Exploring the inner and outer shells of earth

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Exploring the inner and outer shells of
earth Chapters 2-3-4
Additional reading MAR discovery, pdf, class web
site
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Learning Objectives Earth structure, Plate
tectonics and Ocean floor  
Difference between oceanic and continental
crust. Understand the processes that are
continuously changing Earths surface as
lithospheric plates move relative to one
another.   Identify the role of oceanic ridges,
transform faults and deep-sea trenches in
defining the edges of lithospheric
plates.   Understand the importance of
asthenospheric thermal convection in plate
tectonics and the resulting compression or
tensional forces at the plate boundaries.   Explai
n the distribution of magnetic anomaly stripes,
seismicity, and volcanism in terms of the concept
of global plate tectonics.   Spreading rates of
ocean basins.
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Earths Structure

• Layered system (like an onion, concentric
  regions)
• differentiation of mineral material

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Earths Structure (contd.)
Classification according to chemical composition

• 4 concentric regions of
• mineral material
• crust
• mantle
• outer core - molten
• inner core - solid

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Earths Structure (contd.)
Classification according to chemical composition

• Crust
• Two types
• continental g granite composed of
• silicates rich in Na, K Al
• ocean g basalt composed of
• silicates rich in Ca, Mg Fe
• represents 0.4 of Earths mass
• extends down to 75 km

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Earths Structure (contd.)
Classification according to chemical composition

• Mantle
• Three parts
• uppermost/middle/innermost
• Composed of Mg-Fe silicates
• represents 68 of Earths mass
• extends down from base of crust to 2,900 km

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Earths Structure (contd.)
Classification according to chemical composition

• Core
• Two parts
• Outer
• Inner
• Composed of Fe Ni
• Represents 28 of Earths mass
• Extends down from base of
• mantle 6400km

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Earths Structure (contd.)
Classification according to physical properties
(factor in temperature and pressure)
4 concentric regions

• lithosphere - rigid outer shell (crust
  uppermost mantle)
• 100 - 150km thick
• does not change shape

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Earths Structure (contd.)

• Asthenosphere - soft, flows over geologic time
  under the weight of the lithosphere (small
  fraction of middle mantle)
• lithosphere floats on top
• zone where magma formed
• 200 350km thick
• easily deformed, can be pushed down by overlying
  lithosphere plastic tar or asphalt

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Earths Structure (contd.)
Classification according to physical properties

• Mesosphere - rigid but not as hard as lithosphere
• higher temp than asthenosphere, but not molten
  because of compression pressure
• 4950km thick

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Earths Structure (contd.)
Classification according to physical properties

1. Core - outer is molten, inner is solid

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Earth consists of a series of concentric layers
or spheres which differ in chemistry and physical
properties.
Chemical Layers
Physical Layers
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Physical state is determined by the combined
effects of pressure and temperature.

• Increasing pressure raises the melting point of a
  material.
• Increasing temperature provides additional energy
  to the atoms and molecules of matter allowing
  them to move farther apart, eventually causing
  the material to melt.
• Both pressure and temperature increase toward the
  center of the Earth, but at variable rates.

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The Oceans of the World
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How do we learn about the inner structure of the
planet?
Seismic waves
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Seismology is the study of elastic waves that
travel through the earth Two main wave types
Compression waves (P-waves) travel by squeezing
and expanding medium they travel through. They
can travel through both solids and liquids (e.g.,
sound waves)
Shear waves (S-waves) travel by shearing
medium they pass through. S-waves can travel
only through solids since particles need to be
bonded to each other to propagate wave
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Earthquake are an incredible source of seismic
waves

• Seismic waves travel
• along the quickest
• route, generally
• through the planetary
• interior to the seismic
• stations, changing
• speed every time
• material properties
• change.

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Reconstructing the internal structure of the
planet
solid

• Crust upper mantle large increases in seismic
  velocities and density

solid, more dense

• Mantle Gradual velocity and density increase

Liquid Iron

• Outer core dramatic density increase and no
  S-waves

• Inner core Jump in density and P-wave velocity,
  S-waves return

solid Iron
Other planets?
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Earthquakes produce waves in the ocean
Sea level RISE FALL
Courtesy K. Satake, unpublished
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World Seismicity

• (1898-2003)

Mw 6.0
Mw 7.7
Many large earthquakes occur along subduction
zones
Most Great earthquakes are subduction
mega-thrust events
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The Physiography of the North Atlantic Ocean Floor
continental margins
deep ocean basins
midoceanic ridges
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Mid Atlantic Ridge new findings

• http//www.noc.soton.ac.uk/gg/classroom_at_sea/JC007/
  about.html
• http//www.sciencedaily.com/releases/2007/03/07030
  1103112.htm
• http//www.noc.soton.ac.uk/gg/classroom_at_sea/JC007/
  background.html

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MAR discovery - http//alpha.es.umb.edu/faculty/af
/intro_ocean.htmUnit1
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Type of continental margins
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• Continental margins are the submerged edges of
  the continents and consist of massive wedges of
  sediment eroded from the land and deposited along
  the continental edge. The Continental Margin can
  be divided into three parts the Continental
  shelf, the Continental slope, and the Continental
  rise.

Passive Continental Margin
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• Midoceanic Ridge Province consists of a
  continuous submarine mountain range that covers
  about one third of the ocean floor and extends
  for about 60,000 km around the Earth.

Midocean Ridge
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• Deep Ocean Province is between the continental
  margins and the midoceanic ridge and includes a
  variety of features from mountainous to flat
  plains Abyssal plains, Abyssal hills, Seamounts,
  and Deep sea trenches.

Deep Ocean Basin
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Hydrothermal Vents
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03_13a
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This three-dimensional rendition of a bathymetric
map shows Patton Seamount, a Gulf of Alaska
seamount we visited in 1999, with two smaller
seamounts in the foreground. Deep areas are blue,
and shallow areas are red.
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WHY DO LAND AND OCEAN EXIST?
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Continents and ocean basins differ in
composition, elevation and physiographic features.
Geologic Differences between Continents and Ocean
Basins
2-3

• Elevation of Earths surface displays a bimodal
  distribution with about 29 above sea level and
  much of the remainder at a depth of 4 to 5
  kilometers below sea level.
• Continental crust is mainly composed of granite,
  a light colored, lower density, igneous rock rich
  in aluminum, silicon and oxygen.
• Oceanic crust is composed of basalt, a dark
  colored, higher density, volcanic rock rich in
  silicon, oxygen and magnesium.

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Geologic Differences between Continents and Ocean
Basins
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WHY DO LAND AND OCEAN EXIST?
OCEANIC CRUST THIN AND DENSER CONTINENTAL CRUST
THICK AND LEIGTHER
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• Continents are thick (30 to 40 km), have low
  density and rise high above the supporting mantle
  rocks.
• Sea floor is thin (4 to 10 km), has greater
  density and does not rise as high above the
  mantle.

Oceanic Crust Versus Continental Crust
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Isostacy Principle that dictates how different
parts of the lithosphere stand in relation to
each other in the vertical direction

• Continental crust less dense (granitic) therefore
  rises higher relative to ocean crust (basaltic)
• Continents move up and down depending on weight
  on top (i.e. from glaciers - isostatic rebound)
• Continents pop up after glaciers melt
• Canada and Scandinavia rising at a rate of
  1m/100yrs because the glaciers are receding

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Isostasy refers to the balance of an object
floating upon a fluid medium. Height of the
mass above and below the surface of the medium is
controlled by the thickness of the mass and its
density (similar to ice floating in water).
http//atlas.geo.cornell.edu/education/student/iso
stasy.html http//woodshole.er.usgs.gov/operation
s/modeling/movies/fli/stellrise.flc
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altimetry Satellites in orbit around the planet
use radar altimetry to measure the height of the
sea level (accuracy of 2 cm).
http//www.ecco-group.org/animations_iter21/TP_ps2
1.mpeg
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Model of the shape of the Earth
geoid The equipotential surface of the Earth's
gravity field which best fits, in a least squares
sense, global mean sea level (MSL)
http//www.esri.com/news/arcuser/0703/geoid1of3.ht
ml
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Why ocean bathymetry?
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Ocean Circulation and Climate Deep ocean mixing
and pathways
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Social impacts Tsunami
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Social impacts Gas and oil extraction