NCERT Class 8 Science Curiosity Chapter 13 Our Home Earth a Unique Life Sustaining Planet PDF Download

Chapter 13: Our Home: Earth, a Unique Life Sustaining Planet

Probe and ponder

• What do you think Earth would look like if there were no life on it at all?
• Life on Earth has survived for billions of years. What allows it to keep going despite major changes and disasters?
• Why don't dogs lay eggs? Or hens give birth to live chicks?
• If a spaceship carried soil and water to Mars, could plants start growing there?

We have now reached the final chapter of this book, the concluding chapter in our scientific journey through the middle stage. It is time to put together all that we have seen and learnt and try to understand why our home, planet Earth, is like no other place in the known universe. As you have learnt in Curiosity, Grades 6 and 7, the Earth is a planet orbiting the Sun. However, it is not just any planet. It is a planet that sustains life - full of diverse landscapes, from towering mountains and vast oceans to endless deserts and lush forests. Today, our satellites allow us to take amazing pictures of our planet. The image in the beginning page was taken by an Indian Space Research Organisation (ISRO) Earth Observation Satellite and made by combining nearly 3000 smaller images, like pieces of a mosaic. Although it looks beautiful, it's a false colour image, where scientists use different colours to show different types of information. These satellite images help us study plants on land and tiny organisms in the ocean, and can even detect things like ocean temperature, oil spills, and wind direction. In this chapter, we will uncover the unique conditions that make Earth the perfect home for living beings.

13.1 Why Is Earth a Unique Planet?

What makes the Earth so special? While there are perhaps billions of planets in the universe, Earth is the only one where life, as we know today, exists and thrives in all its forms.

Have you ever wondered where all life on Earth actually exists? All the mountains, rivers, forests, animals, and people are found on just a very thin layer on the surface of our planet. From the tallest mountain to the deepest ocean trench, the crust, where all of life exists, is tiny compared to the size of Earth. If Earth were the size of an apple, the crust would be as thin as the apple's skin as shown in Fig. 13.1. This delicate, life supporting layer is what makes Earth truly special.

[Figure 13.1: The Earth's crust is like the thin skin of an apple, See in your textbook]

Teacher's Note

The crust is just the outermost layer where life exists. When you see the apple analogy, remember that beneath the crust are several other layers (the mantle and core) that are much thicker, but life cannot survive in those extreme conditions. The crust's thinness compared to Earth's total size shows how precious and limited the habitable space actually is.

Let us conduct an activity to list out some features of the Earth that you think make it special.

Activity 13.1: Let us find out

• List some features of the Earth that we often take for granted, but are interesting and important to us. Write them in Table 13.1. We have filled in a few for you.

Discuss the features you have listed with your teacher and friends. You may realise that the Earth is interesting and important to us in many ways. It provides us with the air that we breathe, the water that we drink, and the soil that helps in growing crops. The Earth also provides us materials like rock and timber with which we build our homes, buildings, and roads. You must be curious to know what makes the Earth a unique planet which not only allows life like us to exist but also sustains it.

13.2 What Do the Planets of Our Solar System Look Like?

In Curiosity, Grade 6, you had studied the solar system in the chapter 'Beyond Earth'. Let us recall some of the things we had learnt. Our solar system has eight planets that go around the Sun in nearly circular orbits. In order of their increasing distance from the Sun, they are Mercury, Venus, Earth, Mars, Jupiter,

Teacher's Note

When listing or comparing planets, always remember the order from closest to farthest from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Earth is the third planet, not the first. Many students confuse this because Mercury comes first, but Earth is our home and happens to be in the middle of the inner planets.

Key Points

• Earth is the only known planet where life exists in all its diverse forms, making it unique among billions of planets in the universe.
• All life on Earth exists in a very thin layer called the crust, which is proportionally as thin as an apple's skin compared to Earth's entire size.
• The Earth provides essential resources like air, water, soil for crops, and materials such as rock and timber that support human life and civilization.
• Our solar system contains eight planets orbiting the Sun, with Earth being the third planet in order of increasing distance from the Sun.

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