The outermost surface of the Earth is called the lithosphere, or crust. This rigid layer contains both the oceans and landmasses. Most elements are found in only trace amounts within the earth’s crust, but several are abundant.

There are 92 naturally occurring elements, from hydrogen to uranium, and the earth’s crust contains nearly all of them.

Recall that an element is a substance unable to be broken further by chemical means. The atoms of a particular element have the same number of protons in the nucleus. On the periodic table, elements are listed by a symbol, such as O for oxygen.

When two or more elements combine, a compound is formed. An example is silicon tetraoxide, SiO₄, a compound of oxygen and silicon.

Oxygen, O₂, is by far the most abundant element in earth's crust at 46.6 percent, nearly half of the mass of the crust.

Oxygen is a highly reactive element capable of combining with many other elements to form compounds. It readily combines with silicon (Si) to form silicate minerals or with iron (Fe) to form various iron ore compounds.

Silicon, Si, is a metalloid, the second most abundant element in the Earth's crust and accounts for 28 percent of the crust’s mass.

Combined with oxygen, it forms silicate materials, such as silicon dioxide, SiO₂. Sand consists mostly of silicon dioxide, and quartz and other crystalline rocks are formed from other silicate materials. Silicon is also an essential material in the manufacture of electronics and computer chips.

Aluminum, Al, is the third most common element in the Earth's crust with 8.1 percent of the crust’s mass.

All the earth's aluminum is combined with other elements to form compounds, and it is never found as a lone element. Aluminum oxide (Al₂O₃), aluminum hydroxide (Al(OH)₃) and potassium aluminum sulfate (KAl(SO₄)₂) are common aluminum compounds. Aluminum and aluminum alloys have a variety of uses from kitchen foil to rocket manufacturing.

Iron, Fe, is the fourth most common element in the Earth’s crust, accounting for over 5 percent of the crust’s mass.

Iron is mostly obtained from the minerals hematite and magnetite. Of all the metal refined currently, 90 percent is iron, mostly to make steel, an alloy of carbon and iron. Iron is also an important nutrient in the human body.

Calcium, Ca, is the most abundant alkaline earth element in the Earth's crust and makes up approximately 3.6 percent of the earth’s crust.

This fifth most abundant element in the earth’s crust is a reactive element that readily forms compounds with oxygen and water and is not found free in nature. Manufacturers use calcium compounds in many applications including gypsum board (drywall), chalk and toothpaste.

Sodium, Na, is the most abundant alkali metal in earth’s crust and composes 2.8 percent of the earth’s crust.

The sixth most abundant element is best known as part of the compound that makes table salt, sodium chloride (NaCl). Sodium is highly reactive and not found as a lone element. It is an ingredient in many useful compounds such as baking soda, caustic soda and borax. Sodium lamps produce a bright yellow-orange light and are widely used to light roads and parking lots.

Potassium, K, makes up about 2.6 percent of the Earth's crust and is the seventh most common element.

This extremely reactive element is never found free in nature and forms numerous compounds. Some of potassium’s compounds are used in the manufacture of fertilizer, soaps, detergents and some types of glass.

Magnesium, the eighth most abundant element in the earth’s crust, comprises approximately 2.1 percent of the crust’s mass.

In nature, magnesium is only found in compounds and not as a lone element. Magnesium has many applications: In the home, it may be used as an antacid and laxative, and it is the essential ingredient of Epsom salts. In industry, magnesium-aluminum alloy is used in the construction of aircraft and other applications where strong, light metals are required.