Like all the other planets in the Solar System, the Earth is thought to have formed at the same time as the Sun, some four and a half billion years ago. Colliding asteroids formed the beginnings of an early planet, and its gravitational pull continued to attract solid material towards it.
As the Earth grew in size, so the strength of its gravitational field increased. More and more collisions took place with greater amounts of energy. This made the Earth's surface heat up, to the point where it began to melt. This melting resulted in the layered structure we see within the Earth today, with the formation of a core, mantle and crust.
The separating out of the structure of the Earth was probably the most significant event in the formation of the planet. Not only did it lead to the creation of the crust and the continents, but also the atmosphere and the oceans.
The Earth looks very different today to how it once did. The surface used to be littered with active volcanoes and, with no ozone layer, the atmosphere had no protection from the Sun. Over millions of years, though, the planet cooled and the water in the atmosphere settled to form the oceans in which life began.
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