What Do We Know About the Inside of Our Earth?

Core• No direct samples• Probably heavy stuff• Inner core

– Solid– Density of pure iron or

nickel/iron– ~ 12-13 g/cm3

– ~ size of moon• Outer core

– Molten (does not transmit S-waves)

– Includes ~ half of diameter of Earth

– ~ 10-12 g/cm3

– Core-mantle boundary (Gutenberg Discontinuity) is largest density contrast in Earth

Mantle

• Density – between crust and core• 3.3 - 5.5 g/cm3

• Probably material such as peridotite (lots of heavy olivine - Fe, Mg)

• Samples from kimberlites, xenoliths in volcanic eruptions, basalt composition; lab experiments

• MOHO - Mohorovicic Discontinuity • Core mantle boundary - change in

mineralogy

Crust

Our deepest hole: 12 KM ….. we have a long way to go!

• Two types of crust:– Continental

• 30% of crust• Granites and Diorites - rich in

silicates and feldspars (lighter

materials)• 40 Km thick• Oldest is 3.8 billion years

(90% solar system age; missing ~700

m.y.)

– Oceanic crust• Basalt - Mg, Fe (heavier

materials)• 5-10 Km thick• 200 Ma oldest; 100 Ma

average