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Unit 8 Lesson 1 Weathering
Ms. Grant
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
Florida Benchmarks
• SC.6.E.6.1 Describe and give examples of ways in
which Earth’s surface is built up and torn down by
physical and chemical weathering, erosion, and
deposition.
• LA.6.2.2.3 The student will organize information
to show understanding (e.g., representing main
ideas within text through charting, mapping,
paraphrasing, summarizing, or
comparing/contrasting).
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
Break It Down
What is weathering?
Weathering is the breakdown of rock material by
physical and chemical processes.
Two kinds of weathering are physical weathering
and chemical weathering.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
What causes physical weathering?
Physical weathering is the process by which
rock is broken down into smaller pieces by
physical changes.
• The composition of the material does not change
during physical weathering. What does that
mean?
Agents of physical weathering include temperature
changes, pressure changes, plant and animal
actions, water, wind, and gravity.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
What causes physical weathering?
• Changes in temperature can cause a rock to break
apart by weakening the structure of the rock.
• Heat causes expansion.
• Cold causes contraction.
Ice wedging, or frost wedging, causes cracks in
rocks to widen with repeated cycles of freezing
and thawing.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
What causes physical weathering?
• How can a small crack in a rock eventually split
the rock into two or more pieces?
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
What causes physical weathering?
• Rocks that formed under deep pressure can be
exposed to the surface.
• Pressure changes can cause the rock to expand as
material is removed above the rock.
• Exfoliation is the process by which the outer
layers of rock slowly peel away due to pressure
changes.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
What causes physical weathering?
• Animals can cause physical weathering by digging
burrows.
• New rock material and soils become exposed to
the surface as a result of animal actions.
The main causes of crack growth in rocks over
time is plant roots and ice wedging
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
What causes physical weathering?
Abrasion is the breaking down and wearing away
of rock material by the mechanical action of other
rocks.
Three agents of physical weathering that can
cause abrasion are moving water, wind, and
gravity.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
What causes physical weathering?
• Roots of plants can grow in a small crack in a
rock, causing it to be wedged apart over time.
• As roots grow, more pressure is put on rock,
causing expansion.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
Reaction
What causes chemical weathering?
Chemical weathering is the breakdown of rocks
by chemical reactions.
Chemical weathering changes both the
composition and appearance of rocks.
Agents of chemical weathering include oxygen in
the air and acids.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
What causes chemical weathering?
Oxidation is the process by which other
chemicals in rock combine with oxygen in the air.
• Rock surfaces can change color during oxidation,
indicating a chemical reaction may have occurred.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
What causes chemical weathering?
• Acids can cause chemical weathering by breaking
down minerals faster than water alone.
• Acids in the atmosphere are created when
chemicals combine with water in the air.
Acid precipitation occurs when strong acids fall
to Earth as rain, sleet, or snow.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
What causes chemical weathering?
Water in the ground can cause chemical
weathering.
Acids in groundwater can cause rock to dissolve.
• Dissolved chemicals in groundwater can be
deposited in new locations over time.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 1 Weathering
What causes chemical weathering?
• Acids in living things can cause chemical
weathering.
• Chemical reactions occur as acids produced
naturally by living things move through rock
material.
• Acids can break down rocks.
Copyright © Houghton Mifflin Harcourt Publishing Company

So, how does weathering change Earth’s
surface?
The End