THE EARTH - OUR HOME PLANET
The earth stands just in the middle among the nine planets in regard to size. Four planets-Uranus, Neptune, Saturn, and Jupiter are larger than it while four of them Mars; Venus, Mercury and Pluto are smaller than it. The earth is a huge sphere covered with water, rock and soil. Above all, it is surrounded by a coat of air that is called atmosphere. Along with the other eight planets, it also revolves round the sun-the nearest star to it in the galaxy called the Milky Way.
A UNIQUE PLANET
The earth is our home-planet and has various forms of life on it. This life includes human beings, animals, birds, insects and plants. These forms of life are found on the earth because it is at a proper distance from the sun and has livable temperatures in its various parts. No other planet is known to have life on it. So, our earth is a unique planet in this respect.
The earth's crust is made of rock, it is under water or soil. Beneath the crust, the earth is very hot. The earth is constantly spinning like a top from west to east. At the same time, it is revolving around the sun. The two motions are called rotation and revolution respectively.
Rotation of the earth causes days and nights on it while its revolution, coupled with the tilt in its axis, leads to changes in season and difference in the lengths of the day and the night.
Study of the earth is called geology. The atmosphere of the earth contains enough oxygen to support animal life. This gas is highly active and forms about 21 % of the atmosphere. About 78% of it is nitrogen. The remaining 1 % of it has dust, water-vapor and other gases-carbon dioxide, argon etc.
There are three layers of the earth below its crust-mantle, outer core and inner core. The molten metal forms its inner core. It keeps moving and producing electricity inside the earth. This electricity has made the earth a big magnet with a strong force of gravity. The earth is believed to be 4500 million years old. It has only one moon.