Transcript Earth structure & magnetism

Earth Science
A study in Change: Earth
Structure & Magnetism
Review
• Know that the earth is not static.
 It changes!
 Natural resources unit: environment, oil, etc.
 Rocks that appear to always be the same go
through a cycle.
 Igneous, Sedimentary, Metamorphic
• What drives this cycle? How does it work?
 Plate tectonics
 Earth structure
Earth’s Basic Structure
• Crust: outermost layer, 8-75 km thick
 Oceanic - thin, more dense, younger
 Continental - thick, less dense, older
• Mantle: middle layer, 82% of Earth’s
volume, 2890 km deep
• Core: innermost layer, composed mostly of
iron (magnetic!) & nickel.
Earth’s Structure In Detail
1. Lithosphere = Crust (upper mantle): solid,
floats on the asthenosphere, 100 km thick
2. Asthenosphere = Upper Mantle: warm butter
solid
3. Lower Mantle: liquid
4. Outer core: liquid, flow causes the magnetic
field of the Earth
5. Inner core: solid
• Very important to understanding why & how
plate tectonics works!
Earth Structure(pp.234-235)
Solid
Liquid
Solid-ish
Solid
Liquid
Earth Structure Characteristics
• Pressure
 Increases with depth
 The closer you are to the center of the Earth, the
more rock is piled on top of you
• Temperature
 Increases with depth (related to pressure)
 Liquefies rock
 Core is a solid because there is so much pressure,
the rock can only exist as a solid.
So What?
• Recall: Temperature and density are related!
 Warmer substances increase volume while mass
remains constant
 In other words, molecules move faster and spread out.
 DECREASES DENSITY! = hot substances rise/float
• Hotter rock near the center will rise and cool as it
nears the surface.
 Convection currents within the Earth
• Sets up a driving force for plate tectonics.
Convection Currents (pg. 270)
Core and Magnetic Field
• Earth acts like a large bar magnet
• Outer core = major component is iron,
flowing liquid
• Gives us magnetic North
 What makes your compass work
 What protects us from excess solar energy
 Helps position satellites
Drawing of field lines
Earth’s magnetic field
So what?
• So what? When liquid rock on/in the crust cools,
iron containing minerals will line up with the
magnetic field lines of the earth.
 Parallel to Earth magnetic field lines.
 Just like the the metal pieces on the demo
• These rocks are like a recording of a
conversation. . .
 They are an account of the magnetic polarity of the
earth (which way is north/south)
 They are an account of the location of the rock during
its formation. (has it been moved since?)
• Called paleomagnetism
Paleomagnetism
• Every so often the magnetic field will
reverse.
• When it does, so will the minerals in the
igneous rocks that form at the time.
 Stacked lava flows (layers)
 Rocks at places where new crust is forming
(Sea floor spreading = stripes)
Reversal Model
• Reversal begins at
the core
• As the core becomes
more disorganized, so
does the magnetic
field at the surface.
• Field is weakened as
“islands” form, current
= South Atlantic
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Paleomagnetism (pg 265)
Importance of Magnetic field
• Provides protection from solar wind,
radiation, and X-ray emissions from the
sun.
• Acts like a “force field” or “shield”
• (Movie clip)
Magnetic field in Action
Solar wind
• Solar wind = release of high energy ions
from the outer layer of our star
 Minor = power grid and satellite problems,
migratory animals off course, aurora borealis.
 Major = voltage control problems (blackouts),
satellite problems(positioning and data), radio
and navigation issues, aurora borealis seen in
Florida and Texas.
Aurora Borealis, Alaska
Radiation
• Radiation = high energy particles given off
by the sun (50,000X energy of molecules
we breathe!)
 Minor = minor radio problems in polar regions
 Major = radiation risk to air crew and
passengers, satellites useless, blackout radio
conditions in polar regions, navigation errors.
X-Rays
• X-ray = wavelength of EM spectrum, disturbs the
ionosphere
 Minor = minor problems with HF radio on daytime
side, occasional loss of radio contact, low frequency
navigation signals weakened.
 Major = complete HF radio blackout on daytime side,
loss of contact with pilots and ship captains, loss of
navigation signals, satellite navigation errors may
spread to night side.
2001 Largest Flare in History
Salem Nuclear Power Plant