Water Facts.
Unlike most other liquids, when water freezes, it expands and becomes less dense. Most other frozen liquids are denser than their melted selves and thus sink. If it sank, ice, being unable to melt because of the insulating layer of water above it, would slowly fill up lakes and oceans in cold climates, making sea life in those parts of the world a challenging prospect.
While other substances form liquids, precious few do so under the conditions of temperature and pressure that prevail on our planet's surface. In fact, next to mercury and liquid ammonia, water is our only naturally occurring inorganic liquid, the only one not arising from organic growth.
At sea level, water boils at 212°F, but thousands of feet down in the ocean, the pressure can keep water liquid at over 650°F as in deep ocean hydrothermal vent.
"Water is probably the best solvent in the universe," says Jeffrey Bada, a planetary scientist at the Scripps Institution of Oceanography in La Jolla, Calif. "Everything is soluble in water to some degree." Even gold is somewhat soluble in seawater. (Before you get any ideas about extracting gold from the oceans, I should add that, according to Bada, the value of dissolved gold in a metric ton of seawater comes to about $0.0000004).
The biochemical reactions that sustain life need fluid in order to operate. In a liquid, molecules can dissolve, and chemical reactions occur. And because a liquid is always in flux, it effectively conveys vital substances like metabolites and nutrients from one place to another, whether it's around a cell, an organism, an ecosystem, or a planet. Getting molecules where they need to go is difficult within a solid, and all too easy within a gas-vapor-based life would go all to pieces.
Water is the only element that is naturally found in all three states. Ice (solid) in the polar regions, Vapour (gas) in the air, and liquid on the ground. Actually, water is the only molecular substance to exist on Earth in all three states without human influence.
