The Earth was probably formed several million years after a massive explosión took place in space. The explosion created an immense cloud of gas and dust particles. Geologists think that the particles collided with each other, joining together to form huge clumps of melted matter which eventually became the present-day planets.
It is thought that the newly-formed Earth was incredibly hot, with a sea of molten rock on the surface. About 4,000 million years ago, the Earth slowly began to cool down and separate into different layers. The heaviest matter sank to form the core, or central part, of the Earth, but still remained incredibly hot. The less dense matter formed layers around the core. At the surface, the molten matter cooled down sufficiently to form a solid, rocky crust, which Scientists believe was covered with many volcanoes.
The first continents were probably formed from molten rock which flowed onto the surface through volcanoes, cooled on the surface and made the crust thicker. Oceans may have appeared in lower-lying areas, as tiny droplets of water condensed onto the cooling surface from gases escaping through volcanic eruptions. The Earth's first atmosphere was probably formed by these volcanic gases.
