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Chapter 8
Earth’s Core
• Lithosphere- solid outer crust of Earth
– Rock and hot plastic-like upper mantle
• Three major parts or layers:
– Earth’s core:
• Outer liquid portion
• Inner solid portion
• Composition believed to be iron and nickel
Earth’s Core (continued)
• 1,800 miles to outer core
• 1,300 miles to inner core
• Core is extremely hot
– 8,000 F
• Used seismic waves to reveal composition
• Impossible to observe directly
• Makes up most of Earth’s volume
• Composed of hot solid material
– Silicon, oxygen, iron, aluminum, and magnesium
– 1,800 miles think and extremely high pressure
– Heat moves upward through mantle
• Forms convection cells
• Extreme heat comes from:
– Radioactive decay
– Friction
– Residual heat
• Upper mantle called the asthenosphere
– Flows like thick syrup
• Outer portion is composed of solid rock
• Thickness from 40 miles to 3 miles
– 40 miles under mountains
• Continental crust- density 2.7 gm/cc
– 3 miles under parts of the ocean
• Oceanic crust- density 3gm/cc
• Denser because of pressure of ocean
• Oceanic crust made of basalt
• Earth floats on top of upper mantle
– Like a cracker floating on soup
• Seven elements make up 99 percent of crust
– Oxygen and silicon form 72 percent of the crust
– Aluminum, iron, calcium, magnesium, sodium
form the remainder
• Lower crust and upper mantle form the
asthenosphere
• Model developed using seismic waves
• Also studied inner composition of meteorites
– Helps in understanding Earth’s interior
• Deepest penetration by drilling is 9 miles
• Deepest mine is slightly over 2 miles
• Model is constructed by inference
• Inference- conclusion based on gathered
evidence
• Can only infer because can’t travel there
• Many theories based on inference
– Earth is so large
– Much cannot be studied by direct observation
• Oceans
• Atmosphere
Earth’s Interior