Unit 4
Lesson 1
Processes that Change
Earth’s Surface
S8.D.1.1.1,2,4
1
Weathering
•
Breakdown of rocks into smaller pieces
called sediment
•
•
3 main causes of weathering
1. Liquid water
2. Ice
3. Wind
2 kinds of weathering
1. Physical Weathering
2. Chemical Weathering
2
Physical Weathering
• rock breaks into smaller pieces but its
chemical composition does not change
• Also called Mechanical weathering
Unloading/
pressure release
3
Chemical Weathering
• The chemical composition of the rock changes
• Rocks break down through chemical reactions
• Air and water react with minerals in rock to
create various chemical reactions
Feldspar to Clay
4
Erosion
• Process by which sediment is moved over
Earth’s surface by water, wind, or ice
Houses undermined by
coastal erosion in Pacifica,
California. Photograph
courtesy of NASA.
5
Erosion
• Most erosion happens over long periods
of time
• rivers carving through land takes millions of years
The Grand Canyon is
an impressive example
of stream erosion
through rock
Erosion clip
6
Erosion
• Some erosion happens very quickly
• after heavy rains, fast moving
water can carry large amounts
of sediment away
• heavy rains can also cause
landslides
• Soil erosion can be prevented by planting vegetation, trees,
shrubs, and other plants.
• Roots of these plants will help hold soil in place. Soil will not be
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blown away by wind or washed away by water as easily
Deposition/Sedimentation
• Process in which eroded sediment is
dropped at another location
• Sediment may get transported
thousands of miles by one of the
world's major rivers, or it may just
go from the top of the hill to the
bottom during a landslide
*Increase erosion somewhere can cause an increase
of sediment elsewhere
8
Deposition/Sedimentation
• Most deposition happens when water or
wind slow down
9
Formation of Mountains
• When two of earth’s plates collide, mountains can form
• The formation of mountains takes millions of years
Appalachian Mountains
Video clip of
mountains forming
Pocono Mountains
10
3 Types of Rocks
1. Sedimentary
2. Igneous
3. Metamorphic
11
Sedimentary Rocks
•
Form from:
1. Sediment
2. Remains of living things (coal)
• Sediment builds up and top layers put pressure
on bottom layers squeezing the sediment together
• Over time, sediment in lower layers become
cemented together to form sedimentary rock
12
Sedimentary Rocks
Sandstone
Limestone
Shale
Coal
13
Igneous Rocks
• Magma- molten rock underground
• Lava- molten rock above ground
• Igneous rock forms when molten rock
cools and hardens
– If it cools slowly, large crystals form
– If it cools quickly, small crystals form (obsidian)
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Igneous Rocks
Granite
Pumice
15
Metamorphic Rocks
• Form when heat and pressure change the chemical
composition of a rock
• Rocks that are buried very deep are under
extreme heat and pressures
• Minerals in the rock react to form new minerals
• Most metamorphic rocks in Pennsylvania formed
from the continental collision responsible for the
formation of the Appalachian Mountains
16
Metamorphic Rocks
Slate
Forms from shale
Forms from sandstone
Marble
Gneiss (nice)
17
Forms from limestone
Form from granite
Rock Cycle
•Rocks can cycle between types if exposed to:
•heat and pressure
•weathering and erosion
•melting and cooling
18
Rock Cycle
Rock Cycle
Animation
19
Fossils
• Evidence that organisms existed in the distant past
• Can help scientists learn what ancient organisms
– looked like
– where they lived
– when they became extinct
• Can also help scientists learn about Earth’s
environments in the past.
•Ex. Finding a marine fossil somewhere would suggest that area
was once underwater
• Estimated that one in a million organisms become a
fossil
20
Trilobite
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