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Layers of Earth
Vocabulary
For two-column notes, underlined titles are main ideas
Showing the Layers of Earth
There are four layers of the Earth. Draw this
diagram
Properties of Layers of Earth
•
•
•
Size
Composition
Temperature
– Temperature increases with depth
•
Pressure
– As you go deeper, the weight or rocks
above increases
– Pressure depends on the weight of rock
above
– So pressure increases with depth
Layers of the Earth
•
Crust
– Layer of solid rock 200°C to 400 °C that
includes both dry land and ocean floor
– 5-70 km thick
– Continental crust (30-70 km)
• Under continents
• Composition - made of many types of rock, but
mainly like granite
– Oceanic crust (5-10 km)
• Under oceans
• Composition mainly like basalt
• Thickness of oceanic crust less than continental
– Both types "float" on the mantle
Layers of the Earth
•
Oceanic crust - diagram
Draw this diagram. Leave room to label the parts of the mantle and
core
Continental crust
Oceanic crust
Mantle
Crust
Layers of the Earth
•
Mantle
– Makes up 2/3 of Earth's mass
– Layer of hot (500 °C to 4,000 °C) but solid
rock
– Almost 3000 km thick
– Divided into two parts
• Upper mantle - Crust to 660 km
– Rigid top plus crust form lithosphere (<200 km)
– Asthenosphere just below lithosphere is “plastic”
– Plastic means that a solid is able to flow
• Lower mantle – 660 km - 2891 km
Asthenosphere:
below lithosphere
Lower
mantle
Lithosphere crust
and hard part of
upper mantle
Layers of the Earth
•
Core
– Occupies center of planet
– Almost 1/3 of Earth’s mass
• Outer core - 4,030°C to 5400°C
– 2258 km thick (3400 km radius)
– Dense liquid nickel-iron
• Inner core - 5400 °C
– Radius of 1222 km
– Solid iron
– Would be liquid except for great pressure preventing
atoms from spreading out
The inner core
The outer core
How we know about the Earth’s structure
• No one has been to the center of the Earth
• We use information gathered from seismic waves
(produced by earthquakes) to learn about the core of the
Earth
P-Wave shadow zone
From the lack of S
waves (which can’t pass
through liquids) and a
great slowing of the P
wave velocity (by about
40%) it was deduced
that the outer core is
made of liquid. The
shadow zone also
defined the diameter of
the core.
Earth as a magnet
• The source of the Earth’s
magnetic field may be the
liquid iron outer core. Iron is a
good electric conductor.
• The Earth’s magnetic field
extends beyond the Earth
The region of space affected by Earth’s
magnetic field is the Magnetosphere
Earth as a magnet
• Magnetic versus geographic poles
– The geographic poles of the Earth are located
where the axis of rotation intersects the planet
– The magnetic poles of the Earth are near the
geographic poles
– The magnetic poles wander over time
– They also reverse from time to time (about every
70,000 years)
– Note that the magnetic South Pole is in the
Northern Hemisphere and the magnetic North Pole
is in the Southern Hemisphere
Shape of the Earth
• The Earth is not a perfect sphere.
• We know this by looking at the
circumference (length around
something round).
Measured
around the
equator the
circumference is
40,074 km
Measured
around the
poles the
circumference
is 40,007 km
Shape of the Earth
• The Earth is an oblate spheroid (slightly
squished sphere)
• The spinning of the Earth on it’s axis
causes the polar regions to flatten and the
equatorial area to bulge.
• The Earth is mostly smooth: the difference
between the height of the tallest mountain
and the deepest sea trench is only about
20 km.
Classwork 1 – Layers of Earth
Copy the questions into your notebook (right-side) and answer them
1. What part of the Earth’s core may be
responsible for its magnetic field?
2. Name the three parts of the mantle and
describe each
3. Where is the Earth’s South magnetic pole
really located?
4. What part of the mantle is a plastic solid?
5. Which is thicker, the continental or oceanic
crust?
6. What shape is the Earth?