Summary
Earth is the third planet from the Sun. Scientists believe that 4,6 billion years ago, a mass of boiling rocks that revolved around the Sun turned into a ball of liquid rock.
It then cooled slowly thus forming a hard crust on the outside.
Sometimes, the hot gasses and liquid rock actually broke through the crust in many places. This is the way mountains were formed and they, in turn, cut deep trenches into the surface of our planet, that later constituted ocean beds.
There is geological evidence that shows the vaporisation of water present in the atmoshpere while the Earth was cooling down.
Rivers and oceans were formed as a result of violent storms and heavy rain. Oxygen appeared on the planet when plants began to grow in the seas and started to produce it by photosythesis.
It was after this process that the first animals appeared. At first, they lived in the sea but as a result of the development of bigger animals, they gradually came out of the water. The first ones were fish that evolved into creatures that had lungs.
