Rising
Sea
L evels
Over millions of years, Earth’s sea
levels have risen and fallen. This is
natural. Why does this happen? And
how does it affect Earth’s surface?
During cold climate periods, or
ice ages, the sea level falls. Water
evaporates from the oceans. That
precipitation becomes ice in gigantic
glaciers and huge ice fields. About
20,000 years ago, it was much colder
than it is today. The sea level was about
400 feet (125 meters) lower than it is
now. That’s equal to ten school buses
stacked on end! But, as the climate
warmed, a lot of the ice melted back
into the oceans and the sea levels rose.
Sea levels are highest during warm
climate periods, or inter-glacials. We
are in an inter-glacial now. This period
started about 10,000 years ago.
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Ocean water is also warmer.
And, warm water takes up more
space than cold water. Each drop
of water expands as it gets warmer.
So how does the sea level change
the surface of Earth? The land in
very cold places, like Greenland
and Antarctica is different. Glaciers
and fields of ice are melting. Plants
and animals that need a cold
climate can’t live there anymore.
In places near the ocean, land
is getting flooded more and more.
Beaches are becoming smaller
because the sand is being taken
out to sea. Salt water from the
ocean moves into freshwater rivers
and streams. The plants and animals
there have to move to other places
with fresh water.
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One place that is affected by rising
sea levels are the Maldives, a group of
small islands in the Indian Ocean. It is
one of the smallest countries on Earth.
It’s also the lowest. The highest point
of land is only seven and a half feet
above sea level. If the sea levels keep
rising, the Maldives could disappear
completely!
India
Maldives
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H
ave you ever wondered how
the surface of Earth gets many
of its different shapes? It’s partly
because of erosion.
EROSION
Erosion is the process that breaks
things down. During erosion, small
pieces of rock or soil move from one
place to another. So, you can think
of erosion as a way that bigger things
are broken down into smaller things.
The usual tool of erosion is water.
Think about a rock that you pick up at
the ocean or in a river. It is probably
very smooth. That’s because, over time,
water has worn off all the sharp pieces.
Now think about the mud next to a
river or stream. That’s an example
of erosion. The water is brown because
it has taken away many tiny bits
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of soil. And the shape of the river or
stream is changed, even if only a little.
Water can even break large boulders.
It doesn’t seem like water is strong
enough to break down and carve out
rock, does it? However, moving water
is amazingly powerful.
over again. The rocks break and the
water takes them away. On a sandy
beach, the waves take away the sand
and put it somewhere else.
Wow! Did you ever think that the
same water you drink could change
Earth’s surface?
One famous example of erosion
by water is the Grand Canyon. For
five million years, the rushing water
of the Colorado River broke off
small pieces of rock and carried
them away toward the sea. Today,
the Grand Canyon is one mile
deep and, in some places,
DID YOU
KNOW?
eighteen miles wide. And
it’s all because of erosion!
At the bottom
Erosion also changes
the shape of coastlines.
Waves hit rocks over and
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of the Grand
Canyon are rocks
that are 1.8 billion
years old.
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Glaciers
Water is a powerful force. And in
its solid form, ice, it can change the
shape of mountains and valleys.
A glacier is a river of ice. As a
glacier moves, it erodes the land. How
does it do this? There are two ways.
The first way is called plucking.
Plucking is when the glacier breaks off,
or plucks, large pieces of the ground
and carries them away. These large
pieces leave big holes and long, deep
grooves in the ground.
DID YOU
KNOW?
The second way
Ten percent of
is called abrasion.
land area on
Abrasion is when the
Earth is covered
with glacial ice.
glacier takes away
smaller pieces of rock.
These smaller pieces act like sandpaper
to Earth’s surface. They smooth down
and polish larger rock surfaces.
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Erosion by glaciers happens very
slowly. How slowly? It can take a glacier
hundreds or even thousands of years
to change the surface of Earth.
One example of glacial erosion is in
California’s Yosemite National Park. In
Yosemite, glaciers have carved away
the sides of mountains, making high
rock walls and deep valleys.
Another example of glacial
erosion are the fjords in Norway.
A fjord is a long, narrow inlet
of water that starts inland and
goes out to sea. The glaciers
cut out valleys with high, steep
sides. A fjord can be thousands
of meters deep. The water
of a fjord is very calm, so it
is a good harbor for boats.
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Many fjords have coral reefs at the
bottom. These reefs are the home
of many kinds of fish and plant life.
Skerries are found near fjords. A
skerry is a small rocky island. Skerries
are formed by glaciers, too.
Glaciers take away soil and rocks,
but when they do that, they make
islands, valleys, and even a place
for fish to live!
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Frost
Wedging
Earth’s surface is always changing.
One way that it changes is by frost
wedging. Frost wedging happens
in many places in the world where
the temperature rises above or falls
below the point of freezing (32 degrees
Fahrenheit). So how does frost wedging
happen?
Rocks have cracks that start on
the surface but don’t go all the way
through the rock. These cracks are
called joints. When it rains, water falls
into the cracks in the
rocks. The water can
stay in the joints for
a long time. Then,
when the temperature
goes below freezing,
the water becomes ice.
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Believe it or not, water can change
its volume, or how much space it fills.
When water goes from liquid to solid,
it expands, or gets bigger. So, when
the water in the joint freezes and
becomes ice, it gets bigger. This ice
pushes against the sides of the joint,
just like if you were standing in the
middle of the joint and pushing the
sides apart with your arms. The joint
becomes wider.
Then, when the temperature rises
and the ice melts, it rains again. Now,
the joint is a little wider and more
water can get into it. When the
temperature drops again, the water
freezes, expands, and pushes the
joint open a little more. This process
happens again and again until the
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rock breaks apart and the pieces
tumble down.
You can see where frost wedging
has happened around you. Just look
for places with lots of sharp, broken
up rocks, like at the bottom of a
hillside. Or, large rocks that have
big splits down the middle of them.
DID YOU
KNOW?
It can take a
year for a rock
to crack from
frost wedging.
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2
W
ater is a powerful force of nature.
When there is too much water too fast,
it’s called a flood. A flood can change
Earth’s surface.
Flooding can happen anywhere
with rivers, a coastline, or streams. One
example of flooding is when there are
days of heavy, steady rain. The water
level in the river rises and goes over
its banks. Another way a flood can
happen is when snow melts very
quickly and the water runs into
the rivers. Then the river overflows.
One more example of flooding is when
wind from a storm in the ocean pushes
large amounts of water onto land.
One kind of flooding happens
quickly and without much notice. It’s
called a flash flood. A flash flood
happens when there is a lot of rain
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Connecting Passage
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1
in a short period of time. A river
floods with no warning to the people
who live around it. In a narrow
canyon or valley, floodwater can flow
very quickly. It can be extremely
destructive. It can wash away houses
and trees, farms and buildings. A flash
flood on a mountain can erode the soil
and wash it down the slopes.
Flash floods can also happen
because of an ice jam. In cold
weather, the waters of a river can
turn to ice. If the weather warms
up suddenly,
DID YOU
KNOW?
the ice can
Flooding along the banks of
break into big
the Nile River in Egypt is an
chunks. These
big chunks can
In ancient times, farmers
knew that the higher the
move down
the river and
their crops would be.
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then pile up at a narrow point or turn
in the river. This ice jam stops the
natural flow of the river and the river
overflows its banks.
Any kind of flood can destroy farms
and make them unusable. But floods
can also be helpful. A flood can bring
a large amount of water and sediments
to fields. These sediments give the land
nutrients so crops can grow.
Connecting Passage
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STUDENT RESPONSE SHEET
INDIVIDUAL READING
Name
Key Question
How does water change Earth’s surface?
On Your Own
1. Read the Key Question. Then read the passage. Look for information in
the article that helps you answer the Key Question. Circle or underline
these details.
2. Now look back at the article. Write the details you circled or underlined on
the Main Idea and Details Ladder below.
Main Idea:
3. Think about the Key Question. Write your answer to the Key Question
using the details you found in the article you read.
My First Answer
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STUDENT RESPONSE SHEET
TEAM DISCUSSION
Name
Key Question
How does water change Earth’s surface?
Share Your Ideas
Meet with your team. Talk about each article your team read.
1. Tell the team what you learned in the article you read. Show the Main Idea
and Details Ladder you made.
2. Look at the ladders your team made. Compare the details in each of
your stories by looking at the information in your Main Idea and Details
Ladders. Answer these questions together.
sHow is the main idea in each article similar?
s)NWHATWAYSDOESWATEROFTENCHANGEASURFACE
Next, write the details that answer the Key Question on the Main Idea and
Details Ladder below. Write only the details that are in every article your
team read.
Main Idea:
Answer the Key Question
Review the details on your team’s ladder. As a team, write an answer to the
Key Question. Use the details from the article to support your answer.
How does water change Earth’s surface?
Our Team’s Answer
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