Formation of the earth
When you stir flour into hot water, a swirling mass forms. In the same way, long ago a huge spinning cloud in space formed, and from it the sun and planets were made.
About 4.5 billion years ago, a huge spinning cloud of very hot gases and dust in space divided into portions. These formed the sun and the planets.
Rule 1: How the sun and planets formed — An enormous cloud of very hot gases and dust was spinning at great speed. Its circular motion divided it into portions, which made the sun and the planets, including the earth.
In the figure : In the figure this happened about 4.5 billion years ago.
- Easy : Easy: The sun and the planets came from a cloud.
- Medium : Medium: The cloud was made of gases and dust.
- Exam-type : Exam: Its fast circular motion divided it into portions.
Rule 2: Reading big numbers — 4.5 billion = 4,500,000,000, which is 450 crore years. A crore is 10 million, so 450 crore = 4500 million.
- Easy : Easy: 1 billion = 100 crore.
- Medium : Medium: 4.5 billion = 450 crore.
- Exam-type : Exam: 2 billion years = 200 crore years.
Cloud of gas and dust, 4.5 billion years ago, made the sun and planets.
Thinking the earth was always here. It formed about 4.5 billion years ago.
Memory clue: "ढग फिरला, सूर्य-ग्रह बनले".
Spot the difference
| Item | Detail |
|---|---|
| Beginning | Hot cloud of gas and dust |
| Time | About 4.5 billion years ago |
| Result | Sun and planets |
Practice questions
- 1How old is the solar system?
- 2What was the cloud made of?
- 3What did the cloud's circular motion do?
- 4What did the portions become?
- 5Write 4.5 billion in crore.
- 6How many crore make 1 billion?
- 7Why do we say the earth is a part of the solar system?
- 8Why does a spinning cloud break into portions?
Show answers (try them yourself first)
- 1About 4.5 billion years.
- 2Very hot gases and dust.
- 3It divided the cloud into portions.
- 4The sun and the planets.
- 5450 crore.
- 6100 crore.
- 7It formed from the same cloud as the sun and the other planets.
- 8The fast circular motion pulls and throws parts apart, which then gather separately.
Planets of the solar system
If you list the eight planets on the blackboard, the earth sits in the third seat from the sun. Only this seat has green trees and blue water.
The earth is the only planet known to have life. The planets in order are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Rule 1: Planets in order — The eight planets in order from the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Only the earth is known to have life.
In the figure : In the figure the eight planets in order from the Sun; only the earth is known to have life.
Planets of the solar system
In the app you can move this figure with your finger.
Open in the app- Easy : Easy: Earth is the third planet.
- Medium : Medium: Mars comes after Earth.
- Exam-type : Exam: Only Earth is known to have life.
Rule 2: Mars — Mars has ice at its poles but no liquid water. India's Mangalyaan reached the orbit of Mars on 24 September 2014. Before it, ISRO had launched it from Sriharikota in November 2013.
- Easy : Easy: Mars has ice at the poles.
- Medium : Medium: It has no liquid water.
- Exam-type : Exam: Mangalyaan reached Mars on 24 September 2014.
Earth: third planet, only one with life. Mars: ice but no liquid water.
Saying Mars has water like the earth. It has ice at the poles but no liquid water.
Memory clue: "My Very Educated Mother Just Served Us Noodles".
Spot the difference
| Planet | Position from the sun |
|---|---|
| Mercury | 1 |
| Earth | 3 |
| Mars | 4 |
| Neptune | 8 |
Practice questions
- 1Which is the only planet known to have life?
- 2How many planets are there in all?
- 3Which planet comes after the earth?
- 4Which planet is the eighth from the sun?
- 5What is found at the poles of Mars?
- 6Which Indian mission reached Mars and when?
- 7How many planets lie between the earth and the sun?
- 8Why is the earth so special in the solar system?
Show answers (try them yourself first)
- 1The earth.
- 2Eight.
- 3Mars.
- 4Neptune.
- 5Ice.
- 6Mangalyaan, on 24 September 2014.
- 7Two: Mercury and Venus.
- 8It is the only planet known to have life.
Beginning of life
A hot cup of tea cools after some time. The newly formed earth was also very hot, and it took a long time to cool down before water could stay on it.
After the earth formed, about 80 crore years passed before its surface cooled and water bodies formed. Life first appeared in water.
Rule 1: Cooling and water — The earth's surface slowly cooled, and water bodies formed over about 80 crore years. Life first appeared in water.
In the figure : In the figure life first appeared in water.
- Easy : Easy: Life began in water.
- Medium : Medium: The earth first had to cool.
- Exam-type : Exam: Cooling took about 80 crore years.
Rule 2: Time sums — 80 crore years = 800 million years = 0.8 billion years. If the earth formed 4.5 billion years ago, the first water bodies came after about 0.8 billion years. So there were about 4.5 − 0.8 = 3.7 billion years from then till today.
- Easy : Easy: 80 crore = 0.8 billion.
- Medium : Medium: 4.5 − 0.8 = 3.7 billion years.
- Exam-type : Exam: Water bodies formed long before humans appeared.
Earth cooled for about 80 crore years, then water bodies; life began in water.
Thinking life appeared the moment the earth formed. It took a long time.
Memory clue: "आधी थंड, मग पाणी, मग जीवन".
Spot the difference
| Stage | Detail |
|---|---|
| Hot earth | Surface cooling |
| About 80 crore years | Water bodies form |
| After that | Life appears in water |
Practice questions
- 1How long did the earth take to cool and form water bodies?
- 2Where did life first appear?
- 3Was the early earth cool or hot?
- 4Write 80 crore years in billions.
- 5Earth formed 4.5 billion years ago. How long ago did the first water bodies form, roughly?
- 6Why did life not begin straight away?
- 7Why is water necessary for life?
- 8Arrange: life appears, earth cools, water forms.
Show answers (try them yourself first)
- 1About 80 crore years.
- 2In water.
- 3Hot.
- 40.8 billion.
- 5About 4.5 − 0.8 = 3.7 billion years ago.
- 6The earth was too hot and had no water bodies yet.
- 7All living things need water to live, and the first life began in it.
- 8Earth cools, water forms, life appears.
Protozoa and unicellular organisms
A drop of pond water looks clear, yet under a microscope it is full of tiny moving creatures. Our earliest ancestors looked like these.
The first living things were unicellular (एकपेशीय) organisms called protozoa (प्रोटोझोआ), seen only with a microscope.
Rule 1: From one cell to many — The first living things were unicellular protozoa. Multicellular organisms developed slowly from them.
In the figure : In the figure many-celled organisms developed slowly from the first one-celled ones.
- Easy : Easy: Protozoa have one cell.
- Medium : Medium: We need a microscope to see them.
- Exam-type : Exam: Multicellular life came from unicellular life.
Rule 2: Unicellular and multicellular — A unicellular organism is made of one cell, such as a protozoan. A multicellular organism is made of many cells, such as a plant, a fish or a human. Your body has crores and crores of cells.
- Easy : Easy: A protozoan is unicellular.
- Medium : Medium: A human is multicellular.
- Exam-type : Exam: A plant, a fish and a human are all multicellular.
First life = unicellular protozoa. Many-celled life came later.
Thinking protozoa can be seen with the naked eye. We need a microscope.
Memory clue: "एक पेशी → अनेक पेशी".
Spot the difference
| Type | Cells | Example |
|---|---|---|
| Unicellular | One | Protozoa |
| Multicellular | Many | Plant, fish, human |
Practice questions
- 1What were the first living things?
- 2How can we see protozoa?
- 3What does unicellular mean?
- 4What does multicellular mean?
- 5Give two examples of multicellular organisms.
- 6Which came first, unicellular or multicellular life?
- 7Why can we not see protozoa without a microscope?
- 8How did the variety of life increase over time?
Show answers (try them yourself first)
- 1Unicellular organisms called protozoa.
- 2With a microscope.
- 3Made of one cell.
- 4Made of many cells.
- 5A plant and a human.
- 6Unicellular.
- 7They are extremely tiny.
- 8Many-celled organisms slowly developed from one-celled ones and became more varied.
The animal world
A fish swims and breathes through gills, a hen lays eggs, and a cow gives birth to a calf. All of them are animals, and all follow a few common rules.
Every animal breathes, moves for food or other purposes, and either lays eggs or gives birth to young ones.
Rule 1: Common features of animals — All animals breathe, move, and either lay eggs or give birth to their young. A hen and a snake lay eggs; a cow and a dog give birth to young ones.
In the figure : In the figure all animals breathe, move, and either lay eggs or give birth.
- Easy : Easy: A hen lays eggs.
- Medium : Medium: A cow gives birth to a calf.
- Exam-type : Exam: All animals breathe and move.
Rule 2: Sorting animals — Egg-laying: hen, snake, fish, frog. Giving birth: cow, dog, human. Some animals move on land, some in water and some in the air. They all move to find food, to escape danger or to find shelter.
- Easy : Easy: A dog gives birth to puppies.
- Medium : Medium: A frog lays eggs.
- Exam-type : Exam: Animals move to find food or escape danger.
Animals breathe, move, and lay eggs or give birth.
Thinking all animals give birth. Many lay eggs.
Memory clue: "श्वास, हालचाल, अंडे किंवा पिल्लू".
Spot the difference
| Animal | Lays eggs or gives birth? |
|---|---|
| Hen | Lays eggs |
| Snake | Lays eggs |
| Cow | Gives birth |
| Dog | Gives birth |
Practice questions
- 1Name three things all animals do.
- 2Name two animals that lay eggs.
- 3Name two animals that give birth.
- 4Why do animals move?
- 5Where can animals move?
- 6Does a frog lay eggs or give birth?
- 7Sort: fish, human, hen, cow.
- 8How is an animal different from a stone?
Show answers (try them yourself first)
- 1Breathe, move and have young ones (by eggs or birth).
- 2Hen and snake.
- 3Cow and dog.
- 4To find food, escape danger or find shelter.
- 5On land, in water and in the air.
- 6Lays eggs.
- 7Lay eggs: fish and hen. Give birth: human and cow.
- 8An animal breathes, moves on its own and has young ones; a stone does none of these.
Quick revision
- Cloud of gas and dust (4.5 billion years) → sun and planets → water bodies → protozoa → multicellular life.