magnetic field
Earth’s field reverses every 106 y
- seen in record of new crust at mid-Atlantic ridge
- Sun’s field reverses every 22 y
- recall 11 y sunspot cycle
Probing Earth’s interior
- Use Earthquakes = seismic waves
- 2 types
- P -- pressure -- longitudinal -- sound wave
- S -- “sidewise” -- transverse -- like light wave demo
- S-waves can’t travel through liquid
- shadow zone => liquid core S65
- liquid Fe gives strong magnetic field!
- innermost core solid Fe (higher pressure)
- seismic waves are used to study
- interior of Sun (helioseismology)
- interior of Moon