Objective of the chapter: Our Earth - Class 4
You will learn about:
- the solar system and the heavenly bodies
- why Earth is a special planet
- air, water and soil present on Earth
Earth is a special planet in our solar system. It is the only planet known to have life.
The earth has air, water and soil. These are needed by the plants and animals that live on the earth. Air, water and soil are not found together in any other planets of the solar system.
The Solar System
The sun, eight planets and their moons, together with smaller bodies in the form of asteroids, meteoroids, and comets form the solar system.
The planets and their moons, asteroids, meteoroids, and comets are called heavenly bodies.
The sun is a star. It holds all the heavenly bodies together and gives them heat and light.
Asteroids: Asteroids are large, rocky objects found between the planets Mars and Jupiter. They are much smaller than the planets.
Meteoroids: A meteoroid is a small rocky or metallic body in outer space. They are much smaller than asteroids. When a meteoroid enters the earth's atmosphere, it burns and appears as a streak of light. We then call it a shooting star or meteor.
Comets: Comets are small icy objects that goes around the sun. When they come near the sun, they glow and get long, bright tails of gas and dust.
How planets were formed?
The solar system was very different millions of years ago. It was a very hot place that had only gas and dust. Over time it cooled and rocks & ice were formed.
The rocks joined to make the rocky planets like the earth, while the ice formed the icy planets like Neptune.
In the beginning, the earth was very hot. Slowly it cooled down and a layer of air formed around it. Clouds in the air brought rain, which formed oceans and lakes. Now the earth had air, water and soil. It received sunlight, which plants need to make food. Gradually, living beings appeared and developed to what they are today.
The Earth - A Living Planet
Earth is the only planet to have life. You may be thinking why only the earth has life and not on other planets of the solar system.
There is life on the earth because:
- It has water in the liquid form.
- It has air needed by plants and animals to live. The air has life-supporting gases like oxygen.
- It is at the right distance from the sun, which makes it neither too hot nor too cold. Had it been as close to the sun as Mercury, it would have been very hot. So hot that its water would have turned into steam. Had it been as far away as Neptune, its water would have have frozen to ice.
Now you know the reasons why the earth is called a unique planet.
The earth is surrounded by a layer of air called the atmosphere. Air is a mixture of gases like oxygen, carbon dioxide and water vapour.
Oxygen is needed by plants and animals to breathe. Carbon dioxide is used by plants to make food. And water vapour is needed for rain clouds to form.
The atmosphere makes the earth livable in many other ways. It acts as a blanket that traps heat. This does not let the earth become too cold at night. It acts as a shield too.
For example, it makes most meteoroids burn up before they hit the ground.
Water is found on the earth in three forms - solid, liquid and gas.
As a solid, it is found as ice near the poles. As a gas, it is found as water vapour in air. And it is found in the liquid form in rivers, lakes and oceans.
Water is also found in the underground in liquid form.
Liquid water and ice cover about three-fourth of the earth's surface.
Water is very important for life. All living beings are made up of cells, which have water. More than half our body weight is due to water.
Our body depends on water to survive. Every cell, tissue, and organ in our body needs water to work properly.
For example, to maintain temperature, remove waste, and lubricate bone joints, our body needs water. It is needed for overall good health.
We also need water for drinking, cooking, washing and growing crops. Plants need water to make food.
The land on the earth has a thin layer of soil at the top. Most plants grow on soil. Soil has finely broken rocks, the remains of dead plants and animals, air, water and many small organisms.
The dead plants and animals and many of the organisms in the soil make it fertile.
There are pockets (empty spaces) in the soil that hold air and water. Plant roots get air and water from these.
Soil is important for us. Most of our food is grown on soil.
For Class 4
A. Answer these questions.
- Define Solar System?
- What are asteroids?
- What are shooting stars?
- How does atmosphere protect us?
- Why earth is called a special planet?
- Why water is important for us?
B. Write true or false.
- There are 9 planets in our solar system.
- The sun is a star.
- The atmosphere act as a blanket and protects earth from becoming very cold at night.
- Water is found in two forms – solid and liquid.
- Air is a mixture of gases like oxygen, carbon dioxide and water vapour.
- Apart from earth there are life on other planets also.
- Large rocky object found between Mars and Jupiter are called comets.
- Earth is at the right distance from sun, which makes it neither too hot nor too cold.
- Large part of our earth is covered by water.
- Earth is the main source of energy for life.
C. Fill in the blanks.
- The early earth got its oceans after it got its ___________.
- Icy objects that glow as they come near the sun are called ___________.
- Pockets in the soil hold __________ and ___________.
- Millions of years ago, the solar system had just ___________ and dust.
- Water vapour in the atmosphere forms __________.
- More than half our body weight is due to __________.
- There are pockets (empty spaces) in the _______ that hold air and water.
- Water is found as _______ near poles.
- As we climb higher the amount of oxygen in the air _________.
- Air has ________ which is needed to form clouds.
D. Match the following.
|1. High Mountains||a. Star|
|2. Shooting star||b. Meteor|
|3. Large rocky objects||c. Layer of air|
|4. Broken rocks and other things||d. Small organism|
|5. Soil has||e. A living thing|
|6. Sun||f. Soil|
|7. Jupiter||g. Neptune|
|8. Atmosphere||h. Less oxygen|
|9. Icy planet||i. No life|
|10. Organism||j. Asteroids|