Layers of Earth

Vocabulary

For two-column notes, underlined titles are main ideas

Showing the Layers of EarthThere 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

Oceanic crust

Continental crust

Mantle

Crust

Draw this diagram. Leave room to label the parts of the mantle and core

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

Lithosphere crust and hard part of

upper mantleAsthenosphere: below lithosphere

Lower 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 outer core

The inner 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 zoneFrom 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 poles the circumference is 40,007 km

Measured around the equator the

circumference is 40,074 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

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?

Copy the questions into your notebook (right-side) and answer them