
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Chapter 3: 1, 2, 4, 5, 7, 8, 9, 10, 11, 12, 13, 16, 17, 18, 19, 20,
21, 23, 24 and 25. Read the textbook discussion of how
the theory of plate tectonics developed over time.:
Chapter 4: 2, 3, 4, 6, 7, 8, 9, 10, 11, 13, 15, 17 and 20.
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Relative amount of water
in the different reservoirs
on Earth’s surface
Mid-Atlantic
Ridge
The average depth of the ocean is
4 ½ times as great as average land
elevation (about 840 m or ½ mile).
Note the extent of the Pacific
Ocean, Earth’
Earth’s most prominent
single feature.
Ocean’s
deepest
spot
Earth’s
highest
mountain
Pacific Ocean Basin
Earth’s largest
feature
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4
1
North
Pole
Understanding the Ocean Began with Voyaging for
Trade and Exploration
¾ Voyaging on water was important to many early civilizations. The
60°
N
Latitude
30°
N
Egyptians, Cretans, and Phoenicians were all skilled sailors.
¾ Cartographers,
Cartographers, or chart makers, recorded information about locations
Latitu
de
and landmarks and currents. Charts are detailed graphic
representations of water and waterwater-related information.
0
°
Equat
or
¾ The Library at Alexandria,
Alexandria, in Egypt, was founded in the third century
B.C. This library stored information on every area of human endeavor.
endeavor.
¾ Eratosthenes of Cyrene was the second librarian at Alexandria. He
30°
S
South
Pole
was the first to calculate the circumference of Earth. He also invented
invented
a system of longitude and latitude.
Determining Longitudes
¾ The principles of celestial navigation were invented at the Library at
Alexandria.
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Formation of the Earth
Longitude and Time
• Big Bang 13*109 years ago
The clock is set to
noon when the Sun is
at its zenith above
the prime meridian
•
•
•
¾ Formation of elementary particles
¾ Gravitational formation of dense regions
stars
12*109 years ago
First
Earth
Water
4.6*109 years ago
3.9*109 years ago
109 = 1 billion year
Every 15° of
longitude
correspond to 1
hour
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• Sources of Water:
¾Mantle rocks
¾Outer space
• Earth’s shape – Oblate Spheroid
• average radius ~ 6400 km
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2
Earth, Ocean and Atmosphere accumulated in layers sorted by
density
The planet grew by the aggregation of particles.
Meteors and asteroids bombarded the surface,
heating the new planet and adding to its growing
mass. At the time, Earth was composed of a
homogeneous mixture of materials.
How did water and water vapor form on early
Earth?
¾ The Sun stripped away Earth’
Earth’s first atmosphere
¾ Gases, including water vapor, released by the
process of outgassing,
outgassing, replaced the first
atmosphere.
¾ Water vapor in the atmosphere condensed into
clouds.
¾ After millions of years, the clouds cooled enough for
water droplets to form.
¾ Hot rain fell and boiled back into the clouds.
¾ Eventually, the surface cooled enough for water to
collect in basins.
Earth lost volume because of gravitational
compression. High temperatures in the interior
turned the inner Earth into a semisolid mass;
dense iron (red drops) fell toward the center to
form the core, while less dense silicates move
outward. Friction generated by this movement
heated Earth even more.
The result of density stratification:
an inner
and
outer core,
a mantle,
and the crust.
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The evolution of our atmosphere
Age and Time
1 billion = 1,000,000,000 or 109
Earth is 4.6 * 109 years old
Oceans are 4.2 * 109 years old
Oldest rocks date from 3.8 * 109 years ago
First evidence of life dates from 3.6 * 109
years ago
1 million = 1,000,000 or 106
Ocean and atmosphere reach the state we
know today 800 * 106 years ago
100
Concentration of
Atmospheric Gases (%)
Methane, ammonia
75
Atmosphere
unknown
initial rise of O2 2.7 b. y. ago – but conclusive
evidence is from 2.3 b. y. ago
Nitrogen
50
Water
25
Carbon dioxide
0
4.5
Oxygen
3
4
Time (billions of years ago)
2
Early atmosphere quite different from today’s
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Fig. 2-11,11p. 49
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Evidence for layered Earth
- Seismic wave:
Chapter 3
P waves = Primary Waves
• Geologic Structure of Earth
• Continental Drift – Seafloor Spreading
• Mantle Convection - Plate Tectonics
S waves = Secondary Waves
Density measures
the mass
per unit volume of
a substance.
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Lithosphere & Asthenosphere:: More detailed
description of Earth’s layered structure according
to mechanical behavior of rocks, which ranges from
very rigid to deformable
1. lithosphere: rigid surface
shell that includes upper
mantle and crust (here is
where ‘plate tectonics’
work), cool layer
2. asthenosphere: layer
below lithosphere, part of
the mantle, weak and
deformable (ductile,
deforms as plates move),
partial melting of material
happens here, hotter layer
(100 – 200 km)
(200 – 400 km)
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The layers:
1. Core: 3500 km thick, average density
13 g/cm3, 30% of Earth’s mass and 16%
of its volume
¾Inner core: primarily iron & nickel
¾Outer core: liquid (partially melted)
3. Mantle: Magnesium and iron, less
dense, solid but can flow;70% Earth’s
mass & 80% of its volume, 2866 km
thick, @ Temp of 100-3200°C
4. Crust – rigid, thin outer layer; 0.4% of
Earth’s mass and 1% of its volume
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Earth’
Earth’s outer layer is the Crust: cool, rigid (brittle), thin
surface layer – rocks on crust side are chemically different
than rocks on mantle side – separation between crust and
mantle is called Mohorovičić discontinuity (the Moho)
Moho) – two
types:
1. Continental Crust:
* 40km thick on average
* Relatively light
2. Oceanic Crust
* 7km thick
* Relatively dense
Buoyancy: depends on the mass and density of the object
and of the liquid in which object floats
Isostasy: state of gravitational equilibrium between the
lithosphere and asthenosphere such that the tectonic
plates “float” at an elevation that depends on their
thickness and density.
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4
Model of Mantle Convection
Continental Drift – Seafloor Spreading
Evidence from
spreading centers – where new sea floor and oceanic lithosphere form
subduction zones – where old oceanic lithosphere descends
1. Earthquake epicenters
2. Heat flow *Review Figure*
3. Radiometric dating of rocks of ocean and continental
crust *Review Figure*
4. Magnetism
¾
¾
¾
Earth’s outer layer is divided into lithospheric plate
Earth’s plates float on the asthenosphere
Plate movement is powered by convection currents in the
asthenosphere seafloor spreading, and the downward pull of a
descending plate’s leading edge.
Hess and Dietz in 1960 proposed a model to explain
features of ocean floor and of continental motion
powered by heat Æ mantle convection
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Earthquake Epicenters
Improved Mapping, WWII
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As plates float on the deformable
aesthenosphere,
aesthenosphere, they interact among
each other. The result of these
interactions is the existence of 3
types of boundaries:
Shallow epicenters – crustal movement
(less than 100 km)
Mid-deep epicenters – subduction
(greater than 100 km)
Plates Æ Rigid Slabs of Rock
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(a) Divergent: plates move away from each
other, examples:
* Divergent oceanic crust:
the Mid-Atlantic Ridge
* Divergent continental crust:
the Rift Valley of East Africa
(b) Convergent: plates move toward each
other.
Three possible combinations:
continent-ocean, ocean-ocean,
continent-continent
(c) Transform:
neither (a) nor (b), plates slide
past one another – transform faults.
* Example: San Andreas fault
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5
Symmetrical pattern around Mid-Ocean Ridges
Oceans are created along divergent boundaries
2 kinds of plate divergences
3 kinds of plate convergences
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Magnetic field direction changes
through geologic time and these
polar reversals recorded in rocks
Motion of the plates:
plates:
Mechanisms – not fully understood
Rates: average 5 cm/year
MidMid-Atlantic Ridge = 2.5 – 3.0 cm/yr
EastEast-Pacific Rise = 8.0 – 13.0 cm/yr
Many discoveries contribute to the theory of
plate tectonics but the most compelling evidence
comes from The Earth’s Magnetic Field
At the Curie
Point, 560 °C,
rock solidifies and
captures magnetic
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signature
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Plate Movement above Mantle Plumes and Hot
Spots Provides Evidence of Plate Tectonics
Chapter 4
Continental Margins and Ocean Basins
ƒ
ƒ
ƒ
ƒ
ƒ
Bathymetry of Sea Floor
Continental Margins and Ocean Basins
Submarine Canyons
Hydrothermal Vents
Trenches
Volcanic island chains form as an oceanic plate moves over a stationary
mantle plume and hot spot. Example: Hawaiian Islands.
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LIDAR: Light Imaging Detection And Ranging
Bathymetry: a map of the ocean floor
Vw ~= 1500 m/s (Pres, Temp, Salinity)
Use SOUND (how?) to map ocean floor
Va ~= 344 m/s (Pres, Temp, other)
ƒ Echo sounding
ƒ Multibeam Systems
ƒ Satellite Altimetry
Satellite altimetry and use
light (how?) to map ocean floor
Echo Sounders Bounce Sound off the Seabed
Vw ~= 1500 m/s
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Using satellite
measurements to map the
ocean floor
Write
three
sentences
to convey
the
information
summarized
in this
chart
Analysis of Gravitational
Anomalies (how?) is used to
obtain the bathymetry of ocean
floorfloor-ridges, shelves
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An active
margin
Describe this picture and define all items
Continental
margin
Peru–Chile
Plate
Trench
boundary
Nazca Plate
Submarine canyon profile (cut
through continental shelf)
Sediment
Continental shelf
Continental slope Oceanic
ridge
Continental rise
Sediment
Continental
crust (granitic)
Continental
crust (granitic)
Oceanic
crust (basaltic)
Asthenosphere
Plate
movement
A
passive
margin
Andes
Plate boundary
Mountains
Broad
South America continental shelf
Atlantic
Ocean
South American
Deep basin
Plate
Afr
Pacific Ocean
Continental
margin
Deep-ocean basin
Narrow
continental
shelf
ican Plate
Plate
movement
Subduction zone
(deep and shallow
earthquakes)
Plate
movement
Mid-Atlantic Ridge
(spreading centers,
shallow earthquakes)
• Atlantic = Passive Margin; little/no geologic
activity
Oceanic
crust (basaltic)
• Pacific = Active Margin; geologic activity
Describe this picture and define all items
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The ocean floor can be classified as
Continental Margins
(a)
Continental Margins – the submerged outer edge of a
continent
(b) Ocean Basin – the deep seafloor beyond the continental
margin
There are two types of continental Margins
(a) passive or trailing margins: margin of continent that
moves away from spreading center – Atlantic-style margins
(also Artic Ocean, Antarctica and Indian Ocean). Very little
volcanic or earthquake activity is associated with passive
margins.
(b) active or leading margins: plate boundary located along a
continental margin – ocean trenches where there is
subduction of oceanic lithosphere – narrow, steep, with
volcanic mountains (West Coast of the Americas). Active
margins are the site of volcanic and earthquake activity. 31
• Region where continental crust meets oceanic crust
• Continental Shelf
• Shelf Break
• Continental Slope
• Continental Rise
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Anatomy of a passive margin
Continental Margins
Continental shelvesÆ
shelvesÆ Gently sloping (~0.5 degrees)
Depositional environments
Average width 65 km (40 miles)
Average depth 130 m (430 feet)
Narrow(Wide) along Active(Pasive)
margins
(~ 140 m)
Shelf Break Æ
Continental Slope Æ Extends from break to ocean basin
Steep (3 – 6 degrees, As high as 25 deg.
Little/no deposition
deep
sediments accumulate here, thickness varies
Edge of the continental shelf
Change in slope
Continental Rise Æ Base of the continental slope
slope 0.5 – 1 degree
Depositional environment
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Submarine Canyons Form at the Junction between
Continental Shelf and Continental Slope
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Turbidity Currents - Fast moving avalanches of mud
and sand scour slopes; form turbidite deposits; 90
km/hr (56 mi/hr)
These are features of some continental margins. They cut
into the continental shelf and slope, often terminating on
the deep-sea floor in a fan-shaped wedge of sediment.
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Features of the Sea floor
Basins Æ
sections of the abyssal plain separated
by continental margins, ridges, and rises.
Oceanic Ridges
Hydrothermal Vents
Abyssal Plains and Abyssal Hills
Seamounts and Guyots
Trenches and Island Arcs
Seafloor:
Seafloor: 4000 – 6000 m water depth, 30% of the
Earth’
Earth’s surface
Abyssal Plain: vast, flat plain extending from the base of
the continental slope.
Ocean Basins: sections of the abyssal plain separated by
continental margins, ridges, and rises.
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Sea floor features
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FlatFlat-topped seamounts eroded by
wave action are called guyots.
guyots.
Seamounts are volcanic projections from the ocean floor that do not
rise above sea level. FlatFlat-topped seamounts eroded by wave action are
called guyots
Abyssal hills are small, extinct volcanoes or
rock intrusions near the oceanic ridges.
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Abyssal hills are flat areas of sedimentsediment-covered ocean floor found
between the continental margins and oceanic ridges. Abyssal hills are
small, extinct volcanoes or rock intrusions near the oceanic ridges.
ridges. 40
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MidMid-Ocean Ridges and Rises
Hydrothermal vents are sites where superheated water containing
dissolved minerals and gases escapes through fissures, or vents. Cool
water (blue arrows) is heated as it descends toward the hot magma
magma
chamber, leaching sulfur, iron, copper, zinc, and other materials
materials from
the surrounding rocks. The heated water (red arrows) returning to
to
the surface carries these elements upward, discharging them at
hydrothermal springs on the seafloor.
An oceanic ridge is a mountainous chain of young,
basaltic rock at an active spreading center of an ocean.
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Major ocean trenches
Trenches are arcarc-shaped depressions in the ocean floor caused by the
subduction of a converging ocean plate.
Most trenches are around the edges of the active Pacific. Trenches
Trenches are the
deepest places in Earth’
Earth’s crust, 3 to 6 kilometers (1.9 to 3.7 miles) deeper than
the adjacent basin floor. The ocean’
ocean’s greatest depth is the Mariana Trench
where the depth reaches 11,022 meters (36,163 miles) below sea level.
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level.
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Chapter 4 - Summary
• Bathymetric devices used to study seabed features
include multibeam echo sounder systems and satellites
that use sensitive radar for altimetry.
• Seafloor features result from a combination of tectonic
activity and the processes of erosion and deposition.
• Near shore, the features of the ocean floor are similar
to those of the adjacent continents because they share
the same granitic basement. The transition to basalt
marks the edge of the continent and divides ocean
floors into two major provinces, The submerged outer
edge of a continent is called the continental margin.
The deepdeep-sea floor beyond the continental margin is
called the ocean basin
• Features of the continental margins include continental
shelves, continental slopes, submarine canyons, and
continental rises.
• Features of the deepdeep-ocean basins include oceanic
ridges, hydrothermal vents, abyssal plains and hills,
seamounts, guyots,
guyots, trenches, and island arcs.
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