Transcript Mass Wasting
17.2 Notes: Earth’s Magnetism Main Points: All magnets have a north & a south pole. S N Opposite poles attract. S S Like poles repel each other (ie south repels south, north repels north). Types: Permanent magnets & electromagnets Electromagnet: Can only display magnetism when there is an electric current source. They are found in motors, hard drives, and tons of other devices. Permanent Magnet: The magnetic field is generated and maintained by the internal structure of the material itself. Earth’s Magnetosphere Magnetic Field Lines: Describe: These allow you to figure out which way a magnet will align. Lines exit south pole & enter at north pole. Magnetic North Pole Main Points It’s not the permanent geographic north pole! It shifts about 10km/year. Declination Define The angle of difference between the geographic (G-N) & magnetic north (M-N) poles. 20 degrees M-N G-N Pole Reversals Length of Cycle The poles REVERSE approx every 250,000 years. Last reversal was more than twice as long: about 740,000 yrs ago! 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.' Ocean floor evidence of Pole Reversals Location: Areas where crust is actively being formed at mid-oceanic ridges. Describe: Location: 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. Earth’s Liquid Outer Core Solid Inner Core: Composition: IRON & Nickel! Composition: IRON! Motion: Constantly moving in convection cells around the inner core! Describe Theory The liquid outer core swirls around the inner core. Iron in the outer core acts as a conductor & creates a magnetic field.