The surface of the earth is a complex zone. It can be divided into three main portions, viz. lithosphere, atmosphere and hydrosphere.
- The solid portion of the earth is called lithosphere.
- It is composed of rocks of the earth’s crust.
- There is a thin layer of soil on top that contains mineral nutrients which sustain various organisms.
- The earth’s surface can be divided into two main parts, viz. the continents and the ocean basins.
(i) Continents: The huge landmasses on the earth are called continents.
(ii) Ocean Basins: The huge water bodies on the earth are called ocean basins.
- There are seven continents and all of them are separated by large water bodies. The seven continents of the world are; Asia, Europe, Africa, North America, South America, Australia and Antarctica.
- Asia: This is the largest continent. Asia covers about one-third of the total land area of the earth. This continent lies in the eastern hemisphere.
- Europe: Europe lies to the west of Asia and is much smaller than Asia. It is bound by water bodies from three sides.
- Africa: Africa is the second largest continent. The major portion of Africa lies in the northern hemisphere.
- North America: It is the third largest continent. North America and South America are connected to each other by the Isthmus of Panama.
- Isthmus: A narrow strip of land which joins two landmasses is called isthmus. North America lies in the northern hemisphere and western hemisphere.
- South America: A major portion of South America is in southern hemisphere. This continent is surrounded by two oceans, viz. the Atlantic and Pacific oceans.
- Australia: This is the smallest continent. It lies entirely in the southern hemisphere. Since Australia is surrounded on all sides by ocean hence it is called the island continent.
- Antarctica: This is a huge continent and is present on the South Polar Region. In fact, the South Pole lies at the centre of this continent.
- All the oceans of the world are connected to each other. Due to this, the level of sea water is same everywhere. Elevation of land is measured from the sea level and the sea level is taken as zero.
- Waves, tides and ocean currents are the three main movements of ocean water. There are five major oceans, viz. Pacific, Atlantic, Indian, Arctic and Southern oceans.
- Pacific Ocean: This is the largest ocean. It is almost circular in shape. The Pacific Ocean is surrounded by Asia, Australia, North America and South America.
- Atlantic Ocean: This is the second largest ocean. It is S-shaped. North America and South America are to the west of this ocean. Europe and Africa are on the east of this ocean.
- Indian Ocean: Indian Ocean is the only ocean to be named after a country. This ocean is almost triangular in shape. Asia is towards north, Africa is towards west and Australia is towards east of this ocean.
- Southern Ocean: This Ocean encircles Antarctica. It extends northwards up to 60oS latitude.
- Arctic Ocean: This Ocean is within the Arctic Circle. It surrounds the North Pole. It is bound by the northern coasts of North America and Eurasia.
- Atmosphere plays an important role in the environment on earth.
- Atmosphere is made of air which is composed of many gases, water vapour and dust particles.
- Composition of Air: Air is mainly composed of nitrogen and oxygen. 78% of the air is composed of nitrogen, 21% is composed of oxygen and rest 1% is composed of carbon dioxide, argon and many other gases.
- Role of Nitrogen: Nitrogen is important for plants because plants make many important molecules from nitrogen.
- Role of Oxygen: Oxygen is required by living beings for respiration. Moreover, oxygen is also required for burning various fuels.
- Role of Carbon Dioxide: Carbon dioxide is utilized by plants during photosynthesis. You may recall that photosynthesis is the process by which plants make food.
Layers of Atmosphere
- The atmosphere can be divided into many layers.
- Troposphere is at the bottom. This is followed by stratosphere, mesosphere, thermosphere and exosphere.
- The density of atmosphere changes with height. Air is at maximum density at the sea level and becomes rarer as we go higher.
- Humans are comfortable while breathing under normal pressure. When the atmospheric pressure becomes low, it becomes difficult to breathe.
- Atmospheric pressure is very low at high mountains. Due to this, mountaineers need to carry oxygen cylinders so that they can breathe comfortably at high altitude. The difference in pressure also plays a role in wind movements.
- Air moves from high pressure to low pressure. Moving air is called wind.
More than 71% of the earth’s surface is covered with water. But 97% of the total water on earth is available as saline water in oceans and seas.
- The narrow zone of contact between the lithosphere, hydrosphere and atmosphere is called biosphere.
- Life exists in this zone. A variety of organisms exist on earth. All the living beings are linked to each other for their survival. They are also linked to various non-living things for their survival.