Until 4 degrees celsius water behaves normally, but as the temperature of water decreses below 4 degrees celsius, it suprisingly starts to expand.
Most of our Earth's surface is covered with water. Water has special chemical properties that differs it from the other liquids on earth. Other liquids freeze from the bottom up, but water freezes from the top down . As the temperature of liquids decrease, they begin to contract and their density increases. However, only water behaves strangely different.
Until four degrees celsius water behaves normally, but as the temperature of water decreses below four degrees celsius, it suprisingly starts to expand. By means of this abnormal property ice has a lower density than liquid water, and this facts makes it possible for the ice to float on the water.
If this was not the case, ice would sink to the bottom while the warm water would rise to the surface. Then warm water would also freeze and sink to the bottom as ice. This process would continue until all the water in the seas freeze and it would be impossible for life to exist in seas and rivers. Without life in water, all ecological system would fail to survive. So, "Then which of the favours of your Lord will you deny?" (Quran: 55/13)
Since ice floats on water, it forms a protective shield on the surface and keep the heat in the water below from escaping into the atmosphere. So, no matter how cold the air temperature is, creatures are able to survive under the protective ice layer. Moreover, there are fractures in the ice layer, so creatures such as penguins can go through the ice and hunt in the water.
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