Download DELHI PRIVATE SCHOOL, DUBAI GRADE 4 GENERAL SCIENCE

DELHI PRIVATE SCHOOL, DUBAI
GRADE 4
GENERAL SCIENCE NOTES ON
A) SOIL
B) SPHERES OF THE EARTH
C) INTERNAL LAYERS OF THE EARTH
D) MOVEMENTS OF THE EARTH
What is Soil?
Soil covers much of the land on Earth. It is made up of minerals (rock, sand, clay,
silt), air, water, and organic material (matter from dead plants and animals).
What is the importance of soil?
Soil provides a substrate for plants (roots anchor in soil), a source of food for
plants, and a home for many animals (insects, spiders, centipedes, worms,
burrowing animals, bacteria, and many others).
A scientist who studies soil is called a pedologist.
Types of Soil: There are many different types of soils, and each one has unique
characteristics, like color, texture, structure, and mineral content. The depth of the
soil also varies. The kind of soil in an area helps determines what type of plants
can grow.
Soil Formation: Soil is formed slowly as rock (the parent material) erodes into
tiny pieces near the Earth's surface. Organic matter decays and mixes with
inorganic material (rock particles, minerals and water) to form soil.
Soil Horizons (layers): Soil is made up of distinct horizontal layers; these layers
are called horizons. They range from rich, organic upper layers (humus and
topsoil) to underlying rocky layers (subsoil and bedrock).
A Horizon - The top, organic layer of soil, made up mostly of leaf litter and humus
(decomposed organic matter).
The layer called topsoil. Seeds germinate and plant roots grow in this dark-colored
layer. It is made up of humus (decomposed organic matter) mixed with mineral
particles.
B Horizon - Also called the subsoil - this layer is beneath the A Horizon and
above the C Horizon. It contains clay and mineral deposits.
C Horizon - The layer beneath the B Horizon and above the R Horizon. It consists
of slightly broken-up bedrock. Plant roots do not penetrate into this layer; very
little organic material is found in this layer.
R Horizon - The unweathered rock (bedrock) layer that is beneath all the other
layers.
What is weathering?
Weathering is the breaking down of rocks, soil and minerals through contact with
the Earth's atmosphere, organisms and waters.
What is Mechanical weathering?
It is physical weathering without change in the chemical composition of rocks, soil
and minerals.
Which are the examples of Mechanical weathering?
A) Swiftly moving water can lift rocks from the bottom of the streams. When they
fall down they collide and causes the breakdown of rocks
B)Ice wedging- Ice wedging causes many rocks to break. This refers to the
repeated freezing and melting of water within small crevices in the rock surface.
The ice expands and thus causes cracks in the rocks.
c) Plant roots grow in cracks. The growing roots put tremendous pressure causing
the rocks to break apart.
What is chemical weathering?
Weathering of rocks by chemicals is called as chemical weathering.
Which are the agents of chemical weathering?
Water, Oxygen and mixing of water and carbon dioxide to form carbonic acid
Soil Erosion:
What is erosion?
The process that breaks up and carries away the rocks and soils that make up the
Earth’s surface is called erosion.
How does human activity cause soil erosion?
- Removing the vegetative covering of an area through deforestation and fire.
- Overstocking and overgrazing.
- Inappropriate farming techniques such as deep ploughing land 2 or 3 times a
year to produce annual crops.
- Lack of crop rotation.
- Over cultivation and compaction which make the soil loose and hence,
easily eroded.
- Over watering of gardens
What is conservation of soil?
Preventing soil erosion is called as conservation of soil.
Which methods can be used for soil conservation?
*the use of contour ploughing and wind breaks;
* leaving unploughed grass strips between ploughed land;
* making sure that there are always plants growing on the soil, and that the soil is
rich in humus (decaying plant and animal remains). This organic matter is the
"glue" that binds the soil particles together and plays an important part in
preventing erosion;
* avoiding overgrazing and the over-use of crop lands;
-Building embankments along the banks of rivers
Spheres of the Earth
Earth is made up of four distinct yet connected spheres.
Earth is divided, yet connected.
All of the processes on Earth are driven by four 'spheres,' which we describe
individually, but are really all connected.
The names of each of these spheres come from Greek words that describe what
they're made of: 'Geo' for 'ground,' 'hydro' for ‘water,' 'bio' for 'life' and 'atmo' for
'air.'
The Geosphere
Since 'geo' means 'ground,' the geosphere describes all of the rocks, minerals and
ground that are found on and in Earth. This includes all of the mountains on the
surface, as well as all of the liquid rock in the mantle below us and the minerals
and metals of the outer and inner cores. The continents, the ocean floor, all of the
rocks on the surface, and all of the sand in the deserts are all considered part of the
geosphere. Basically, if it looks like solid ground, it's part of the 'ground' sphere.
The Hydrosphere
Knowing that 'hydro' means 'water,' you may have guessed that the hydrosphere is
made up of all the water on Earth. This includes all of the rivers, lakes, streams,
oceans, groundwater, polar ice caps, glaciers and moisture in the air (like rain and
snow). The hydrosphere is found on the surface of Earth, but also extends down
several miles below, as well as several miles up into the atmosphere.
Most of Earth's water is salty and in the oceans - about 97%. Two-thirds of the
remaining 3% is frozen in glaciers and polar ice caps. Only 1% of the hydrosphere
is liquid freshwater, and even most of this exists as groundwater down in the soil.
The Biosphere
With the prefix 'life,' this means that Earth's biosphere is composed of all of the
living organisms on the planet. This includes all of the plants, animals, bacteria,
fungi and single-celled organisms found on Earth. Most of this life exists no deeper
than about 10 feet into the ground or about 600 feet above it.
The Atmosphere
The atmosphere, which is the air that surrounds the Earth. This 'air' sphere is made
up of mostly nitrogen, some oxygen and small amounts of many other molecules.
Most of the atmosphere is densely packed near the surface (which is where all of
our weather occurs), but it extends to over 300 miles above ground. However,
exactly where it ends and space begins is difficult to say! The atmosphere acts like
a giant blanket, protecting us from harmful UV radiation and keeping our planet
warm.
Examples of Interaction of Spheres of the Earth
Glen Canyon Dam holds back the waters of the Colorado River to form Lake
Powell.
Several examples of sphere interactions can be inferred from this photograph:
•Humans (biosphere) built a dam out of rock materials (geosphere).
•Water in the lake (hydrosphere) seeps into the cliff walls behind the dam,
becoming groundwater (geosphere), or evaporating into the air (atmosphere).
•Humans (biosphere) harness energy from the water (hydrosphere) by having it
spin turbines (geosphere) to produce electricity
Plants (biosphere) draws water (hydrosphere) and nutrients from the soil
(geosphere) and release water vapor into the atmosphere. Humans (biosphere) use
farm machinery (manufactured from geosphere materials) to plow the fields, and
the atmosphere brings precipitation (hydrosphere) to water the plants.
Energy from the sun is stored by plants (biosphere). When humans or animals
(biosphere) eat the plants, they acquire the energy originally captured by the plants.
Humans expend some of this energy arranging bricks and wood (geosphere and
biosphere) into buildings.
Layers of Earth:
The Earth is made of many different and distinct layers. The deeper layers are
composed of heavier materials; they are hotter, denser and under much greater
pressure than the outer layers.
Core: The Earth has an iron-nickel core that is about 2,100 miles in radius. The
inner core may have a temperature up to about 13,000°F (7,200°C = 7,500 K),
which is hotter than the surface of the Sun. The inner core (which has a radius of
about 750 miles (1,228 km) is solid. The outer core is in a liquid state and is about
1,400 miles (2,260 km) thick.
Mantle: Under the crust is the rocky mantle, which is composed of silicon,
oxygen, magnesium, iron, aluminum, and calcium. The upper mantle is rigid and is
part of the lithosphere
Surface and crust: The Earth's surface is composed mostly of water, basalt and
granite. Oceans cover about 70% of Earth's surface. These oceans are up to 3.7 km
deep. The Earth's thin, rocky crust is composed of silicon, aluminum, calcium,
sodium and potassium.
Movements of Earth
1.Rotation- the spinning movement of the Earth on its axis is called rotation. An axis is
an imaginary line running from the North Pole to the South Pole of the Earth. It is tilted
at an angle of 23.5 degrees. Rotation causes day and night. The Earth takes 24 hours to
rotate once.
2.Revolution – the movement of the Earth around the Sun in its orbit is called
Revolution. Revolution causes seasons. The
Earth takes 365 and a quarter days to
complete on revolution. The tilt of the Earth’s
axis and revolution causes seasons.
Concept Learning Notebook
Task 1: Observe the given diagram and answer the questions that follow:
Process Success Criteria:
1. Make a table and write the season in the Northern and Southern Hemisphere for
each of the given position A, B, C and D.
2. Predict what would happen if the Earth’s axis was not tilted.
Position A
Position B
Position C
Position D
Northern
Hemisphere
Summer
Autumn
Winter
Spring
Southern
Hemisphere
Winter
Spring
Summer
Autumn
If the Earth’s axis was not tilted then there would have been no seasons.
Task 2: Study the given diagram and answer the questions that follow:
Process Success Criteria:
1. Identify what the above picture is showing.
2. List the stages in the formation of soil.
3. Which part of the soil is most fertile? Why?
1. Formation of soil
2. The stages in the formation of soil are:
a. Bedrock begins to disintegrates ( break)
b. Organic material facilitates disintegration
c. Horizons form
d .Developed soil supports vegetation
3. The most fertile part of the soil is A Horizon or top soil as it has humus or
organic matter.
Extra Questions ( Not to be written in the CL note book)
1. Describe the spheres of the Earth.
The Geosphere
Since 'geo' means 'ground,' the geosphere describes all of the rocks, minerals and
ground that are found on and in Earth. This includes all of the mountains on the
surface, as well as all of the liquid rock in the mantle below us and the minerals
and metals of the outer and inner cores.
The Hydrosphere
The hydrosphere is made up of all the water on Earth. This includes all of the
rivers, lakes, streams, oceans, groundwater, polar ice caps, glaciers and moisture in
the air (like rain and snow). The hydrosphere is found on the surface of Earth, but
also extends down several miles below, as well as several miles up into the
atmosphere.
The Biosphere
Earth's biosphere is composed of all of the living organisms on the planet. This
includes all of the plants, animals, bacteria, fungi and single-celled organisms
found on Earth.
The Atmosphere
The atmosphere, which is the air that surrounds the Earth. This 'air' sphere is made
up of mostly nitrogen, some oxygen and small amounts of many other molecules.
3. Describe the formation of a volcano.
Ans: The molten rock present in the mantle known as magma gushes out with a
great force from weak places in the crust forming a cone shaped mountain known
as a volcano.
4. What is an orbit?
Ans: The elliptical path along which the Earth moves around the Sun is called its
orbit. The orbit is an imaginary path along which the heavenly bodies move.
6. List the different layers of the Earth.
Ans: The different layers of the Earth are Crust, Mantle and Core.
7. How are seasons caused?
Ans: Seasons are caused due to the tilt of the Earth’s axis and its revolution around
the Sun.
8. How long does the Earth take to go around the Sun once?
Ans:The Earth takes 365 days or one year to go around the Sun once.
9. Define rotation, revolution and Solar year.
Ans: The spinning movement of the Earth on its axis is called rotation. It causes
day and night .It takes 24 hours to complete one rotation.
The Earth moves around the Sun on its orbit. This movement of the Earth is called
the revolution of the Earth. It takes 365 days to complete one revolution. It causes
seasons. The time taken by a planet to complete one revolution around the Sun is
equal to a solar year of that planet.