Download green ch9 lesson4

LESSON GOALS
You will learn
• how igneous rocks
change.
• how sedimentary rocks
change.
• how metamorphic rocks
change.
rock cycle, the ways that
rocks change from one
form to another.
When the lava cools, it
will harden into igneous
rock.
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How Do Rocks Change?
The earth's crust is made of about twen
plates-pieces-of
rock that fit together like piec
of a puzzle. These plates move slowly over t
melted top of the mantle. The plates can bum
together, slide past each other, or spread apart.
When plates bump together, the edges of the plat
slowly crumple and fold, forming mountains. Whe
plates slide past each other, earthquakes happen. A
plates move, melted rock from inside the earth c
push up between the edges of the plates and form
volcano like the one below.
Sometimes these changes in the earth's cru
happen quickly. However, most of these change
happen slowly over millions of years. These change
cause new rocks to form and cause old rocks t
change. Like the earth's crust, rocks are alway
changing. The changes that rocks go through mak
up the rock cycle.
gneous Rocks
The moving plates that form the earth's crust are
ostly made of igneous rocks. These rocks form
irom magma, melted rock found deep inside the
arth. Magma changes to igneous rocks as it cools.
Some igneous rocks form inside the crust. These
cks form when magma flows into cracks in the
crust and cools slowly. You know that rocks are
ade of minerals. When magma cools slowly,
inerals in the magma often form large crystals.
otice the large quartz crystals and the crystals in the
~ anite. Both of these rocks formed when magma
cooled very slowly.
Some igneous rocks form outside the crust.
Pressure sometimes pushes magma out of the earth
ough a volcano. Magma that reaches the earth's
surface is called lava. The lava cools quickly on the
surface. When magma cools very quickly, minerals
the magma form very tiny crystals. How is the
asalt rock different from the granite?
_
igneous (ig/ne os) rock,
rock formed from cooled
magma.
crystal (kris/tl), a
substance made up of
atoms arranged in a
repeating pattern. All the
crystals of a mineral have
the same basic shape, but
can be different in size.
T
Granite
Quartz crystals
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SCIENCE IN YOUR LIfE
Sedimentary rocks such
as sandstone and limestone
are common building
materials. These rocks can
be cut into blocks which
are used to build strong,
beautiful walls, steps,
fences, and other
structures.
sedimentary
(sed/o men/tor e) rock,
rock that forms from
cemented or pressed
sediments.
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Sedimentary Rocks
Weathering changes igneous and other rocks into
sediments. Many sediments end up on the bottoms of
oceans and lakes. The water and new sediments press
down on old layers of sediments. Those sediments
are pressed and cemented into sedimentary rocks.
This cycle that changes rock into sediment and
sediment into rock can take millions of years.
As the plates forming the earth's crust move, land
that was once at the bottom of an ocean can be slowly
pushed upward. The sedimentary rocks shown below
were formed at the bottom of an ocean and were
slowly forced upward by the movement of the plates.
This shale is a sedimentary rock made of mud and
lay. As new sediments settled to the bottom of a lake
or ocean, they pressed on mud and clay below. The
veight of the new sediments pressed on the mud,
slowly causing the mud to harden into shale.
Notice the sediments in the sandstone. This rock is
made mostly of the mineral quartz. Large grains of
uartz sand were slowly cemented together by tiny
uartz sediments in water. The tiny sediments filled
spaces between the sand grains. How do you think
e quartz sediments formed?
What do you see in the piece of limestone? This
ock is made from dead organisms. As these
rganisms died, their bodies settled to the bottom of
e ocean and were buried by sediments. Bones and
shells became part of the sedimentary rock that
slowly formed from these sediments.
Sedimentary rocks can change back into
- diments. How do you think this change happens?
Shale
Sandstone
Limestone
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metamorphic
(met/a mor /fik) rock, rock
formed when heat and
pressure change the
minerals in igneous or
sedimentary rocks.
.
Layers of metamorphic
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rock
Metamorphic Rocks
Heat and pressure inside the earth can change
igneous and sedimentary rocks into. metamorphic
rocks. How is the cliff below like the hills on page
256? How is it different? The layers in the cliff
below were once granite. As plates of the earth'
crust moved, the granite was pressed and bent. Thi
pressure changed the granite's minerals. The granite
changed into a metamorphic rock called gneiss (nis),
Heat and pressure cause physical and chemical
changes in many kinds of igneous and sedimentary
rocks. Heat and pressure changed limestone into the
marble on page 259. Because of its strength and
beauty, people use marble in buildings. Heat and
pressure changed shale into the slate on page 259.
Slate breaks apart in smooth layers. Slate is often
used for roofs and floors .
Like igneous and sedimentary rocks, metamorphic
rocks can change. Wind, water, and ice can weather
metamorphic rocks into sediments that might later
form sedimentary rocks. Heat inside the earth can
melt metamorphic rocks into magma. What might
this magma then form?
Physical and chemical weathering, erosion, heat,
and pressure constantly change all rocks. The
changes in the rock cycle never stop.
Lesson Review
1. How do igneous rocks form and change?
2. How do sedimentary rocks form and change?
3. How do metamorphic rocks form and change?
4. Challenge! Some mountains are made of all three
kinds of rock-igneous,
sedimentary,
and
metamorphic. How could all three kinds of rock
be found in one mountain?
Study on your own, pages 422-423.
Slate
Marble
When magma cools, minerals in the magma
often form crystals. These crystals have many
shapes, but they can be divided into six main
groups. Find out what the six main groups of
crystals are.
PHYSICAL
SCIENCE
FIND OUT
ON YOUR OWN
259
1. The earth's crust is made of about iWI plates.
2. When the edges of plates bump together and crumple and
fold, a %ft forms:
3. What causes an earthquake?
4. Melted rock from inside the earth that pushes up between
the edges of the earth's plates forms a Ill!: .
5. The moving plates of the earth's crust are mostly made of
LESSON 4
pages 254-259
6. What is magma?
7. When magma cools slowly, my: in the magma often
form large crystals.
8. Magma that reaches the earth's surface is f::l .
9. MJ is a sedimentary rock made of mud and clay
sediments.
10. How is sandstone formed?
11. The bones and shells from dead organisms form part of
the sedimentary rock called %t.
12. Heat and pressure inside the earth can change igneous
and sedimentary rocks intot:W •
13. Heat and pressure can change mil: to marble.
14. Which of the following igneous rocks was formed by
magma cooling very slowly?
A
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