The Earth was formed at the same time as the Sun and the other planets in the solar system. About 4.6 billion years ago, a rotating cloud of dust and gas,called a nebula,contracted under the pull of gravity. The preesure and temperature at the centre of the nebula became so great that it triggered a nuclear reaction. Some of the hydrogen in the cloud fused into helium,releasing great amounts of energy.This was the birth of sun.Farther from the center,material surrounding the sun cooled and collided,building up into larger bodies,which eventually became the planets.The Earth can be divided into three zones according to its density. The outer crust,the mantle and the core in the centre.The layer below the atmosphere are also categorised as the lithosphere,hydrosphere, asthenosphere.
Earth is not compietely round.It is flattened at the ploes and bulges slightly at the equater.Over two-third of the Earth is covered with water.Some amazing facts about the fact:-
Diameter at the poles- 12713 km
Diameter at the equator- 12756 km
Circumference (distance around the earth at the Equator)- 40091 km
Volume- About one thousand billion cu km
Mass- 5.9 thousand billion tonnes
Average density- 5.5 (Water=1)
Surface area- 510 million sq km
Percentage of surface area covered by water- 71 percentage
Age- 4.6 billon years
