There are many theories about how the earth was born. But the most accepted theory is that the earth was born at the same time as solar system, around 4,560 million years ago.

The solar system was formed by a cloud of gas and dust which called a nebula.

Inside a nebula, all the elements known to man were formed in the centre by gravity, this was the start of the formation of the sun, and at this stage it was called a protostar. The heat from this process flattened the nebula into a spinning disk shape with a bulge at the centre. Later there was a big explosion, and the sun was born in the centre of that explosion. This explosion or nuclear fusion reaction released massive energy. Gas and dust that orbited around the sun formed planets. The rest of the gas and dust which were too far away from the sun remained is far off space as ice and dust and eventually will become comets. Each comet has its own orbit around the sun.

In space between the orbits Mars and Jupiter, a ring of rock material travels in space between the two planets, this region is named the asteroid belt. Sometimes the asteroids or comet particles are captured by the earth's gravity and burn up in earth's atmosphere. The burning rock falling from the sky is popularly called a falling star, shooting star or meteor. If the meteor doesn't burn up and lands of the Earth, they are referred to as meteorites.

At first, the Earth was much smaller than recent Earth. The planet increased to its current size as pieces of asteroids and comet fell to Earth during the first 2-3 million years.

After 100 million years, gravity separated the Earth into layers. The heaviest part (iron-nickel) became the core and the lighter one such as iron, magnesium and silicate became the mantle and crust. The lightest elements, such as gases formed the atmosphere.

After the earth cooled, water vapour began to escape and condense in the earth's early atmosphere. Clouds were formed and rain water fell on the primitive earth, cooling the surface further until it was flooded with water, to form the river, sea and oceans.

The main gas on Earth 4,000 million years ago was carbon dioxide. Only a small amount of oxygen was present. The first life has varied chemical composition, but mainly composed of water, carbon, hydrogen, oxygen and nitrogen.

The oldest microfossils are 3,500 million years old. It was the single cell which lives in rope of bead like colonies, which structure resembled cyanobacteria, which can photosynthesis. This bacterium is very important for oxygen production on the ancient earth.