Earth: Evolution and Basics of Earth

The earth broke off about 4.5 billion years ago with an explosion.
It was a burning hot white mass of gas and dust.
Over a long period, dust and gas gradually condensed to form solid rock.
Such condensation and shrinking made the earth heat up so much that the rock melted into a gluey liquid.
After millions of years, the outer surface of the earth or the earth’s crust cooled and formed hard rock again, just as melted wax solidifies upon cooling.
The interior of the earth is still very hot.
The crust of the earth was formed from the cooling and hardening of the molten matter and hot gases.
With the cooling of the earth, the crust hardened and formed the land.
Cooling of the earth also condensed water vapour into liquid water filling the depressions to form seas.

Earth is the only known planet where life exists.
Its surface area is covered with two-thirds of water and so it is called the blue planet.
Earth is the third planet from the sun, the densest planet in the solar system, the largest of the solar system’s four terrestrial planets.
It is slightly flattened at the poles, that is why its shape is described as a Geoid.
Our Earth is around 4.5 billion years old.
Earth revolves around the Sun once every 365.25 days – this is known as one Earth year. But every four years, February has 29 days instead of 28, so there are 366 days in the year. This is called a leap year.
The surface of Earth is covered by water, around 71%. Only 29% of Earth’s surface is covered by land.
The atmosphere of Earth is divided into 6 layers – the troposphere, stratosphere, mesosphere, thermosphere, exosphere, and ionosphere.
Earth has only one satellite – the Moon.