Date
Name
Class
Rocks and Weathering
Guide for
Reading
a Whatcauses
mechanical
weathering?
a Whatcauses
chemical
weathering?
<)Whatdetermines
howfast
weathering
occurs?
42c G
eathering is the process that breaks down rock and other
materialsat Earth'ssurface.The forcesof weatheringbreak rocks
into smallerand smallerpieces.The forcesof erosioncarry the pieces
away.Erosion is the movementof rock particlesby wind, water,or ice.
Weatheringand erosionwork togethercontinuouslyto wear down and
cafiy awaythe rocksat Earth'ssurface,
The type of weatheringin which rock is physicallybroken into smaller
piecesis calledmechanical weathering. Thesesmallerpieceshave the
samecompositionas the rock they camefrom. Mechanical weathering
breaks rock into piecesby freezing and thawing, heating and cooling,
growth of plants, actions of animals, and abrasion. In cool climates,
the most important force of mechanicalweatheringis freezingand
and actsasa wedge.This process
thawing.Waterexpandswhen it freezes,
is calledice wedging. Heatingand coolingcan causerocksto crack.Plant
roots can pry apart crackedrocks.Rock particlescarriedby wind, water,
and ice can wear away rocks in the processcalled abrasion. Animal
actions,suchasburrowing,can breakapart rocksin the soil.
Chemical weathering is the processthat breaksdown rock through
chemical changes.The agents of chemical weathering include rrater,
oxygen, carbon dioxide, living organisms, and acid rain. Chemical
weatheringproducesrock particlesthat havea differentmineral makeup
from the original rock. Chemicaland mechanicalweatheringoften work
together.As mechanicalweatheringbreaksrock into pieces,more surface
areabecomesexposedto chemicalweathering.
Water is the most important agent of chemical weathering.Water
weathersrock by dissolvingit. The oxygenin air is an important causeof
chemical weathering.Iron combines with oxygen in the presenceof
water in a processcalledoxidation.Rock that containsiron oxidizes,or
rusts.Another gasfound in air, carbondioxide,combineswith rainwater
to form carbonic acid. Carbonic acid easily weathersmarble and
limestone.Plant roots produceweak acidsthat slowly dissolveany rock
around the roots.Lichensalsoproducea weakacid that weathersrock.
Acid rain causes
very rapid chemicalweathering.
The most important factors that determine the rate at which
weathering occurs are tnre of rock and climate. Some types of rock
weather more rapidly than others. For example,limestoneweathers
easilybecauseit is permeable, which meansthat it is full of air spaces
that allow water to seepthrough it. Both chemicaland mechanical
weatheringoccur fasterin wet climates.Chemicalweatheringoccurs
more quickly wherethe climate is both hot and wet.
TeachingResources
Earth'sChangingSurface
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Name
Date
Class
Rocks and Weathering
I Understanding Main ldeas
Fill in the blanksin the tablebelow.
Agent
Type
Description
I
Mechanical
Rock particleswear awayrock
2.
Chemical
Formsfrom coal,oil, and gasburning
Freezingand thawing
3.
Breaksrock by ice wedging
Carbon dioxide
4.
Formscarbonicacid in water
f,.
Chemical
Weathersmarble and limestone
6.
Mechanical
Burrowingin the groundbreaksrock
Plantgrowth
7.
Rootspry apart cracksin rock
Living organisms
8.
Produceweak acid that weathersrock
Oxygen
9.
Causesrust on somerock
10.
Mechanical
Sun or forestfire causesrock to crack
Answerthefollowing questionson a separatesheetof paper.
ll. How doeserosiondiffer from weathering?
12. What factorsdeterminethe rate of weathering?
s
j
f Building Vocabulary
G
Fill in the blank to completeeachstatement.
o
.o
13.
is the movementof rock particlesby wind, water,or ice.
14.
meansthat a materialhasspacesthat allow water to seep
-
q)
oA
through it.
15.The processthat breaksdown rock and other materialsat Earth'ssurfaceis
called
16. The grinding awayof rock by other rock particlesis called
17.The processby which ice widensand deepenscracksin rocksis called
Earth'sChangingSurface
T e a c h i n gR e s o u r c e sG . 4 3