WWC - An Overview of Water Lesson

 

An Overview of Water

Over 70% of the Earth's surface is covered in water, and over 97% of that water is found in the oceans and other marine environments that blanket the continent. Of the remaining 2.5% that is fresh, 2/3 is frozen in glaciers and icecaps - at high latitudes as well as high altitudes - and nearly 1/3 is underground. Of the 0.025% of Earth's water that is fresh and found at the surface, 2/3 is in permafrost, and the remaining 1/3 is either found in lakes, rivers, and streams on the surface of the continents, or in the atmosphere. So, only 0.75% of ALL of the water on Earth is available for human consumption in the form of surface or underground water, and its distribution across the Earth's surface is not always equitable; some areas have more freshwater than others.

The average depth of the oceans is over 2 miles deep. However, given the relatively large size of the Earth, there's really not that much water covering it. In the accompanying image, the largest of the three spheres represents ALL of the water in, on, or surrounding Earth (salt and fresh). The middle-sized sphere represents all of the freshwater on Earth (roughly 3% of the larger sphere), and the smallest sphere (over Atlanta) represents all of the fresh water found on the surface in lakes, rivers, and streams.

Water has many interesting properties that help support life on Earth. Several of these properties also come into play with regards to the non-living world. Because water is a polar molecule, it readily combines with other polar molecules and charged particles. Nicknamed "the universal solvent", water is capable of dissolving more substances on Earth than any other liquid. Because of this, water on Earth is rarely "pure"; it almost always contains elements and molecules with which it comes into contact.

Unlike most substances, water is less dense as a solid than it is as a liquid. This is the reason that ice floats in liquid water, as opposed to sinking to the bottom. The reason for this is due to the molecular arrangement of water molecules when they freeze; as they become locked together, they form a regular structure called a lattice that actually spreads the molecules farther apart from each other than when they existed in a liquid state. This is important because it means that ice is not only less dense than liquid water, but it also occupies a larger volume (if you've ever left a full container of water or other water-based drink in the freezer for too long, you may have already learned this). This property will prove to have a profound effect on the shaping of the Earth's surface.

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IMAGES CREATED BY GAVS OR OPENSOURCE