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Changes to the Earth’s surface
The changing Earth
• The surface of the Earth
is always changing.
The Rock cycle
• The rock cycle shows
how rocks change back
and forth between
sedimentary, igneous,
and metamorphic rocks.
The rock cycle - Igneous
• Igneous rocks form when
melted rock cools and
solidifies.
• The crystal size in an igneous
rock is determined by how fast
the rock cooled.
• How fast the rock cooled is
determined by how close to
the surface the rock was, and
how large the chamber was.
• Igneous rocks can be extrusive
or intrusive
The rock cycle - Igneous
• Examples of igneous
rocks include:
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Obsidian
Granite
Basalt
Pumice
Rhyolite
The rock cycle – Sedimentary
• Sedimentary rocks are
formed by weathering,
erosion, deposition,
compaction, and
cementation of other
rocks.
The rock cycle – Sedimentary
• Examples of
sedimentary rocks
include:
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Sandstone
Limestone
Flint
Shale
Coal
Limestone
The rock cycle – metamorphic
• Metamorphic rocks
form when heat and
pressure deep beneath
earth’s surface cause
one type of rock to
change into another
type of rock.
The rock cycle – metamorphic
• Examples of
metamorphic rocks
include:
– Gneiss (from Granite)
– Quartzite (from
Sandstone)
– Schist
– Slate (from Shale)
– Marble (from Limestone)
Energy in the rock cycle
• What types of energy
are needed to form
each type of rock?
– Igneous
– metamorphic
– Sedimentary
Rock cycle
• Heat energy is
important in the
formation of igneous
and metamorphic rocks.
• Where does that heat
come from?
Heat energy
• The earth gets hotter
the deeper down you
go, but why?
– Radioactive decay
Kinetic energy
• Some of the heat
energy in the mantle is
transformed into kinetic
energy in the form of
convection currents
that form in the mantle.
Kinetic energy
• Convection
currents move
the plates of
the crust back
and forth.
• A place where
2 plates meet
is called a
fault.
Kinetic energy  Potential energy
• Kinetic energy of the
moving plates can be
converted into potential
energy when two plates
collide and “stick”
together.
• The potential energy
builds up until it is
finally converted back
into kinetic energy and
the plates “slip”
Plate boundaries
• Plates that pull apart are
called divergent plates
• Plates that push together
are called convergent
plates
• Plates that slide past each
other are called transform
plates.
• What do you think would
happen to the earth at
each type of boundary?
Plate movement
• As plates slide over,
under, or past each
other, they change
the surface of the
earth.
Plate movement
• Plates that push
together can cause
the earth to
“crumple” and
form mountains.
Plate movement
• When
continental and
oceanic plates
collide, they can
produce
volcanoes.
Plate movement
• When plates “slip”,
“smash” or “pull” apart
they produce earthquakes.
• During an earthquake,
potential energy is
converted to kinetic
energy.
• (Remember that this
mechanical energy started
as heat energy inside the
earth.)
Plate movement
• Some of the heat energy
from the earth reaches the
surface (as in a volcano.)
• Some heat energy is
transformed into mechanical
energy in the form of
convection currents, moving
plates, earthquake waves,
flowing lava, etc…
Energy  to infinity and beyond!
• Earthquakes, volcanoes,
and mountain
formation all occur
when the heat energy
from inside the earth
makes its way to the
surface. (Either as heat
energy or mechanical
energy.)
Energy  to infinity and beyond!
• Earthquakes and volcanoes
can change earths surface
very rapidly.
• Mountains building is a slow
and gradual process that
changes earths surface.
• These changes all occur
because energy from earths
interior transfers to the
earth’s surface.
Changes to Earth’s surface
• Some changes to the
Earth’s surface are not
caused by energy from
the interior of the
earth.
• These changes can
come from weathering,
erosion, deposition,
gravity, glaciers, and
other “agents” of
change.
Weathering
• Weathering occurs
when rock on the
surface of the earth
breaks down into
smaller pieces.
• Weathering can be
mechanical or chemical.
Mechanical Weathering
• Mechanical weathering
is when mechanical
energy creates
weathering. This
mechanical energy
could come from:
– Moving water/wind
(abrasion)
– Freezing ice
– Burrowing animals
– Growing plant roots
Chemical weathering
• Chemical weathering
occurs when chemical
energy causes weathering
to occur.
• Things that could cause
chemical weathering
include:
– Acid rain
– Oxygen (oxidation)
– Living things making acids
to break down rock. (like
lichens)
Erosion and deposition
• Erosion occurs when
water, wind, or ice
move weathered rock
particles from one place
to another.
• Deposition is when
those particles being
carried by erosion get
laid down somewhere.
Weathering, erosion, and
deposition
• Weathering, erosion, and deposition are
important parts in the process of soil formation.
Gravity
• Gravity changes the
surface of the earth.
Particles that weather
and erode in the
mountains get carried
to the valleys.
• Gravity moves particles
and sediment downhill.
Gravity
• Gravity can cause
several types of “mass
movement” downhill
including:
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Landslide
Mudflow
Slump
Creep
Gravity – Mass movement
• Landslides occur when
rock and soil move
quickly down a slope
• Mudflows occur when
water, rock, and soil
move downhill.
(Usually during heavy
rain.)
Gravity – Mass movement
• Slumps occur when an
entire section of a
hillside suddenly slides
down a slope but stays
together.
• Creeps occur when rock
and soil moves downhill
very slowly.
Glaciers
• Glaciers move slowly
across the land. As they
move, they shape the
land in many ways.
Glaciers
• Glaciers create features
in the earth such as:
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U-shaped valleys
Cirques
Horns
Drumlins
Weathering Erosion and
Deposition
• Weathering, erosion
deposition and gravity
can change the surface
of the earth gradually or
rapidly.
Rapid change
• Flash floods, landslides,
mudflows, earthquakes,
volcanoes can all
change the earth
rapidly.
Gradual change
• Mountain formation,
mountain destruction,
weathering, erosion,
creep, and glacial
activity are all gradual
changes to earth’s
surface.
Mountain building
• The average mountain
that is actively being
built is moving upward
at a rate of 6 mm/year
and being eroded
downward at a rate of 1
mm/year.
• A mountain that takes 5
million years to build
might take 100 million
years to erode away.
Mountain building
• As a mountain erodes
away, the roots of the
mountain push upward.
• For every 5 mm of the
mountain that erode
away, the roots push up
4 mm.
• The taller the mountain,
the faster erosion
occurs.