About 71% of earth is covered with water and 29% is the land mass.
There are 7 continents—
1. Asia (largest), 2. Africa, 3. North America, 4. South America, 5. Antarctica,
6. Europe, 7. Australia (Smallest)
Oceans
There are four oceans. In order of decreasing size, they are:
1. Pacific Ocean, 2. Atlantic Ocean, 3. Indian Ocean, 4. Arctic Ocean.
The waters surrounding Antarctic are sometimes called as the Southern Ocean.
1. Pacific Ocean
The explorer Ferdinand Magellan, who circumnavigated the Earth, named the ocean ‘Pacific’ meaing calm or peaceful.
(i) It is the largest ocean.
(ii) It is the deepest ocean with an average depth of 4,200 m. The Mariana Trench is the deepest trench in the world with a depth of 11,000 m.
(iii) Most of the islands of this ocean are the volcanic or coral origin.
2. Atlantic Ocean
It is the second largest ocean.
(i) The Atlantic Ocean has the longest coastline. This is due to its highly indented coastline.
(ii) The Atlantic Ocean is the busiest ocean for trade and commerce.
(iii) The Atlantic Ocean was formed millions of years ago when a rift opened up in the Gondwanaland and the continents of South America and Africa separated.
(iv) The continental islands of Newfoundland and British Isles are the major ones.
Volcanic islands are fewer and they include those of Cuba, Jamaica and Puerto Rico. Iceland is the largest island of volcanic origin.
3. Indian Ocean
The Indian Ocean is the only ocean named after a country i.e. named after India.
(i) The Indian Ocean is deeper than the Atlantic Ocean.
(ii) It contains numerous continental islands, Madagascar and Sri Lanka being the largest ones.
Islands of volcanic origin are those of Mauritius, Andaman and Nicobar, Seychelles, Maldives and Lakshdweep are of coral origin.
4. Arctic Ocean
It is the smallest of all the oceans. It lies within the Arctic Circle, hence the name Arctic Ocean.
(i) The North Pole lies in the middle of the Arctic Ocean.
(ii) Most of the Arctic Ocean remains frozen with thick ice for most of the year.
(iii) It is the shallowest of all oceans and has an average depth of 1,500 m.
(iv) It has the least salinity of all the oceans. It has a salinity of 20 per thousand.
Biosphere
The portion of the Earth where life exists is called the biosphere.
The Earth is the only planet of the solar system where life exists. Life is possible because earth has lithosphere, a hydrosphere and atmosphere i.e. it has land, water and air.
(i) Lithosphere : The uppermost layer of the Earth’s crust where life is supported called soil.
The soil provides the nutrients for all land organisms, directly or indirectly.
(ii) Hydrosphere : Water available in the gaseous, liquid and solid state, is necessary for the living organisms.
Water also dissolves and transports nutrients from the soil to the plants. It is used by plants for making food. Plants are eaten by animals.
(iii) Atmosphere : It provides an even temperature of the Earth. It protects organisms from the harmful ultraviolet radiations of the Sun.
The different gases in the atmosphere support life. Oxygen helps in respiration to all living beings Carbon dioxide helps in food manufacture by green plants and nitrogen helps in growth.
