Our Home Earth A Unique Life Sustaining Planet Class 8 Notes Science Chapter 13

Students can rely on these Class 8 Science Notes Chapter 13 Our Home Earth A Unique Life Sustaining Planet Class 8 Notes for complete exam preparation.

Class 8 Science Chapter 13 Our Home Earth A Unique Life Sustaining Planet Notes

Class 8 Science Curiosity Chapter 13 Notes

Class 8 Science Chapter 13 Notes – Our Home Earth A Unique Life Sustaining Planet Notes Class 8

→ Atmosphere The blanket of gases surrounding the Earth. It contains oxygen for breathing and protects us from harmful rays.

→ Biosphere The part of Earth where life exists-including land, water, air and all living organisms.

→ Greenhouse effect It is the natural process where gases like carbon dioxide trap heat from the Sun, keeping Earth warm.

→ Habitable zone The region around a star where conditions are just right for liquid water to exist, i.e. not too hot or cold.

→ Ozone layer A layer in the atmosphere that protects us by blocking harmful ultraviolet (UV) rays from the Sun.

→ Magnetic field An invisible force around Earth created by molten iron in the core. It deflects harmful particles from space.

→ Asexual reproduction A type of reproduction where only one parent is involved and the offspring is almost identical to the parent.

→ Sexual reproduction A type of reproduction that involves two parents. Offspring have features from both and show variety.

→ Zygote The first cell formed when the male and female gametes (reproductive cells) fuse during reproduction.

→ Climate change A long-term change in Earth’s temperature and weather patterns, mainly caused by human activities like burning fuels.

→ Biodiversity The variety of living organisms (plants, animals, microbes) found in a region or on the planet. It helps to maintain balance in nature.

→ Which zone around the Sun allows water to stay in liquid form?

→ What helps Earth hold its atmosphere, its size or its speed?

→ Name the gas in the atmosphere that helps us breathe.

→ What protects us from harmful rays of the Sun , the ozone layer or clouds?

→ What does Earth’s magnetic field protect us from?

→ Is the magnetic field of Earth visible or invisible?

→ Why is oxygen important for animals and humans?

→ How does carbon dioxide help plants?

→ How do decomposers help in nature?

→ What helps nature to work like a system?

→ How does the formation of zygote ensure that the offspring gets traits from both parents?

→ What happens to the ovule after fertilisation in a flower?

→ Why do frogs lay their eggs in water?

→ Name one agreement signed to protect the ozone layer.

→ Explain how climate change is connected to the burning of fossil fuels.

Earth

Earth is the only planet we know where life can survive.
All plants, animals and people live on a very thin outer layer called the crust, which is as thin as an apple’s skin compared to the whole Earth. Below the crust are other layers-the mantle and the core. This thin crust makes Earth a special place for life.

Structure of Earth

Just like a fruit has layers – skin, flesh and seed, Earth is also made up of layers. These layers are the crust, mantle, and core, each with different properties.

Layer	State	Location	Key Features
Crust	Solid	Outermost lyaer	Thin, rocky layer, includes continents and ocean floors
Upper Mantle	Solid/Semi-solid	Beneath the crust	Slowly flowing rock involved in tectonic movement
Lower Mantle	Solid	Below the upper mantle	Hotter, denser rock, show convection currents
Outer Core	Liquid	Surrounds the inner core	Made of molten iron and nickel, generates magnetic field
Inner Core	Solid	Centre of the Earth	Extremely hot, solid iron and nickel due to high pressure

Solar System

When we go beyond the Earth, we enter the solar system, where we find other planets like Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

These planets revolve around the Sun and form a part of our celestial neighbourhood in space.

Venus is the second planet from the Sun. It is also the hottest planet due to thick carbon dioxide atmosphere. It is also called Earth’s “sister planet”

Greenhouse Effect

The greenhouse effect is a natural process that warms the Earth’s surface. It is essential for life, but too much of it leads to global warming.

Sunlight reaches Venus and like on Earth, the surface absorbs it and sends it back as heat (infrared radiation).

But on Venus, the thick layer of COztraps nearly all the heat. This causes an extreme greenhouse effect.

Greenhouse used for growing plants both keep things warm, but they work differently. On Earth or Venus, gases like carbon dioxide trap heat. These gases stop the heat from escaping after the Sun warms the planet. This helps keep the planet warm. But a plant greenhouse is a closed space made of glass. Sunlight goes in and warms the air inside. The warm air gets trapped and cannot go out easily, so the inside stays warm. So, both keep things warm, but in different ways.

Earth Suitable for Life

Position of the Earth

Earth’s position in the solar system is just right not too close, not too far from the Sun.

Habitable Zone
The region around a star where liquid water can exist is called the habitable zone. It is also known as the ‘Goldilocks zone’, meaning it is “just right” for life.

This zone is essential for the development and sustenance of life in all its forms.
Earth is called the Blue planet because most of its surface is covered with water.

Mars lies at the edge of the Sun’s habitable zone. Spacecraft and rovers have explored it, but no signs of life have been found so far. However, scientists believe that long ago, Mars may have had liquid water, even lakes and conditions suitable for simple life.

Size of the Earth

• Right Size for Atmosphere : Earth’s size (mass) creates gravity strong enough to hold onto its atmosphere.
• Consequence of Being Too Small : If Earth were smaller (with the same density), its gravity would be too weak to retain atmosphere (like Mars’s thin air or Mercury’s lack of atmosphere).
• Consequence of Being Too Large : If Earth were much larger, its gravity would be crushingly strong.
• Oxygen for Breathing : Atmospheric oxygen enables respiration for most life forms.
• Ozone Layer Formation : Some atmospheric oxygen forms ozone (O₃).
• Ozone Shield : The ozone layer blocks the Sun’s harmful ultraviolet (UV) radiation, protecting living cells.

Magnetic Field of the Earth

Earth behaves like a giant magnet due to the movement of molten iron in its core. This creates a magnetic field around Earth, similar to a bar magnet. The magnetic field is invisible but powerful and plays a big role in protecting life.

Cosmic rays (from space) and solar wind (from the Sun) are harmful high-energy particles. These particles can

1. Reduce the ozone layer
2. Let in harmful UV rays

The Earth’s magnetic field acts like a protective shield. It deflects or pushes away many harmful particles. This helps preserve the atmosphere and protect life on Earth.

What Allows Life to Be Sustained on Earth?

Earth supports life because it has the right mix of non-living elements like air, water, sunlight, soil and minerals, along with living beings such as plants, animals and microorganisms. All these parts interact and help each other to keep life going.

Air, Water and Sunlight

Air

1. The air around us is called the atmosphere, which is a mixture of gases like oxygen and carbon dioxide.
2. Oxygen is used by humans and animals for respiration.
3. Carbon dioxide is used by plants to make food through photosynthesis.
4. During photosynthesis, plants release oxygen back into the air.
5. This keeps a balance of gases in nature and supports life.

Sunlight

1. Sunlight is the light and energy we receive from the Sun.
2. Plants need sunlight to make their food (photosynthesis).
3. Sunlight provides energy to all living beings.
4. The heat from the Sun is trapped by gases in the air, creating the greenhouse effect.
5. This effect keeps the Earth warm enough for water to stay in liquid form.
6. Without it, Earth would be too cold to support life.

Water (Hydrosphere)

• All the water on Earth’s surface (oceans, lakes, rivers, etc.) is called the hydrosphere.

• Water covers about 70% of Earth’s surface.
• Found in ponds, lakes, rivers, seas, oceans and groundwater.
• In plants helps move nutrients.
• In animals helps in digestion, temperature control and hydration.
• Water vapor forms clouds, brings rain or snow and refills rivers and lakes.
• Rainfall decides which plants and animals can live in a region.
• Water shapes weather, farming and life on land.

Soil, Rocks and Minerals

Geosphere

• The solid outer part of the Earth made of rocks, soil and minerals is called the geosphere.
• Supports both ecosystem and human life.
• Soil helps plants grow and provides nutrients.
• Minerals in soil give us useful things like
  1. Salt, coal, oil
  2. Metals such as iron and copper
• Soil is rich in nitrogen and potassium, needed by plants.
• These nutrients come from
  1. Slow breakdown of rocks
  2. Remains of dead plants and animals

Geodiversity

• The variety of landforms, rocks, soils and the natural processes that shape them is called geodiversity.
• Geodiversity helps create different habitats that support different kinds of life.
• It is not just background scenery- soil, rocks and water help shape the story of life.
• The non-living parts of nature (like soil and rocks) help living things survive by offering suitable living conditions.

Plants, Animals and Microorganisms

• Nature works like a system. Each living thing plays a role and supports the others. All parts of life are connected and depend on each other, helping to keep life going smoothly on Earth.
• The biosphere is the part of Earth that includes all living beings like plants, animals and microorganisms, along with land, air and water where they live and grow.
• Earth is full of life, from big trees and small shrubs to animals, insects and even tiny organisms we cannot see.
• All living things, along with the places they live, together make up the biosphere. The biosphere includes land, water, and air, where life interacts with its surroundings to survive.
• Plants prepare their food through photosynthesis using sunlight, water, and carbon dioxide. Animals depend on plants or other animals for their food and energy.
• Microorganisms act as decomposers. They break down dead plants and animals and return nutrients to the soil.

The Importance of Balance

• Balance in nature means that all parts of the environment such as land, air, water and living things work together to support life on Earth.
• Earth behaves like a team where nature, weather and life are connected and support one another.
• Even small changes in one part of nature can affect the whole system.
• For example, cutting down forests can reduce rainfall, harm the soil, pollute the air and disturb the homes of animals.
• Life on Earth continues because everything stays in balance and supports each other.
• This balance keeps Earth safe and suitable for living things.
• It is important to protect clean air, fresh water, healthy soil and all forms of life.
• Taking care of this balance helps keep Earth healthy for us and future generations.

Reproduction and Continuity of Life

The balance of nature depends not only on air, water, soil and living beings working together, but also on the ability of living beings to continue their life forms.

Life on Earth continues (Though reproduction, which helps plants, animals and even tiny microbes exist generation after generation.

During reproduction, parents pass on information to their young ones that helps them grow and develop. Young ones usually resemble their parents because each cell carries genes or genetic material that guide how an organism grows and functions. These genes decide how different parts like leaves, bones, muscles, or skin are formed in the body.

Reproduction also brings small changes called variations, which sometimes help living beings survive better. For example

1. Camels developed humps to store fat and survive in deserts.
2. Some bacteria became resistant to medicines over time.

Such changes help life adapt to different environments. So, reproduction not only keeps species going but also helps life adjust and continue in changing conditions as well as maintaining the balance of nature over time.
Reproduction allows life to continue and also brings both similarity and variety. This happens because there are two types of reproduction, i.e. asexual and sexual reproduction.

Asexual Reproduction

In asexual reproduction, only one parent is involved and the offspring are almost exact copies of the parent. This happens because the genetic instructions come from just one source.

Many plants reproduce asexually through a process called vegetative propagation. In this method, new plants grow from parts like the stem, root or leaf. For example

• A money plant can grow from a stem cutting.
• Potatoes sprout from their “eyes”.
• Ginger and sugarcane grow from pieces of the stem. These parts, when given proper air, water and sunlight, can develop into full plants.
  Simple organisms also use asexual reproduction
• Bacteria and amoeba split into two identical individuals.
• Algae can grow from cut fragments.
• Hydra forms buds that grow into new individuals.
• Planaria, a flatworm, can regrow an entire body from a small body part. This process is called regeneration.

Asexual reproduction helps living beings multiply quickly and continue life without the need for two parents.

Sexual Reproduction

In sexual reproduction, two parents, i.e. male and female are involved. Each parent produces special reproductive cells called gametes. These gametes carry only half of the genetic information to ensure that the total does not double with each generation.

When a male gamete (like sperm or pollen) fuses with a female gamete (like egg or ovule), a zygote is formed. This zygote receives one set of genetic instructions from each parent, making the offspring genetically unique.

The zygote then divides and develops into a complete organism. Since the gametes carry different combinations of genetic material, each new individual shares some traits with both parents but also shows variation. This variation helps living beings adapt to their environment and is important for the survival and evolution of species.

Sexual Reproduction in Flowers

Flowering plants have special parts that produce male and female gametes. The anther contains pollen grains, which are the male gametes, while the ovule deep inside the flower holds the female gametes.

The sequence of events involved in reproduction in plants is as follows

• The process begins with pollination, where pollen is transferred to another flower, usually by wind, insects or animals.
• After this, the male and female gametes fuse in a process called fertilisation, forming a single cell called a zygote.
• This zygote develops into a seed. The fleshy part of the flower around the ovule develop into fruit.
• When birds or animals eat the fruit, the seeds often get dropped far away from the parent plant. This helps the plant species spread to new places. Once the seed gets enough water, it starts to germinate, using its stored nutrients to grow roots, shoots and the first leaves

Sexual Reproduction in Animals

In animals, sexual reproduction involves the fusion of two gametes, i.e. the sperm (male gamete) and the egg (female gamete). Fertilisation in animals can happen in two main ways

• External fertilisation : In animals like fish and frogs, fertilisation takes place outside the body, usually in water. The male and female release their gametes into the water, where the sperm and eggs meet and fuse. The development of the zygote into an embryo also happens in water.
• Internal fertilisation : In birds, mammals and humans, the sperm is deposited inside the female’s body, where it travels to meet the egg. Fertilisation happens inside the body, but what happens next differs between birds and mammals.

In birds, the fertilised egg is laid by the female. The zygote develops into an embryo and continues its growth inside the egg, getting nutrition from the yolk until it hatches. Whereas, in most mammals, including humans, the zygote develops inside the female’s body.

The mother’s body provides all the necessary food and oxygen to the developing baby until it is born. This internal development helps protect the growing embryo and allows better care and survival chances.

Threats to Life on Earth

Life on Earth depends on a delicate balance of living and non-living components working together. But human actions are disturbing this balance. Even small changes in global temperature, oxygen levels or the ozone layer can threaten life. The major environmental challenges we face today are climate change, biodiversity loss and pollution. These are together known as the triple planetary crisis.

Climate Change
Climate change refers to the long-term changes in Earth’s temperature, rainfall and weather patterns. One major cause of climate change is the burning of fossil fuels like coal and oil, which release greenhouse gases such as carbon dioxide and methane. These gases trap more heat in the atmosphere, leading to global warming.

Normally, trees, plants and ocean plankton absorb carbon dioxide. But when we release excess carbon that was locked underground for millions of years, the Earth cannot absorb it quickly enough.

Even a slight rise in temperature can

1. Melt ice caps and raise sea levels, flooding coastal cities.
2. Cause extreme weather events like droughts, floods and storms.
3. Reduce crop yields and disrupt food and water supply.
4. Harm human health and wildlife habitats.

Biodiversity Loss

Every living organism plays a role in maintaining the balance of nature. When forests, grasslands, wetlands and other habitats are destroyed, many plants and animals lose their homes. This affects the entire food chain. For example, if grasses disappear, herbivores like deer and grasshoppers struggle to survive. Without herbivores, predators like tigers or foxes lose their food too.

Biodiversity is the key to strong, balanced ecosystems. Diverse ecosystems are more resilient and better able to support life. Local communities can also play a big role in using natural resources wisely and protecting biodiversity.

Pollution

Pollution affects the air, water and soil, further harming life on Earth

1. Air pollution from vehicles, factories and burning fuels causes breathing problems, smog, acid rain and damages crops.
2. Water pollution from plastic, industrial waste and sewage harms aquatic life and makes water unsafe for use.
3. Soil pollution from excess fertilisers and poor waste management reduces soil quality and spreads harmful substances through the food chain.

Global Efforts to Protect the Earth

Nations around the world have come together to protect the environment

1. Montreal Protocol (1987) reduced harmful gases like CFCs, helping the ozone layer recover.
2. Earth Summit (1992) began global discussions on climate change and biodiversity.
3. Kyoto Protocol (2005) and Paris Agreement (2015)

committed countries to reduce greenhouse gas emissions. The Paris Agreement aims to limit global warming to below 1.5°C, though much more effort is still needed.

Individual Efforts to Protect Earth

Individuals play a vital role in protecting the planet. Responsible actions at the personal level can significantly reduce pollution, conserve natural resources and maintain the balance among Earth’s interconnected systems-biosphere, atmosphere, hydrosphere and geosphere. Even small imbalances in oxygen levels, temperature, or ozone concentration can endanger life on Earth.

Some effective steps that individuals can take include

• Reusing, repairing and recycling items such as clothes, plastic and paper to reduce waste and limit environmental damage.
• Saving electricity and water by turning off unused appliances, fixing leaking taps and using energy-efficient devices.
• Promoting awareness by learning about environmental issues, discussing them with others and encouraging eco-friendly practices in the community.

Through such collective efforts, individuals can help protect life on Earth and ensure a sustainable future for all living beings.