The Chemistry of Planet Earth

Earth Chemistry for Earth Day

Our Earth is the only planet that can initiate and sustain life-forms, with an atmosphere containing two chemical elements, 78% of nitrogen and 21% of oxygen at an average temperature of 15 degrees Celsius and with two-thirds of its surface covered by ocean. 

A chemical element is a basic substance found in nature. It cannot be broken down into simpler substances by using ordinary chemical processes. The elements are the building blocks for all other substances. When they are combined with other elements the result is called a compound. For example, water is a chemical compound of the elements oxygen and hydrogen.

Nature has 92 chemical elements, and more than 20 additional ones have been created artificially in laboratories. Some elements, including nitrogen – the major component of air – are present in great abundance. Some are quite rare.

Major chemical elements of the Earth

(including those found in Earth's crust, mantle and core)

1.  Iron (Fe) - 35%
2.  Oxygen (O) - 28%
3.  Magnesium (Mg) - 17%
4.  Silicon (Si) - 14.3%
5.  Sulfur (S) - 2.7%
6.  Nickel (Ni) - 2.7%
7.  Calcium (Ca) - 0.6%
8.  Aluminum (Al) - 0.4%
9. Others elements - 0.6%

Iron (Fe). It is the first most abundant chemical element in the Earth's depths, the second most abundant metal and the fourth most common chemical element in the Earth's crust. Iron was used by early people. Its chemical symbol, Fe, is taken from the Latin ferrum. The name iron is from the Anglo-Saxon iren or isern. About 5 percent of the Earth's crust is composed of iron. The metal is chemically active and is found in nature combined with other elements in rocks and soils. Both plants and animals also contain very small amounts of iron. In the Earth iron occurs mainly in iron-oxide ores. One of these ores is lodestone, or magnetite, named for its property of magnetism. Hematite is the most plentiful ore, but it contains less iron than magnetite. Iron, alloyed with nickel, is also found in meteorites.

Oxygen (O). It is the most abundant chemical element on Earth (chemical symbol O), and it is essential to all the planet's life forms. As the gas O₂ it is in the lower atmosphere in the air that is breathed, and in the upper atmosphere as ozone (O₃) it shields the Earth's surface from the sun's harmful ultraviolet rays. In combination with other chemical elements, it forms hundreds of thousands of compounds, making up by weight almost half of the rock and sand in the Earth's crust. In its free state, oxygen is a gas without color, odor, or taste. Oxygen is very active chemically and combines readily with nearly all other elements; these elements are then said to be oxidized.

Magnesium (Mg). The lightest common metal is magnesium. It weighs one-third less than an equal volume of aluminum and is the eighth most abundant element in the Earth's crust. As a result, it has found extensive use in the aerospace industry. However, because the pure metal is not very strong, however, alloys have been developed to improve its hardness, tensile strength, corrosion resistance, and ability to be cast, welded, and machined. These alloys are used in making parts for aircraft and spacecraft, rocket components, automotive equipment, light machinery, portable tools, and household appliances. Magnesium does not occur uncombined, but there are many compounds of magnesium in nature. Many soils and rocks contain magnesium compounds. Two of the most common minerals containing magnesium are magnesite (magnesium carbonate) and dolomite (calcium magnesium carbonate).

Silicon (Si). This non-metal is the second most abundant element on Earth. is the nonmetal silicon, which makes up about 28 percent of the Earth's crust. It occurs only in such combined forms as silica (silicon dioxide) and silicate rocks and minerals. The most common form of silica is quarts, which includes sand and flint. Silicates are salts in which silica is combined with oxygen and other elements, such as aluminum, magnesium, calcium, sodium, iron, and potassium. It has a strong affinity for oxygen. Pure silicon can be obtained by breaking down its combined form.

Sulfur (S). Used in thousands of products and processes, it is a critical raw material in industrial countries. Sulfur is a nonmetallic element, yellow in color and similar to oxygen in its chemical behavior. Sulfur burns readily with a blue flame, which earned it the name brimstone, or “burning stone.” It one of the elements necessary to life, found in many animal and vegetable substances, especially proteins. The bad smell of a rotten egg is due to hydrogen sulfide. It is the sulfur in eggs that tarnishes silver so quickly, forming the black compound silver sulfide. Sulfur exists in nature both in its native, uncombined form and in compounds. Sulfur can be extracted commercially from pyrites.

Nickel (Ni). This metallic chemical element was given its name from Kupfernickel, after the German “Old Nick” and his mischievous imps. The reason was that early chemists had difficulty identifying its unfamiliar properties. One of the most useful metals, nickel makes up 0.007 percent of the Earth's crust. It is silvery, lustrous, hard, malleable, and magnetic. Pure nickel is used in coatings (nickel plate) on other metals to embellish or protect them. Nickel alloys have numerous domestic and industrial applications. Copper, zinc, and nickel form a metal known as German silver, used to make tableware and as a base for silver-plated ware.

Calcium (Ca). It is the fifth most abundant chemical element in the Earth's crust. It is classified as an alkaline earth metal. Calcium does not occur free in nature. It is found in many chemical compounds, one of the most familiar of which is the main constituent of limestone. There are many important industrial uses for calcium. It is used as a deoxidizer in the refining of iron, steel, copper, and copper alloys. It is a constituent of several lead and aluminum alloys. It is also used in extracting certain metals from their ores. Calcite is a crystalline form of calcium carbonate, and Iceland spar, one of its varieties, has the power to produce double refraction of light. The carbon dioxide in water helps dissolve calcium carbonate, so that in limestone caves the evaporation of dripping water produces stalactites and stalagmites.

Aluminum (Al). This silvery-white chemical element aluminum ranks among the most industrially important metals. Except for magnesium and beryllium, it is the lightest structural metal and is highly ductile, capable of being cast, rolled, stamped, drawn, machined, or extruded. It is also corrosion resistant, heat reflective, and an excellent conductor of electricity. Although aluminum is soft and has relatively low tensile strength in its pure form, it can be made much harder and stronger if alloyed with copper, magnesium, or zinc. Aluminum is more widely used than any other metal except iron and steel. Pure aluminum metal is utilized in electronic components, reflectors, utensils, and fine jewelry. It is also converted into a powder that can be mixed with other substances to produce metallic paints, rocket propellants, flares, and solders. Aluminum alloys have a far wider range of commercial applications, including the manufacture of appliances, food and beverage packaging.

Prominent information about the Earth's chemistry include the following:

• The evidence of the Earth's chemistry is derived from analyzing densities with the help of earthquake waves, and from studying stars, meteorites, as well as other planets.


• The bulk of the Earth's chemical elements is made from iron, oxygen, magnesium and silicon.


• The Earth's crust has 82 stable elements and a few unstable ones, mainly the radioactive. Among the stable elements, there are some, such as oxygen and silicon, that are very abundant, while others - the metals ruthenium and rhodium, for example, are extremely rare.


• The crust is made mostly from oxygen and silicon, with aluminum, iron, calcium, magnesium, sodium, potassium, titanium and traces of 64 other elements.


• The Earth's upper mantle is iron and magnesium silicates. The lower is silicon and magnesium sulfides and oxides.


• The Earth's core is mostly iron, with a little nickel and traces of sulfur, carbon, oxygen and potassium.


• Chemical elements that combine easily with sulfur, such as zinc and lead, spread through the mantle.


• Chemical elements that combine easily with iron such as gold and nickel, sank to the core.


• Some heavy chemical elements, such as uranium, ended up in the crust as they easily make compounds with oxygen and silicon.

Happy Earth Day!   

Resources:

• Encyclopædia Britannica Online Library Edition. Accessed April 22, 2013.
• Farndon, John.  4000 Things You Should Know. (2000)  Miles Kelly Publishing.  Essex.