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A View of Earth
Luc Ikelle
2012
A View of Earth (Apollo 17)
Dry lands (deserts)
oceans
Wetter climate
Antarctica:
Glacial ice
Ocean and atmosphere
Earth’s 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
Earth’s spheres: the atmosphere (2)
Composition is unique in the solar system
– Provides Air we breathe and protects from
the Sun’s 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
Earth’s spheres: the hydrosphere (3)
(blue planet)
Total mass of water on or near Earth’s
surface
– Covers 71% of Earth’s surface
– ~98% in oceans
– 2% in glaciers, groundwater, lakes and
streams (fresh water)
Earth’s 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
Earth’s surface
A view of Earth
• Earth’s spheres
• Earth’s interior: description
• Earth’s interior: evidence
• Major features of Earth’s surface
Earth’s 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
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)
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
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
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).
Physical layers:
lithosphere
– Crust + upper portion of the mantle
– Solid & rigid
– Thickness ranges from 10 km beneath
oceans to 300 km in continental areas
Physical layers:
continental crust
• Thick - up to 75 km
• Lower density - 2.7 g/cm3
• Strongly deformed
• Much older - may be billions of years old
Physical layers:
oceanic crust
• Thinner - about 8 km
• More dense - 3.0 g/cm3
• Comparatively undeformed
• Much younger < 200 million years old
A view of Earth
• Earth’s spheres
• Earth’s interior: description
• Earth’s interior: evidence
• Major features of Earth’s surface
Waves
• Elastic waves are generated whenever there is
– a sudden deformation
– a sudden movement of a portion of the medium
Waves
• Examples of man-made seismic sources
– Explosion
– Weight drop
– Drilling
– Vibroseis (tractions), ...
Two types of deformations
• Volumetric change
(P-waves, compressional
waves)
• Change of shape
(S-wave, shear waves)
Source: Duan (2010)
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
Source: Ikelle and Amundsen (2005); IPS
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
Source: Ikelle and Amundsen (2005); IPS
P-wave
S-wave
Source: Duan (2010)
Horizontal source
1.5 km
2.5 km
Source: petroleum-seismology.com
Sea surface (marine/offshore)
(Air/water/solid)
2.5 km
Source: petroleum-seismology.com
Free surface (land/onshore)
(Air/solid/solid)
1.5 km
2.5 km
Source: petroleum-seismology.com
Exploring Earth’s interior with
seismic waves
• Seismic waves travel at different speeds in
different rocks
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)
Source: Duan (2010)
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)
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)
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)
Source: Duan (2010)
refraction
Source: Duan (2010)
A View of Earth
• Earth’s spheres
• Earth’s interior: description
• Earth’s interior: evidence
• Major features of Earth’s surface
World map
World map
World map
North and Central Americas
Central America
Caribbean sea
South America
Europe
Africa
Asia
Oceania
Arctic Ocean
Pacific Ocean
Atlantic
Ocean
Indian Ocean
All oceans and seas together = the “world ocean”
Northern Hemisphere
• 61% ocean
Equator
Southern Hemisphere
• 81% ocean
http://www.uwsp.edu/geO/faculty/ritter/geog101/textbook/images/maps/oceans_CIA_base.jpg
BUT, on a planetary scale, the ocean is small
• 0.13% of Earth’s volume
• more water within Earth’s interior than in its ocean and
atmosphere
Some Additional Statistics
Average land elevation = 840 m
Average ocean depth = 3,800 m
Average ocean temperature = 3.9oC
About 50% of Earth’s population lives
<240 km from the ocean
• In Japan, 96% of the population
lives <100 km from the ocean
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!
<1/500 of
Earth’s radius
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.