Earth s Interior
EARTHQUAKES
Seismic Waves and Earth s Structure Abrupt changes in seismic-wave velocities that occur at particular depths helped seismologists conclude that Earth must be composed of distinct shells.
Possible Paths of Seismic Waves
1999 Prentice Hall
Three compositional layers 1. Crust is the comparatively thin outer skin that ranges from 3 kilometers (2 miles) at the oceanic ridges to 70 kilometers (40 miles) in some mountain belts. With increasing depth, Earth s interior is characterized by gradual increases in temperature, pressure, and density.
Three compositional layers 2. Mantle is a solid rocky (silica-rich) shell that extends to a depth of about 2900 kilometers (1800 miles). With increasing depth, Earth s interior is characterized by gradual increases in temperature, pressure, and density.
Three compositional layers 3. Core is an iron-rich sphere having a radius of 3486 kilometers (2161 miles). With increasing depth, Earth s interior is characterized by gradual increases in temperature, pressure, and density.
2007 W.H. Freeman 2004 Pearson Prentice Hall Crust
Seismic Waves and Earth s Structure Depending on the temperature and depth, a particular Earth material may behave like a brittle solid, deform in a plastic like manner, or melt and become liquid.
Layers are defined by physical properties. Lithosphere (sphere of rock) Earth s outermost layer Consists of the crust and uppermost mantle Relatively cool, rigid shell Averages about 100 kilometers in thickness.
Layers are defined by physical properties. Asthenosphere (weak sphere) Beneath the lithosphere, in the upper mantle to a depth of about 600 kilometers. Lithosphere moves independently of the asthenosphere.
Layers are defined by physical properties. Mesosphere or lower mantle Rigid layer between the depths of 660 kilometers and 2900 kilometers.
Layers are defined by physical properties. Outer core Composed mostly of an iron-nickel alloy. Liquid layer. 2270 kilometers (1410 miles) thick. Generates Earth s magnetic field.
Layers are defined by physical properties. Inner core Sphere with a radius of 3486 kilometers (2161 miles). Stronger than the outer core. Behaves like a solid.
Rigid Lithosphere Plastic Asthenosphere Rigid Mesosphere Liquid Outer Core Solid Inner Core 2004 Pearson Prentice Hall 2004 Pearson Prentice Hall
Discovering Earth s Major Boundaries The Moho (Mohorovicic discontinuity) Discovered in 1909 by Andrija Mohoroviĉiĉ. Separates crust from mantle. Identified by a change in P-wave velocity.
Discovering Earth s Major Boundaries The core mantle boundary Discovered in 1914 by Beno Gutenberg. Based on the observation of P-wave shadow zone. Also causes an S-wave shadow zone.
P-Wave Shadow Zone
S-Wave Shadow Zone
Two Kinds of Crust Oceanic crust Thin and dense. Continental crust Thick and buoyant.
2004 Pearson Prentice Hall
1999 Prentice Hall
MAJOR TECTONIC PLATES 2011 Pearson Education, Inc.
MAJOR TECTONIC PLATES
PLATE BOUNDARY INTERACTIONS W.W. NORTON & CO.
Continental rifts: the initiation of a divergent margin
PLATE BOUNDARY INTERACTIONS W.W. NORTON & CO.
Three types of convergent margins Ocean-Continent Ocean-Ocean Continent-Continent
SUBDUCTION Once oceanic lithosphere has cooled for 10 million years it becomes dense enough to subduct. If the oceanic plate bends down it can begin to sink into the asthenosphere like an anchor into water.
Hamblin & Christiansen, 2004
Seismic Tomographic Slice Through the Earth 2011 Pearson Education, Inc.
Three types of convergent margins Ocean-Continent Ocean-Ocean Continent-Continent
Oceanic Continental Convergence 2011 Pearson Education, Inc.
Three types of convergent margins Ocean-Continent Ocean-Ocean Continent-Continent
Convergent Plate Boundaries 2011 Pearson Education, Inc.
Three types of convergent margins Ocean-Continent Ocean-Ocean Continent-Continent
Continental Continental Convergence 2011 Pearson Education, Inc.
PLATE BOUNDARY INTERACTIONS W.W. NORTON & CO.
Transform Boundaries Places where the plates slide past each other. Common offset mid-ocean ridge crests.
Plate margin interactions explain most geology, but there is another piece of the story missing: Observation: linear volcanic chains within plates.
Active Volcano
PLATE BOUNDARY INTERACTIONS? W.W. NORTON & CO.
Hot Spots A Hot Spot is an area of mantle upwelling that is fixed with relationship to the overlying plate. The hot spot stays in one place, and burns its way through the overriding, moving plate, leaving a trail of volcanoes in its wake. The volcanoes get older, become inactive, and sink, as you move away from the active hot spot.
Not all hotspots are in oceanic crust Yellowstone!
Hamblin & Christiansen, 2004
Forces Driving Plate Motions 2011 Pearson Education, Inc.
RIDGE-PUSH AND SLAB-PULL FORCES
Model of Convective Flow in the Mantle 2011 Pearson Education, Inc.