Transcript 27 - Cal State LA - Instructional Web Server

Planet Earth in Profile
The Layered Interior
Objectives
• Explore evidence that helps explain Earth’s
internal structure.
• Outline Earth’s internal layers and discuss some
of the evidence leading to their discovery
• Introduce the salient properties of Earth’s outer
layers, its crust and the underlying mantle
• Investigate the processes at work to modify
Earth’s surface, creating physical landscapes of
great diversity
Evidence of Earth’s Internal Structure
• Earthquakes
– Shaking and trembling of
Earth’s surface caused by
sudden release of stress within
the crust
• Seismic waves
– Surface waves
• Travel along the surface
– P-waves (primary waves)
• Back-and-forth; Compressional
• Travel trough liquids and solids
– S-waves (secondary waves
• Up-and-down; right angles
• Travel through solids only
Evidence of Earth’s Internal Structure
• Seismic Waves
– 0° to 103°
• Find P- and S-waves only
– 104°-142°
• Shadow zone
• No P-waves; bend due to
higher density of mantle
• No S-waves; cannot pass
through liquid
– 142°-180°
• Find P-waves only
• No S-waves; cannot pass
through liquid
Earth’s Internal Layers
•
Core
– Inner core
• Solid; Iron (Fe) and Nickel (Ni)
• 1220 km (760 mi) radius; 5150 km (3200 mi)
depth
– Outer core
• Liquid; Iron (Fe) and Nickel (Ni)
• 2250 km (1400 mi) thick; 2900 km (1800 mi)
depth
•
Mantle
– Lower mantle
• Solid; Iron (Fe), Magnesium (Mg), Silicon (Si)
• 2230 km (1385 mi)
– Upper mantle
• Solid-plastic-solid; Iron (Fe), Magnesium
(Mg), Silicon (Si)
• 670 km (415 mi) depth
[Insert Fig. 27.5 ]
Earth’s Outer Layer
• Mohorovicic discontinuity (Moho)
– The density has a marked different between the crust and mantle
• Earthquake waves speed up when passing from crust to mantle
• Indicates mantle is more dense than crust
– Made it possible to measure the thickness of the crust
• Thickness varies
• From 5 km (3 mi) to 40 km (25 mi)
Earth’s Outer Layer
• Crust
– Continental crust
• Felsic
– Feldspar rich (granitic)
• Light colored
• Low density (2.8 g/cm3)
[Insert Fig. 27.7A - felsic]
– Oceanic crust
• Mafic
– Magenisum (Mg) and iron (Fe)
rich (basaltic)
• Dark colored
• Higher density (3.0 g/cm3)
[Insert Fig. 27.7B - mafic ]
Earth’s Outer Layer
• Lithosphere
– Rigid layer
– Crust and uppermost
mantle
• Asthenosphere
– Plastic layer; flows readily
• Lithospheric Plates
– Large, rigid fragments
– Move over asthenosphere
Insert Fig. 27.8
The Crustal Surface
• Topographic Relief
– Vertical difference
between highest and
lowest elevation
– High relief
• Large difference from
high to low relief
– Low relief
• Small difference from
high to low relief
Insert Fig. 27.10 - low relief
The Crustal Surface
• Topographic Relief
– Vertical difference
between highest and
lowest elevation
– High relief
• Large difference from
high to low relief
– Low relief
• Small difference from
high to low relief
The Crustal Surface
• Continental Shields
– Large, stable, low relief expanse of land
– Old metamorphic, igneous rocks
• North American Shield
– Canadian (Laurentian) shield
The Crustal Surface
• Orogenic Belts
– Series of linear
mountains
– Zones of high relief
• Weathering
– Physical, chemical
breakdown of rocks
• Erosion
– Removal of weathered
rocks