The existence of liquid water, and to a lesser extent, gaseous and solid dosage forms on Earth is vital to the existence of life on Earth as we know it. The land is located in a residential area of the solar system, if it was slightly closer to or farther from (about 5%, or about 8 million km), the conditions that must be present simultaneously would be much less. Gravity of the earth allows him to retain the atmosphere. Water vapor and carbon dioxide in the atmosphere provides a temperature buffer (greenhouse effect), which allows you to maintain a relatively steady surface temperature. If Earth were smaller, thinner atmosphere allows extreme temperatures, thereby preventing the accumulation of water, except the polar ice caps (as on Mars). Surface temperature was relatively constant through geologic time, despite different levels of incoming solar radiation (insolation), indicating that the dynamic process of regulating the temperature of the Earth through a combination of greenhouse gases and surface or atmospheric albedo.
This proposal is known as the Gaia hypothesis. The state of water on the planet depends on external pressure, which is determined by gravity of the planet. If the planet is massive enough water on it can be hard, even at high temperatures, due to the high pressure caused by gravity. There are various theories about the origin of water on Earth. Water ice is present on: Land – mostly ice sheets of polar ice caps on Mars, Titan Enceladus Europa Comets and comet population source (in the Kuiper belt and Oort cloud objects). Water ice may be present on the Moon, Ceres, and Tethys.
Water and other volatiles are likely to constitute a significant part of internal structures Uranus and Neptune. Water is the most common solvent in the world, largely determines the nature of the Earth's chemistry as a science. Much of the chemistry, in its origin as a science, began just as the chemistry of water solutions of substances. It is sometimes regarded as the ampholyte – and acid and base at the same time (H + cation anion OH-). In the absence of foreign substances in the water the same concentration of hydroxide ions and hydrogen ions (or ions hydronium), pKa ca. 16. By itself, water is relatively inert under normal conditions, but its highly polar molecules solvated ions and molecules to form crystalline hydrates. Solvolysis, especially hydrolysis, occurs in animate and inanimate nature, and is widely used in chemical industry.