![Reflections in Nature](/uploads/4/1/4/0/41406429/2719303.jpg?387)
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In pure water, ice begins to form at 32 degrees Fahrenheit; however, water that contains impurities will not freeze until lower temperatures are reached. Due to the salt, sea water begins to freeze at 27 degrees Fahrenheit. Ice crystals expel brine as salt water freezes, leaving the ice pure. The Eskimos get their fresh water from sea ice.
Scientists tell us that our polar ice caps are melting, and if this continues, the oceans will rise. Ice covers ten percent of the earth, with eight percent on land. Ice glaciers contain most of the ice on solid ground, which means that eighty percent of the world’s freshwater is locked up in ice. These ice glaciers are large and heavy, with their weight reaching its maximum 20,000 years ago. The glaciers’ weight has pushed the ground beneath them as far down as half a mile. After each glacial period (as the glaciers are retreating), the removal of weight from the depressed land leads to a slow uplift or rebound of the land. Today, this rebound is affecting both Europe and North America; however, this rebound is very slow and could continue for another 10,000 years.
This glacier adjustment is now being referred to as glacial isostatic adjustment, which involves loading and unloading of the glaciers and the rebound movement and downward movement of the land beneath the glaciers. Some scientists feel that the glaciers are affecting sea levels; earth’s gravity fields; earthquakes and changes in the earth's rotation. A pond or lake will freeze over from the top down. Once the ice forms it works as a blanket to insulate the water from the colder air. If it is windy when the water freezes, the ice will be rough and either a white or gray in color. If the wind is calm as the water freezes, the ice will be smooth and transparent.
Streams and rivers do not freeze as fast as ponds and lakes. The moving water slows the ice formation and the ice will not be as thick over moving water or near a spring. Ice is usually thinner near the middle of ponds and lakes than it is near the edge. In the spring, sunlight will warm the ground, which causes the ice near the shore to melt first or become less thin.
The ice on a river is weaker than lake ice due to the river’s current. Clear water freezes faster than water containing either chemicals or pollutants. Waterfowl and schools of fish prevent ice formation; structures through the ice (such as bridges, piers, etc.) weaken the ice because these structures absorb heat and the ice surrounding a beaver house could be thin, even on the coldest of days because of the beaver's activity.
On some mornings, we have a frost, which is nothing more than frozen dew. At night, the ground cools faster than the air above the ground. When moist air contacts a freezing surface, such as grass, tree branches or the bare ground, we have a frost.
In the far north, frozen ground that never completely thaws is called permafrost, which can be thousands of feet deep in places.
We also have ice in our sky in the form of hailstones, created by water being swept up to colder levels of the atmosphere. Our upper atmosphere contains many ice crystals that reflect solar radiation, keeping the planet from becoming too hot or too cold. Some scientists feel that most of the earth’s water has accumulated over billions of years as comets shed some or all of their ice in our atmosphere.
Our bodies are about 60 to 75 percent water. Frostbite can occur when the water freezes in our tissues. Although we may not like ice on our roads and sidewalks, ice is a very important part of our environment.