Chapter 12 Earth’s Interior
Mount Etna, Italy
Earth’s Internal Structure Earth’s interior is divided into 3 major layers based on chemical composition Crust, Mantle & Core These layers are further divided based on physical properties
Layers of the Earth
Gravity and Layering The most dense material (iron) sinks to the center of the planet The least dense material makes up the outer layers
Seismic Waves & the Earth’s Interior We learn about the earth’s interior by studying seismic waves Velocities of P & S waves vary as they travel through the earth Travel faster through stiff (rigid) rocks
Possible Paths of Seismic Waves
The Earth’s Crust Oceanic Crust Forms at mid-ocean ridges Averages 7 kilometers thick Comprised of basalt and gabbro Average density of 3.0 g/cm3
The Earth’s Crust Continental Crust Lots of granite Averages 40 km thick Thickest ~70 km at mountains Thinnest ~20 km Basin & Range regions Average density of 2.7 g/cm3
The Mohorovicic Discontinuity The “Moho” is the boundary between the crust & mantle P wave velocities abruptly increase at the “Moho”
The Mantle ~80% of earth’s volume Solid rocky layer? Convection Cells Peridotite The “D” layer
The Core-Mantle Boundary (Guttenberg Discontinuity)
The Outer Core Is a liquid (absence of S waves) Density of 9.9 g/cm3 Mostly iron with some nickel
The Inner Core Is a solid Density of 13 g/cm3 Growing as the Earth cools Rotates faster than other layers
The Earth’s Temperature Heat flows from hotter to colder areas Earth’s core is 5500° C (10,000° F) Earth’s surface is 0° C (32° F) Heat flows from the core to the surface
How Did our Earth Get Hot? Accretion Radioactive Decay Asteroid collision Forming our moon
Types of Heat Transfer Conduction Convection Radiation Molecular Activity Convection Movement/Circulation Radiation Subatomic Movement
Mantle Convection & Plate Tectonics
Temperature Profile Geothermal Gradient Crust is 30° C/km Mantle is 0.3°C/km Except the “D” layer
Earth’s Magnetic Field Convection of iron in outer core Random reversals throughout history During reversals earth is unprotected
End of Chapter 12