Ice
Ice is the solid form of water, created from covalently bonded oxygen and hydrogen atoms. It forms when liquid water reaches a temperature of zero degrees Celsius (32 degrees Fahrenheit). Ice exists in various forms across Earth and beyond, including glaciers, permafrost, and interstellar ice. A unique property of ice is its lower density compared to liquid water, allowing it to float—this characteristic has crucial implications for aquatic ecosystems, as many organisms thrive beneath ice-covered waters. Ice is commonly found in the cryosphere, encompassing regions where temperatures allow for its formation, and plays a significant role in Earth's moisture distribution, particularly as a source of fresh water from melting snow.
The presence of ice also influences economic activities, impacting transportation, weather conditions, and recreational sports such as skiing and ice skating. Historically, ice was harvested and transported for preservation and culinary uses before modern refrigeration became commonplace. The debate over why ice is slippery encompasses several theories, including the effects of pressure, friction, and the molecular arrangement of surface water. Overall, ice is an essential component of both ecological systems and human activities, shaping various aspects of life on Earth.
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Ice
Ice is the solid form of water, the compound formed from covalently bonded oxygen and hydrogen atoms. Liquid water transforms into ice at zero degrees Celsius (thirty-two degrees Fahrenheit). Ice can be found on the surface of Earth wherever temperatures permit. It can also be found within and beyond the solar system, where it is referred to as interstellar ice.
One unusual property of ice is that while in a solid state, it is slightly less dense than in its liquid form. As a result, ice floats on water rather than sinking to the bottom. This has profound implications for Earth’s ecosystem. Many species of algae and similar aquatic life forms have evolved to exist in the sheltered regions of the sea beneath a layer of floating ice, which would not exist without the lower density of ice that allows it to float. Some scientists have even suggested that if the density of ice were greater than liquid water, lakes and oceans all over the world would freeze from the bottom up.
Background
The water molecules that make up ice are arranged in an orderly structure. Ice typically appears blue or greenish blue, depending on its thickness, because it absorbs the red light in the spectrum. Much of Earth’s surface is covered in ice either seasonally or throughout the year. Areas where the temperature permits the formation of ice are collectively referred to as the cryosphere.
The ice of the cryosphere contains a significant portion of Earth’s moisture; in many areas, melting snow is an important source of fresh water. Ice can be found in almost every part of the biosphere: in the ocean, where it occurs as drift ice if floating, anchor ice if attached to the sea floor, or fast ice if attached to the shore; in the air, floating as minute crystals or falling as snowflakes or hail; on land, in the form of glaciers or as the result of snow accumulation or precipitation that has frozen after falling; and below the soil, as permafrost.
Overview
Ice plays a major role in the economy, both directly and indirectly. Its indirect effects can be felt in the way it impacts travel and transportation. Weather that produces ice makes travel difficult or impossible. Icy roads are dangerous to drive on, and freezing rain can gather on the wings of airplanes, making them too heavy to fly. In addition, many sporting and recreational events, such as skiing, ice skating, and ice hockey, rely on the presence of ice. Commercial settings also rely heavily on ice for storing perishable goods, as an ingredient in concrete, and in the production of some chemical compounds.
In the past, the production, transportation, and storage of ice was a complex industry. Ice was harvested from areas where it naturally occurred, such as in mountainous regions, and then transported with enough speed and proper packaging to prevent it from melting on the way to its destination. It then had to be stored in a facility that would maintain a sufficiently low temperature until it was needed. In the days before electricity, air conditioning, and refrigeration, this process was extremely difficult. There are records dating back to 400 BCE that describe a Persian system whereby ice was brought down from the mountains and stored underground. As late as the nineteenth century, ice was still being imported to England from Norway.
Ice, or the lack thereof, has also had an impact on culinary development around the world. In many locations, ice was so difficult to come by that its availability for food preservation could not be relied on. For this reason, alternative forms of preservation, such as pickling, spicing, canning, salting, and smoking, were developed. Once ice became available to more people in the late nineteenth and twentieth centuries, frozen desserts such as ice cream and popsicles became wildly popular, and ice was used to preserve food during transportation. Perishable items, such as fruit grown in warmer climates, could be shipped across states and countries and sold in regions far removed from where they were produced.
An often-debated point about ice is the question of why it is slippery. Many believe that the slipperiness is caused by pressure. When an object comes in contact with ice, the resulting pressure creates an increase in temperature, which would then cause the surface ice to melt, making the surface slick. Others have suggested that ice becomes slippery not because of pressure but because of friction, which melts a thin layer of ice. A third theory is that water molecules at the surface of ice are less rigidly positioned than those below the surface, causing them to behave more like a liquid than a solid.
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