Page 28 - Curriculum Visions Dynamic Book

Water on the Earth
Although we may swim in warm surface ocean
waters, most of the ocean is cold. In fact, the average temperature of the world’s oceans is 4°C, which also happens to be the temperature at which water is most dense. The temperature is not far above freezing point, so we barely avoid being a frozen world.
As described in the atmosphere section (pages 22–27), the Earth’s water exists as solid, liquid, and
gas. Almost all of it is liquid water in the oceans, with small amounts locked up as ice caps and ice sheets, and a tiny gaseous proportion circulating between oceans, atmosphere, and land.
The water cycle (page 29) stretches both into the air and into the rocks. Circulating water vapor reaches up to the top of the troposphere at 15 km and also percolates 5 km down into rocks.
The water cycle is powered by sunlight. About a third of the Sun’s energy that reaches us is used up fueling the water cycle.
condensation The change of state from a gas or vapor to a liquid.
convection The circulating flow in a fluid (liquid or gas) that occurs when it is heated from below.
evaporation The change in state from liquid to a gas.
lava Hot, melted rock from a volcano. Lava flows onto the surface of a planet and cools and hardens to form new rock.
percolate To flow by gravity between particles, for example, of soil.
sedimentary Rocks deposited in layers.
solar radiation The light and heat energy sent
into space from the Sun.
troposphere The lowest region of the atmosphere, where all of the Earth’s clouds form.
water cycle The continuous cycling of water, as vapor, liquid, and solid, between the oceans, the atmosphere, and the land.
water vapor The gaseous form of water. Also sometimes referred to as moisture.
 Because water can occur as ice as well as liquid and gas, it can evaporate from the oceans, make clouds, fall as snow, and be compacted into ice. Ice is one of the most powerful of all eroding agents, as seen here at the Malaspina Glacier, Alaska.
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