A Layered Earth•Solid inner core- 6,370 km deep

•Liquid outer core- 2,900 km deep

•Mantle – 100-200 km deep

•Brittle crust- Surface to 100-200 km

Evidence from Earthquakes

• Two Types of Seismic Waves– P Waves: Compressional– S Waves: Transverse

• Seismic waves do not travel at the same speed through the earth

• S Waves cannot pass through liquid– Shadow zone develops behind the liquid core

• P Waves slow down through liquid

Lithosphere and Asthenosphere

• Lithosphere (litho=rock)– 100-200 km thick– Oceanic and Continental Crust

• Asthenosphere (asthenes=week)– Below Lithosphere to 350-650 km– Hot, partially liquid upper part of the Mantle

Continents

• Continents are made of low density crust rock (like granite) that floats on denser crust

• Oceanic crust is more dense than continental crust so it sits lower

Continental Drift

• Continents look like they fit together– S. America and Africa

• 1912-Alfred Wegener proposes that continents move. – Everyone thought he was nuts

• 1960- Seafloor spreading