Changes to Earth’s Land

Grade 3 SS3E2 Students will investigate fossils as evidence

of organisms that lived long ago

What is weathering?

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.

How does weathering happen?• 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.

Erosion• 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/ProvidenceCanyonrosion

• 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.

Other cause of erosion

• 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.

Deposition

• 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.

What’s in Soil?• 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.

Types of Soil• 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.

Types of Soil• 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.

Soil Layers• 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 SoilSoil 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

Fossils• 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.

How do fossils form?• 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.

Kinds of Fossils• 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.

Fossils• 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.

Record in the Rocks• 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.

Georgia’s State Fossil• 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.

A imprint of an animal that lived long ago is not likely to

give clues about that animal’sA. ShapeB. ColorC. SizeD. weight