The earth is the only planet in the solar system that has life. Life on the earth is possible because of the presence of water, air and suitable temperature. The earth is a unique planet because it has all the major domains that support life.
The earth's surface is divided into four major domains: 1. Lithosphere – the solid rocky part of the earth. 2. Hydrosphere – the water part of the earth. 3. Atmosphere – the layer of gases around the earth. 4. Biosphere – the domain of life, where all the living organisms exist.
In this chapter, we will learn about each of these domains in detail, including the continents and oceans, the layers of the atmosphere, and the importance of the biosphere.
The lithosphere is the solid crust or the hard rocky part of the earth. It is the outermost layer of the earth, made up of rocks and soil.
The lithosphere provides us with forests, grasslands and land for agriculture. It is also the source of minerals and fuels. The major landforms of the lithosphere are the continents, mountains, plateaus, plains and valleys. The lithosphere is divided into a number of large landmasses called continents, which are surrounded by large water bodies called oceans.
The continents are the large, solid landmasses of the earth. There are seven continents in the world: 1. Asia – the largest continent. 2. Africa – the second largest continent. 3. North America 4. South America 5. Europe 6. Australia – the smallest continent. 7. Antarctica – the continent that is covered with ice throughout the year.
The Asian continent is connected to Europe, and together they form the largest landmass called Eurasia. India lies in the continent of Asia. The highest mountain in the world, Mount Everest, is in Asia, on the border of Nepal and Tibet.
The hydrosphere is the water part of the earth. Water exists on the earth in three forms: solid (ice), liquid (water) and gas (water vapour).
The earth is called the "blue planet" because more than 71 per cent of its surface is covered with water. The hydrosphere includes oceans, seas, rivers, lakes, glaciers and underground water. The large water bodies that surround the continents are called oceans. The continuous cycling of water between the oceans, the atmosphere and the land is called the water cycle or the hydrological cycle.
There are five oceans in the world: 1. Pacific Ocean – the largest and deepest ocean. 2. Atlantic Ocean – the second largest ocean. 3. Indian Ocean – named after India. 4. Arctic Ocean – the smallest and the coldest ocean. 5. Southern Ocean – around Antarctica.
The Pacific Ocean is the largest ocean, covering about one-third of the earth's surface. The Mariana Trench in the Pacific Ocean is the deepest part of the earth. The oceans are connected with each other and are important for trade, climate and the water cycle.
The atmosphere is the thin layer of gases that surrounds the earth. It protects us from the harmful rays of the sun and contains the air that we breathe.
The atmosphere is mainly made up of nitrogen (78 per cent) and oxygen (21 per cent), along with small amounts of other gases like carbon dioxide, argon and water vapour. The atmosphere extends up to a height of about 320 kilometres above the earth. The temperature in the atmosphere decreases with an increase in height.
The atmosphere is divided into five layers: 1. Troposphere – the lowest layer, in which we live and where weather changes occur. 2. Stratosphere – the layer above the troposphere; it contains the ozone layer, which protects us from the harmful ultraviolet rays of the sun. 3. Mesosphere – the layer in which meteors burn up. 4. Thermosphere – the layer with very high temperatures, where radio waves are reflected. 5. Exosphere – the uppermost layer of the atmosphere.
The ozone layer in the stratosphere is very important because it protects living beings from the harmful ultraviolet rays of the sun.
The biosphere is the narrow zone of contact between the lithosphere, the hydrosphere and the atmosphere, where all living organisms exist.
The biosphere is made up of three main types of organisms: plants (flora), animals (fauna) and micro-organisms. Plants and animals are found on land, in water and in the air. The biosphere supports life on the earth, and it is the largest ecosystem in the world. The biosphere is subdivided into smaller ecosystems, such as forests, grasslands, deserts and oceans.
Each domain of the earth is important, and all of them are connected:
Because all the domains are interconnected, we must protect them. Pollution and the overuse of resources are threatening the balance of the domains, and it is our duty to conserve them for future generations.
The balance of the earth's domains is being disturbed by human activities: - Cutting down forests reduces the green cover of the lithosphere. - Polluting rivers and seas harms the hydrosphere. - Burning fuels and harmful gases damage the atmosphere and the ozone layer. - The extinction of plants and animals upsets the biosphere.
We can help by planting trees, saving water, keeping our surroundings clean, and using resources carefully. By protecting the four domains, we protect life on the earth.
| Continent | Special Feature |
|---|---|
| Asia | Largest continent |
| Africa | Second largest continent |
| North America | Has the Great Lakes |
| South America | Has the Amazon river |
| Europe | Mostly in the Northern Hemisphere |
| Australia | Smallest continent |
| Antarctica | Covered with ice all year |
| Ocean | Special Feature |
|---|---|
| Pacific Ocean | Largest and deepest ocean |
| Atlantic Ocean | Second largest ocean |
| Indian Ocean | Named after India |
| Arctic Ocean | Smallest and coldest ocean |
| Southern Ocean | Surrounds Antarctica |
The earth is a unique planet because it supports life, and its four major domains – the lithosphere, the hydrosphere, the atmosphere and the biosphere – work together to make life possible. The lithosphere provides land, the hydrosphere provides water, the atmosphere provides air, and the biosphere is the zone of life where they all meet.
The seven continents and five oceans form the main features of the earth's surface, while the layers of the atmosphere protect and sustain us. Because all the domains are interconnected, we must take care of them. By protecting our land, water, air and living things, we protect the only home we have – the earth.