Earth's Changing Surface

LESSON 1

THE CRUST

There are two kinds of crust

• Continental
• Oceanic

CONTINENTAL CRUST

• Makes up all the lands of the continents
• Is thickest in mountain areas
• Is mostly granite

OCEANIC CRUST

• Lies beneath most of the ocean floor
• Is made mostly of basalt
• Is not as thick as continental crust

THE CONTINENTAL SHELF

THE MANTLE

THE MANTLE

• The top part is solid hot rock
• Deeper in the Earth, the mantle is under very high pressure
• The temperature ranges from 360 to 2,500 degrees Celsius

THE MANTLE

• The rock here is solid but shares characteristics of liquid
• It can flow when acted upon by forces in the earth

THE MANTLE

• Flows in currents
• Cooler rock flows down
• Hotter rock flows up
• High temperatures inside Earth provide the energy for the currents to move

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THE CORE

THE CORE

• Has two parts: the inner layer and outer layer
• Is mostly made of iron
• The inner core is solid
• The outer core is liquid

THE OUTER CORE

• The liquid here flows in currents
• These currents make Earth's magnetic fields

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SCIENTISTS CAN'T GO TO THE CORE

CRACKS IN THE CRUST

EARTHQUAKES

THE SEISMOGRAPH

• Records earthquake waves
• The seismograph is firmly attached to a rock
• Earthquake vibrations cause the weights inside to move

Which of the Earth's layers is the thickest?

What kinds of problems would a scientist encounter trying to invent instruments to make direct observations of Earth's core?

LESSON 2

EARTH'S PLATES

EARTH'S PLATES

• The lithosphere is not a solid sheet of material
• It is broken into sections called plates

EARTH'S PLATES

• Several plates are larger than continents
• They are moving slowly
• Some as slow as 1 centimeter per year
• Some as fast as 24 centimeters per year

EARTH'S PLATES

• Movements cause big changes
• Mountains rise
• Valleys form
• The shape of the surface is caused by movement

WHY DO PLATES MOVE?

• Currents in the mantle push and pull on the plates
• Gravity pulls one plate under another

PLATE BOUNDARIES

CONVERGING

• Two plates collide
• Mountains are made when the crust folds, tilts and lifts

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DIVERGENT

• A spreading plate boundary forms when plates move apart from each other
• A low area between the plates forms called a Rift Valley

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TRANSFORM

• A sliding plate boundary that occurs when two plates move past each other in opposite directions

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LESSON 3

WEATHERING

• Weathering is a slow, destructive process that breaks rocks into smaller pieces
• The pieces are called sediments

THERE ARE TWO TYPES OF WEATHERING

MECHANICAL WEATHERING

• Mechanical weathering is the breaking of rock into smaller pieces by forces due to gravity, ice, plant roots, or other forces

ICE WEDGING

• When water freezes in the cracks of rocks, it expands and forces the rock to split
• This is called ice wedging

CHANGES IN PRESSURE

• When wind or water remove large amounts of dirt from a mountain side, the rocks are under less pressure
• The rocks then slowly expand at different rates

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MECHANICAL WEATHERING

• Mechanical weathering of different rocks occur at different rates
• The rate depends on the types of material in the rock and the conditions around it

EXAMPLE

• Plant roots grow in the cracks of rock and push the rock apart

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