Does freezing water have an odd property that makes life on earth possible?

Dear Cecil: I read somewhere that ordinary water has a peculiar characteristic that makes life on this planet possible. When most materials cool off they become denser and heavier, including water — except near the freezing point. It seems ice is less dense than water, so it floats. If it didn’t and sank instead, lakes and rivers would freeze solid in winter, killing all the fish and triggering a terrible ice age. Is this true? Do any other materials exhibit this abnormality or is water unique? William K., Burke, Virginia

Cecil replies:

It’s not unique, but few materials share this unusual (and for us, very fortunate) property. The only others I know of that expand when they freeze are cast iron and type metal, the lead alloy used in Linotype machines. But lotsa luck watering the begonias with those.

Like most things, water contracts as the temperature drops — until the mercury reads 40 degrees Fahrenheit. Then it starts to expand again. By the time water freezes, its volume has increased 10 percent. Since ice is less dense than water, it floats, forming a crust over lakes and streams and enabling life to go on below. Assuming you call this life.

Cecil Adams

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