17.2 Notes: Earth’s Magnetism

1. Main Points: All magnets have a north & a south pole. Opposite poles attract. Like poles repel each other (ie south repels south, north repels north). 17.2Notes: Earth’s Magnetism N S S S Types: Permanent magnets & electromagnets

2. Electromagnet: Can only display magnetism when there is an electric current source. They are found in motors, hard drives, and tons of other devices.

3. Permanent Magnet: The magnetic field is generated and maintained by the internal structure of the material itself.

4. Earth’s Magnetosphere Magnetic Field Lines: These allow you to figure out which way a magnet will align. Lines exit south pole & enter at north pole. Describe:

5. It’s not the permanent geographic north pole! It shifts about 10km/year. Magnetic North Pole Main Points

6. The angle of difference between the geographic (G-N) & magnetic north (M-N) poles. Declination G-N 20 degrees Define M-N

7. The poles REVERSE approx every 250,000 years. Last reversal was more than twice as long: about 740,000 yrs ago! Pole Reversals If you were alive about 800,000 years ago, and facing what we call north with a magnetic compass in your hand, the needle would point to 'south.' Length of Cycle

8. Areas where crust is actively being formed at mid-oceanic ridges. Ocean floor evidence of Pole Reversals Location:

9. Lava pushes its way up thru seafloor & cools & solidifies. This reveals the alignment of magnetic minerals w/in the sea floor. Scientists can see a banding pattern. Young rocks are nearer the ridge, older Rocks are further away. This banding also reveals pole reversals that have occurred. Describe: Location:

10. Solid Inner Core: Composition: IRON & Nickel! Motion: Constantly moving in convection cells around the inner core! Earth’s Liquid Outer Core Composition: IRON!

11. The liquid outer core swirls around the inner core. Iron in the outer core acts as a conductor & creates a magnetic field. Describe Theory