THE WATER CYCLE.

Water exists on Earth in three States: liquid, solid (ice, snow) and gas (water vapour). Oceans, rivers, clouds and rain are in constant change: the surface water evaporates, the water of the clouds precipitates, rain seeps from the Earth, etc. However, the total amount of water on the planet does not change. Circulation and conservation of water on Earth is called hydrological cycle, or the water cycle. When it was formed, approximately four thousand five hundred million years ago, Earth had water vapor inside.
In the beginning, was a huge ball in constant merger with hundreds of active volcanoes on its surface. Magma, gases with water vapor-Laden, emerged to the surface thanks to the constant eruptions. Then the Earth cooled, the water vapour is condensed and again fell to the ground as rain.