Earth’s Interior

Evidence for the structure of Earth’s interior is indirect P and S seismic waves provide evidence of a multi-layered interior with each section possessing distinct properties Density and gravity studies of Earth and its influence on other celestial bodies requires an interior more dense than the crust Meteorite samples provide material evidence for the composition of Earth’s interior

Seismic waves (P & S) increase in velocity at depth of 10 to 30 km (varies locally) This is the boundary between the crust and mantle Density increases abruptly The boundary is called the Mohorovicic Discontinuity

You can call it the MOHO

P and S waves

P and S wave shadow zone No seismic waves are received in a zone on the other side of Earth from the Focus ( 102-143 degrees )

P waves only are received at an angle greater than 143 degrees from the focus

P waves are deflected as they travel through a new medium - the liquid outer core

S waves do not travel through liquids

Outer core is liquid inner core is solid

Isaac Newton Observed Earth’s gravitational influence on other celestial bodies If Earth is to have enough mass to exert that much gravity, it’s interior must be more dense than the crust Several minerals are possible

Properties of Earth’s interior Must be dense Must contain liquid to stop S waves Must be metallic to create magnetic field when rotating

Meteors contain elements from early solar system and formation of planets Meteors contain heavy elements iron and nickel Iron and nickel are dense enough and exist as a liquid at pressures and temperatures inferred for Earth’s core

Inferred properties of Earth’s interior

Summary Earth has very thin crust which fractures easily Mantle is below the crust and is much more dense Outer core is a viscous liquid and is made of iron and nickel Earth has a solid iron-nickel inner core Density, temp, and pressure all increase from the crust to the inner core

Temp and pressure increase with depth

The End