Irving Madden, age 14, of Portland, Ore., for his question:
WHAT ARE THE HYDROSPHERE AND LITHOSPHERE?
The land on earth is called the "lithosphere." We call the earth's water the "hydrosphere." These scientific names aren't used very often.
A bit more than 70 percent of the earth's surface is covered with water. Almost all of this water is located in oceans. Even though there is so much water on our planet, most of us think of the land areas when we think of the earth, even though we know that less than 30 percent of the surface is made up of land.
The average depth of the hydrosphere, which includes our lakes and seas, is about two and a half miles. In some parts of the Pacific Ocean, the hydrosphere goes down to a depth of six miles.
In many ways, the hydrosphere resembles the earth's atmosphere because of its pressure and temperature changes at different depths. By lowering thermometers into the sea, oceanographers have discovered that even in tropical oceans, the temperature at great depths can be just a few degrees above freezing.
The chemical content of the hydrosphere does not change with variations of temperature and pressure although it does vary according to whether the body of water is fresh or salt water.
The earth's land, or lithosphere, rises to an average height of 2,757 feet above the level of the oceans.
The largest bodies of land are called continents. Surfaces vary on the various continents from green, lush valleys to high, rocky mountains where almost nothing grows.
The earth's animals and plants live on the earth's surface or close to the surface. The area where life is found is another scientific name that isn't used too often: the area is called the earth's biosphere.
The earth's crust is made up of 46.6 percent oxygen, 27.7 percent silicon, 8.1 percent aluminum, 5.0 percent iron, 3.6 percent calcium, 2.8 percent sodium, 2.6 percent potassium, 2.0 percent magnesium and 1.6 percent of other elements.
Water is made up of hydrogen and oxygen. When these elements are by themselves, they are gases, but when two atoms of hydrogen combine with one atom of oxygen, a compound called water is formed.
Water can appear as a frozen solid, a liquid or as a misty gas.
When the hydrosphere and the lithosphere combine, you can rightly think of the earth as looking like a giant ball spinning in space. It takes an astronaut about 90 minutes to circle the earth in his space craft, and it takes almost two days for a jet airplane to cover the same distance.
Air surrounding the earth extends out as far as 1,000 miles above the surface. The air is called the atmosphere.