A View of Earth

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A View of Earth
Luc Ikelle 2012
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A View of Earth (Apollo 17)
Dry lands (deserts)
oceans
Wetter climate
Antarctica Glacial ice
Ocean and atmosphere
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Earths spheres (1)

• The most dynamic portion of Earth
• Atmosphere
• Thin gaseous envelope surrounding Earth
• Hydrosphere
• Water dominated by the oceans
• Biosphere
• All living things on the planet
• Lithosphere
• Rocky outer shell

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Earths spheres the atmosphere (2)

• Composition is unique in the solar system
• Provides Air we breathe and protects from the
  Suns intense heat.
• Thin (90 in 16 km) and tenuous
• 78 nitrogen
• 21 oxygen (not present in early atmosphere)
• Minor amounts of carbon dioxide, argon and water
  vapor

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Earths spheres the hydrosphere (3)
(blue planet)

• Total mass of water on or near Earths surface
• Covers 71 of Earths surface
• 98 in oceans
• 2 in glaciers, groundwater, lakes and streams
  (fresh water)

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Earths spheres the biosphere (4)

• All life on Earth
• Animals plants on land, in the sea and air
  (tree roots, flying insects and birds, )
• There life in ocean floor the pressure
• is extreme and no light penetrate.
• Microorganisms - the most common form of life
• Evolved within narrow zone near the Earths
  surface

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A view of Earth

• Earths spheres
• Earths interior description
• Earths interior evidence
• Major features of Earths surface

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Earths internal structure

• Solid Earth has a layered structure
• Layers defined by composition and physical
  properties
• Compositional layers
• crust - mantle - core
• Physical layers
• lithosphere - asthenosphere - mesosphere - outer
  core - inner core

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Compositional Layers

• Crust
• Outermost compositional layer
• Definite change in composition at the base of the
  crust
• 2 types
• Continental crust (up 75 km thick in Himalaya),
• Oceanic crust ( 8 km thick)

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Compositional Layers

• Mantle
• Largest layer in the earth
• 2900 km thick
• 82 by volume
• 68 by mass
• Composed of silicate rocks with abundant iron and
  magnesium
• Density ranges from 3.2 to 5 g/cc

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Compositional Layers

• Core
• Central mass about 7000 km in diameter
• Average density of 10.8 g/cc
• 16 by volume, 32 of mass
• Indirect evidence of composition
• Metallic iron

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Lithosphere/asthenosphere
Lithosphere crust uppermost part of the
mantle Astenosphere part of the mantle beneath
the lithosphere
Continental crust
Oceanic crust
Lithosphere mantle
Asthenosphere
Lithosphere
The uppermost part of the mantle is strong and
solidly attached to crust).
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Physical layerslithosphere

• Crust upper portion of the mantle
• Solid rigid
• Thickness ranges from 10 km beneath oceans to 300
  km in continental areas

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Physical layerscontinental crust

• Thick - up to 75 km
• Lower density - 2.7 g/cm3
• Strongly deformed
• Much older - may be billions of years old

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Physical layersoceanic crust

• Thinner - about 8 km
• More dense - 3.0 g/cm3
• Comparatively undeformed
• Much younger lt 200 million years old

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A view of Earth

• Earths spheres
• Earths interior description
• Earths interior evidence
• Major features of Earths surface

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Waves

• Elastic waves are generated whenever there is
• a sudden deformation
• a sudden movement of a portion of the medium

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Waves

• Examples of man-made seismic sources
• Explosion
• Weight drop
• Drilling
• Vibroseis (tractions), ...

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Two types of deformations

• Volumetric change
• (P-waves, compressional waves)
• Change of shape
• (S-wave, shear waves)

Source Duan (2010)
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P-waves (compressional waves)

• P-waves (i) similar to sound waves, (ii) series
  of contractions and relaxations, (iii) fastest,
  5 km/sec (depends on rock type), (iv) travel
  through solid, liquid and gas

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S-waves (shear waves)

• S-waves motion is (i) right angles to direction
  of wave, (ii) about half the speed of P waves,
  and (iii) travel only through solids

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P-wave
S-wave
Source Duan (2010)
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Horizontal source
Source petroleum-seismology.com
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Sea surface (marine/offshore)(Air/water/solid)
Source petroleum-seismology.com
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Free surface (land/onshore)(Air/solid/solid)
Source petroleum-seismology.com
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Exploring Earths interior with seismic waves

• Seismic waves travel at different speeds in
  different rocks

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Seismic waves ground shaking

• Surface waves propagate near the Earth surface,
  slower than body waves
• L-waves Love, move back/forth (snake)
• R-waves Rayleigh, move like ripples on a pond

Source Duan (2010)
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Source Duan (2010)
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Recording seismic waves seismograms

• Seismograms records of ground shaking
• Waves arrive in sequence.
• P waves first
• S waves second
• Surface waves last (cause most of the property
  damage in an earthquake).

Source Duan (2010)
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Interior with seismic waves

• Discovery of Core-Mantle boundary P-waves do not
  arrive in the P-wave shadow zone (103 143)

Source Duan (2010)
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Interior with Seismic Waves (cont.)

• Discovering two parts of the core liquid outer
  core solid inner core
• S-waves do not arrive in the S-wave shadow zone
• P-wave reflection within the core

Source Duan (2010)
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Source Duan (2010)
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refraction
Source Duan (2010)
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A View of Earth

• Earths spheres
• Earths interior description
• Earths interior evidence
• Major features of Earths surface

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World map
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World map
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World map
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North and Central Americas
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Central America
Caribbean sea
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South America
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Europe
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Africa
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Asia
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Oceania
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Some Additional Statistics
Average land elevation 840 m Average ocean
depth 3,800 m
Average ocean temperature 3.9oC
About 50 of Earths population lives lt240 km
from the ocean

• In Japan, 96 of the population lives lt100 km
  from the ocean

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• Kola Superdeep Borehole (KSDB)
• A scientific drilling project in the USSR to
  drill into the Earth's crust
• goal 15 km
• began digging in 1970
• in 1992, reached a final depth of 12 km

• 245oC!

lt1/500 of Earths radius
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Problems

• How do we know that the outer core is liquid?
• Is the core a constituent of the asthenosphere?
• List and briefly describe the four spheres that
  constitute our environment.
• Can P-wave velocity be greater than S-wave
  velocity?
• Can S-wave propagate in the sea water?
• Is Guatemala in North, Central, or South America?
• Where is the Gulf of Aden?
• Which one of these components (crust, mantle,
  core) of Earth is the heaviest?
• Which one of these components (crust, mantle,
  core) occupies the largest volume of Earth.
• Which one of these components (oceans and
  continents) occupies the largest portion of the
  surface Earth.