Transcript Mass Wasting
17.2 Notes: Earth’s Magnetism
Main Points:
All magnets have a north & a south pole. Opposite poles attract.
N S 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.
M-N 20 degrees 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
Solid Inner Core:
Outer Core
Composition: IRON!
Composition: IRON & Nickel!
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.