Download Earth`s interio

The Earth’s Interior
• Radius: 6,370 Km (4,000 miles)
• Crust, Mantle, Core
– Temperature in core is ~4000 C.
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Most of what we know is from geophysics
Evidence from Seismic Waves
• Velocity of waves in various rock types and rock density
– Typical P wave velocities:
• Basalt 7 Km/sec
• Granite 6 Km/sec
• Limestone 5 Km/sec
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Seismic Reflection
Seismic Refraction
Earth’s Internal Structure
• The Earth’s Crust
– Continental crust- sial
• Less dense and thicker than oceanic crust
– Oceanic crust- sima
– Mohorovicic discontinuity
CRUST
• 5 to 70 Km thick
• Oceanic Crust-SIMA
– thin (around 7 Km thick)
– basaltic – mafic rock
– P waves travel + 7 Km/Sec
• Continental Crust-SIAL
– Thick- especially under mountains
– granitic- silicic rock
– P waves travel + 6 Km/Sec
• “Moho” (Mohorovicic Discontinuity)
– Boundary between Crust and Mantle
Mantle
• P-wave velocity 8 Km/sec & higher
• Made of ultramafic rock
– Low in silica, high in Fe, Mg
– Denser than basalt
• Lithosphere
– rigid uppermost part of mantle plus crust
– tectonic plates
– Average thickness of 100 Km.
• Asthenosphere
– soft upper part of mantle
CORE
• P-wave shadow zone
• S-wave shadow zone
• Outer Core- liquid
• Inner Core- solid
• believed to be mostly iron
– with some nickel
– Overall Density of earth = 5.5
• Crust 2.7-3.0
• Upper Mantle 3.3
• Mantle is 85% of volume of earth
• Fe at core boundary around 10.0
• at center is around 13.0
– Evidence from meteoritesGRAVITY
• Equilibrium
– Isostasy & Isostatic adjustment
• Crust “floating” on mantle
Gravity measurements
• Equation for force of gravity
• Gravity meters
• Variations of G
– Anomaly
• Positive
– Greater G
– “Held up” crust
• Negative
– Less than normal G
– “pulled down”
Earth’s Magnetic Field
• Magnetic Field
– Generated in core
• Magnetic Poles
– Dipolar
• Magnetic Reversals
– Normal & reversed polarity
– Curie Point
– Paleomagnetism
• Record of magnetic reversals
• Magnetic Anomalies
– Magnetometer
– Positive/ Negative Magnetic Anomalies