A View of Earth Luc Ikelle 2012
A View of Earth (Apollo 17) Dry lands (deserts) oceans Wetter climate Ocean and atmosphere Antarctica: Glacial ice
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) Total mass of water on or near Earth s surface Covers 71% of Earth s surface ~98% in oceans (blue planet) 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
Crust Compositional Layers 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)
Mantle Compositional Layers 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
Core Compositional Layers 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/cm 3 Strongly deformed Much older - may be billions of years old
Physical layers: oceanic crust Thinner - about 8 km More dense - 3.0 g/cm 3 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)
1.5 km Horizontal source 2.5 km Source: petroleum-seismology.com
Sea surface (marine/offshore) (Air/water/solid) 2.5 km Source: petroleum-seismology.com
1.5 km Free surface (land/onshore) (Air/solid/solid) 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 http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/images/maps/oceans_cia_base.jpg 81% ocean 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 = 3.9 o C 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 245 o C! <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.