Water is the stuff of life. We can't live without it, and neither can the rest of the food chain. The search for extraterrestrial life hinges on whether or not a planet or moon contains liquid water, but that assumes that any life off Earth is the same as Earth-based life. This week we'll take a look about what makes water so special and how it keeps all of us alive.
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| Water, the most abundant substance on Earth. Unless air is more abundant. |
Water is unique among all chemicals (yes, it's a chemical) because it is the only one found in solid, liquid, and gas states naturally on Earth. While ice and water vapor aren't basic requirements for life, they are key components of the water cycle. Water stored as snow and ice in the mountains is slowly released during the dry summers in the American west, meaning a steady flow in rivers throughout the year. Clouds made of water vapor transport precipitation over long distances. On top of that, ice and steam make modern life more convenient- think food storage and electricity generation.
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| Winter snow waiting for the spring melt, March 2016 |
Typically, solids are more dense than liquids, which in turn are more dense than gases. Water flips this around, as ice is less dense than liquid water. If you freeze a container of water, you'll notice that the ice fills more of the container than the water did. This is why your frozen pipes burst in winter. The expansion of water as it freezes is a visual of the density decreasing. Because ice is less dense than water, it floats. Because ice floats, it forms on the surface of lakes and other bodies. This allows aquatic life to survive. If water froze from the bottom up, everything would either freeze in place, or eventually be exposed on the surface.
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| Molecular structure of liquid water and ice (Mountain Empire CC) |
Water has adhesive and cohesive properties. Water molecules stick to each other (cohesion) and other substances (adhesion). Adhesion causes capillary action. This is the movement that is responsible for plants being able to absorb water in the ground through their roots, up the stem, and to the highest leaves. Cohesion also contributes to surface tension. Water molecules on the surface are more tightly packed and can resist pressure from outside forces. This allows objects to float. Water striders can stand on the surface because of surface tension.
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| Water strider striding water (National Wildlife Federation) |
Water has a high specific heat. Specific heat is the amount of energy needed to raise the temperature of a gram of water by one degree Celsius. Because it takes a lot of energy (1 calorie per gram) to heat water, it takes a lot of heat to boil water. Ocean life appreciates not being boiled. Water also holds onto heat it absorbs and releases it slowly, moderating Earth's temperature and making the seasonal changes gradual.
Water dissolves more substances than any other. The polar structure of the water molecule. The positive hydrogen end will attract negative ions, while the negative oxygen ends attract positive ions. Water's solvency is important for plants and animals to absorb nutrients, and for animals to flush waste from their bodies. Nonpolar substances like fats do not dissolve. That's where the saying "Oil and water don't mix" comes from. Less dense fats will float on top of water, and with some skill they can be separated.
Next time you take a drink, raise a glass in appreciation of water. Without it, your drink wouldn't be here and neither would you. This week's information comes from USGS and Mountain Empire Community College.