Transcript Changes to Earth*s Land

Grade 3
SS3E2 Students will investigate fossils as
evidence of organisms that lived long ago
Weathering is the slow breaking
apart or wearing away of rock into
smaller pieces.
Moving water, wind, ice and
growing plants roots can all cause
weathering.
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In Georgia, most weathering is caused by moving
water. Rocks rub against each other and become
worn down. The rocks become smoother and
smaller.
Wind causes weathering when it picks up rock
particles and blows them against larger rocks. This
wears the rocks away.
Changes in weather can also cause weathering. If
water seeps into cracks of rocks and freezes , the
cracks can get bigger.
Plants are another cause of weathering. Plants can
grow into the cracks, which causes the cracks to
widen. Growing roots can break apart even large
rocks.
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Once a rock is broken down by weathering, the
smaller pieces can be moved by water, winder or
ice in an process called erosion.
Erosion is the movement of weathered rock from
one location to another.
Georgia’s Providence Canyon was formed by
Erosion
http://www.gastateparks.org/ProvidenceCanyonro
sion
Ocean wave erosion can change shorelines. Waves
can wash away sand and rock.
Erosion can cause caves to form.
Ellison’s Cave is an example.
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Wind is another cause of erosion. It can make loose
bits of sand and soil roll and bounce across the
land.
Wind can cause particles and soil to rub against
rocks. New rock shapes are carved by wind over
time.
Gravity causes erosion. This force pulls soil and
rocks downhill. Gravity also moves glaciers. A
glacier is a large mass of slow moving ice that
flows down a slope. As a glacier moves, it collects
rocks and soil. A glacier can carves out
mountainsides to make valleys and canyons.
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Erosion by water, wind, or ice moves particles of sand,
soil and bits of rock called sediment.
Over time, this sediment is dropped to a new place.
The dropping of sediment by wind, water, ice or
gravity is called deposition.
Deposition along the shore causes beaches to form.
This happens when ocean waves crash into land,
depositing sand, rocks and shells.
Rivers carry sediment downhill towards lakes and
oceans. As the land flattens, sediment is dropped. If
this process occurs at the mouth of the river, a large
mass of deposited sediment, a delta is formed.
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Most plants need soil in order to grow. Soil is loose
material that covers most of the Earth’s surface. Soil
is made up of bits of rock, minerals, and material
that was once living.
Soil is formed when rocks are weathered. After
thousands of years, weather rocks mix with humus
to become soil.
Humus is the decayed remains of plants and
animals.
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Sandy soil – particles are medium sized and very
hard.
Silt soil is soft, smooth soil that contains slightly
larger particles than clay
Clay soil is made up of very small, tightly-packed
particles.
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The particle size in the soil affects the way water
drains through soil.
Water passes through the large particles that
make up sandy soil. It passes less easily through
smaller particles that make up silt soil.
When clay particles get wet, they stick together.
Water drains very slowly through clay soil.
Many plants grown well in loam.
Loam is a mixture of sand, silt, clay and humus.
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When wind, moving water, and moving ice slow
down, they drop the sediment they are carrying.
Over time, soil particles and larger pieces of rock
build up and form layers of soil.
There are three main layers.
The uppermost layer is topsoil. Plants grow best
in topsoil since it contains humus.
The layer below topsoil is called subsoil. Subsoil
contains little humus.
Bedrock is the solid rock that lies below subsoil.
Types of Soil
Soil is made up of bits of rock, minerals, and material
from once living things. Soils are classified by the type
of rock bits they contain. Clay soil has tiny particles
packed tightly together. Topsoil and subsoil are soil
layers that lie above bedrock
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Fossils, the remains of once-living things, give clues
about living things long ago.
Scientists know what the Earth is like long ago by
studying rocks and fossils found in these rocks.
A fossil is the preserved remains of a plant or animal
that lived long ago.
Fossils include bones, teeth, shells, and imprints of
organisms that were pressed in mud and sand.
A scientist who studies fossils and organisms is
called a paleontologist.
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Some fossils from when plants and animals die
and are buried in the soil.
Some fossils form when organisms die and leave
imprints in wet soil. Other imprints come from
the footprints of organisms.
Fossils are only part of once-living thing. That’s
why studying one fossil does not always tell
everything about an organism.
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Fossils can form in many ways. Imprints, molds
and casts are three kinds of fossils.
Fossils can be organisms or their parts preserved
in different materials. Amber, hardened mud,
rock, tar, and ice are materials in which fossils
have been found.
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Some fossils are called “petrified”
fossils. A common example is
petrified wood. This happens when
a fossil forms on a tree once it has
died.
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Earth’s surface has changed over millions of
years.
Fossils can give clues about some changes
that have taken place.
Fossils of plants and animals that lived in
warm regions have been found in places that
are now very cold. This shows that the
weather in some places on Earth has changed
over time.
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Georgia’s state fossil is the shark’s tooth.
Summary
A fossil is the preserved remains of a plant
or animal that lived long ago.
Fossils include imprints, molds, casts, and
preserved remains in amber.
Fossils can give us clues about what Earth’s
surface was once like and how it has
changed.
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Shape
Color
Size
weight