Page:Illustrated Astronomy.pdf/43



PRESENCE OF LIQUID WATER

More than 70 % of the terrestrial surface is covered in water. In fact, the Earth is the only planet in the Solar System that has the three phases of water on its surface (solid, liquid, and gas).

Some of the properties that make water an essential element for life development on Earth are: it is an excellent solvent, it provides suitable conditions to many chemical reactions, and it allows the transfer of substances between cells and their environment. Also, the heat capacity of water -that is the amount of energy required to increase one Celsius degree- is very high, which means that in comparison with other elements such as rocks or metal, water takes more time to heat, remaining the surface temperature of the planet stable with slight variations between day and night. • • • 43