The three states of water - "the
water cycle"
Water (H2O) exists as all three states on Earth. It is solid in the polar ice caps and glaciers, liquid in the oceans, lakes, rivers, underground artesian basins and clouds, and as a gas in the atmosphere. The three states of water are named, unlike any other substance.
Icebergs and polar ice sheets melt in summer and freeze in winter because they float on the surface instead of sinking to the ocean floor. They also absorb heat energy on melting and releasing that energy on freezing, thus helping to moderate the Earth's climate. The
weather patterns that make our world a place that we can live in are the
product of the melting and freezing of this sea ice. If ice did not float,
it would sink and the oceans would be solid ice with a layer of liquid
water. The Earth would also be a much less windy and colder place. Liquid - water The Earth is in a unique position within the Solar System being just far enough away from the Sun to allow liquid water to exist in significant quantities. If it were closer, all water would be gas; if it were further away, all water would be solid ice. Clouds form when gaseous water vapour in the atmosphere is cooled and droplets of water form. It is these droplets of water that we see as fog and clouds.
Pure steam exists at temperatures above 100°C at sea level and 1 atmosphere air pressure. At lower atmospheric pressures - altitudes above sea level - water boils at less than 100°C, hence, steam can exist at temperatures less than 100°C at higher altitudes. At lower temperatures, gaseous water exists as a mixture in air. Water evaporates from surface liquid water and mixes with the air; this is measured as humidity. Air humidity is another very important modifier of climate. The increased humidity of the air in the tropics keeps temperatures down in the 30's°C, unlike desert regions where the drier air allows temperatures of 40°C to 60°C to be reached. The greenhouse effect The
water cycle
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