If ice cubes didn’t float, marine life couldn’t survive

Here in western Colorado, we hear about it all the time, because it is scarce.

But, ironically, as dry as our climate is, most of the water that supplies the Southwestern United States passes through our area in the form of the Colorado River.

In school, we hear that most of the human body is composed of water. This seems odd when you think about those dry bones and that stringy muscle that we are made of. (OK, but it’s not so hard to believe when we look at that “jiggly” area around our belly.)

So what is this stuff we call water?

Even grade school students will tell you that water is “H-2-O” — a molecule made of two hydrogen atoms and one oxygen atom. This is interesting, because hydrogen and oxygen are gases, which combine to make a liquid.

But this is not just any liquid.

We routinely encounter water in all three of its physical states — gaseous, liquid and solid. For the gaseous state, think of steam or water vapor.

The liquid state is what we see most of the time, in rivers, lakes, oceans and what comes out of the faucet. And the solid state is one of our favorites during the winter — ice and snow. (And it’s also a nice cooler for your summer iced tea or lemonade.)

We take these manifestations of water for granted, but can you think of any other material that we encounter in all three common physical states — gas, liquid, and solid? I can’t.

This easy transition between physical states gives water mobility — it evaporates from one area of Earth, such as the ocean, and condenses somewhere else, such as a mountaintop, in the form of rain or snow. We would have no rivers, lakes or glaciers without this mobility.

On the atomic level, when you combine those two hydrogen atoms with that one oxygen atom, they don’t quite line up in a straight line — it’s more of a “V” shape. This gives every molecule a little bit of an electromagnetic “pole,” which makes them stick together a little bit.    It means that, if you put a bunch of water molecules together, they don’t ignore each other, but they pull toward each other. This “stickiness” or pulling results in something called surface tension.

Surface tension is what makes water form into droplets. Without surface tension, there would be no rainbows, which are caused by sunlight bouncing (or “refracting,” to use the technical term) off water droplets that condense out of the atmosphere to form rain.

Surface tension allows insects that are heavier than water to sit on the surface of a pond.

Without it, entire evolutionary lines of development would not have occurred. And surface tension — that “stickiness” between water molecules — is also the cause of something called capillary action, which allows tiny columns of water to be pulled up the stems of plants and the trunks of trees.

Without this effect, we would live in a world where plants probably could grow no higher than the surface of a lake or the ocean.

Oh, and by the way: Almost all elements and compounds shrink as they cool. They take up less space as they go from gases to liquids to solids. Water shrinks, too, until it gets to the point of turning from a liquid to a solid (i.e. “freezes” from water to ice).

Then it does exactly the reverse of what would be expected. It actually expands slightly.

This makes ice less dense, or lighter, than liquid water. And if ice is lighter than the liquid material it comes from, it will float on the surface (which we have all seen — ice cubes float, they don’t sink).

If water was like everything else and shrank as it froze, ice would sink to the bottom. If ice sank instead of floating, when freezing temperatures occurred, ice would sink to the bottom of ponds and lakes and oceans first, and would continue doing so until the entire body of water froze solid.

It would not take severe cold for this to happen — it could happen at a temperature of just less than 32 degrees Fahrenheit, as long as it stayed at that temperature long enough.

With a solidly frozen body of water instead of an insulating layer of ice on top of the body of water, marine life as we know it could not survive.

Just a few things to ponder the next time you have a nice, cool drink of water here in the desert.


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