Hydrosphere

This unit was all about the water on Earth! We started off our year learning about the water cycle, water distribution, freshwater, ocean water, water pollution and quality, the properties of water, and how some people do not have access to clean water.

Below is a quick summary of the unit:

• Water covers approximately 71% of the Earth’s surface (USGS). Most of this water (97%) is not drinkable because it is saltwater. The majority of freshwater (3%) exists in ice caps, glaciers, and oceans. 77% of the freshwater is frozen. Of the 23% that is not frozen, approximately a half of a percent is available to supply living organisms with what they need to survive. The availability of water varies with local geography and allows humans to utilize water as a resource.

• Water is the only substance on Earth that occurs naturally as a solid, a liquid, and a gas. It is often referred to as ‘the universal solvent’ because so many other substances dissolve in it. This characteristic is one reason that the water encountered on Earth is rarely pure.

• The sun drives the entire water cycle and is responsible for its two major components: condensation and evaporation. When the sun heats the surface of water, it evaporates and ends up in the atmosphere as water vapor. It cools and rises, becoming clouds, which eventually condense into water droplets. Depending on the temperature of the atmosphere and other conditions, the water precipitates as rain, sleet, hail or snow.