Earth’s Interior
How do we know the structure of Earth?
l Average density
of Earth (________________ gm/cm3)
»
Denser
than crust and mantle
l Rocks with
minerals that form at high temperatures and pressure (e.g., kimberlites)
l Composition of
meteorites
l Seismic wave
velocities
l Laboratory
experiments
»
Chemical
stability
l Earth’s magnetic
field
The Crust
l Ocean Crust
» 3-15 km thick
» Basaltic rock
– Young (≤180
Ma)
» Density ≈
3.0 g/cm3
l Continental Crust
» 35 km average
thickness
» _____________________
rock
– Old (up to 4
billion years)
» Density ≈
2.7 g/cm3
The Mantle
l ~2900 km thick
»
Comprises
>_______% of Earth’s volume
l Mg-Fe silicates
(rock)
»
Density
= 3.3 g/cm3
l Two main
subdivisions:
»
Upper
mantle (upper 660 km)
»
Lower
mantle (660 to ~2900 km; “Mesosphere”)
Mantle and Crust
Lithosphere/Asthenosphere
l Outer 660 km
divided into two layers based on mechanical properties (Fig. 1.14)
l _______________________________
»
Rigid
outer layer including crust and upper mantle
»
Averages
100 km thick; thicker under continents
l ______________________________--
»
Weak,
ductile layer under lithosphere
»
Lower
boundary about 660 km (entirely within mantle
The Core
l Outer Core
»
~2300
km thick
»
___________________
Fe with Ni, S, O, and/or Si
»
Magnetic
field is evidence of flow
»
Density
≈ 11 g/cm3
l Inner Core
»
~1200
km thick
»
___________________
Fe with Ni, S, O, and/or Si
»
Density ≈ 13.5 g/cm3