Geochemistry is a branch of science that uses chemistry to study Earth’s history and the materials that make up the planet. Geochemists study the natural processes that distribute the chemical elements, their isotopes (different forms), and their compounds throughout Earth. The scientists also study how chemicals behave in the environment. Geochemists observe how chemicals move among the air, soil, and water. They also study how human activities—such as agriculture, manufacturing, mining, and transportation—change the chemical composition of the environment.
Geochemists use a variety of methods and instruments to determine the chemical makeup of materials, such as rock, water, sediment, and soil. Some methods are as simple as dripping acid onto a rock. If the rock fizzes from the acid, it contains carbonate minerals, such as calcium carbonate, the main ingredient in limestone, marble, and coral. A more sophisticated approach involves an instrument called a mass spectrometer. It can determine the composition of tiny amounts of matter.
Geochemistry has many practical uses. For example, volcanic gas geochemists monitor the composition of gases at a volcano to determine if it is about to erupt. Aqueous geochemists study the chemical properties and changes in natural water sources to help ensure the water is safe for human consumption. Exploration geochemists help locate underground deposits of ore, natural gas, and petroleum by looking for chemical clues.
A branch of geochemistry called isotope geology involves measuring the isotopes of various elements. Scientists can determine the age of certain materials that are less than about 50,000 years old by measuring their amount of carbon 14, a radioactive form of carbon (see Radiocarbon (Radiocarbon dating) . Measurements of other elements, such as lead and strontium isotopes, reveal the age of much older material. Similar measurements in moon rocks and meteorites have contributed to our knowledge of the formation of the solar system.
Geochemists often consider elements that behave similarly or that are found together in nature to be part of a group. For example, rock-forming minerals that make up Earth’s crust (rocky outer shell) are considered a group. Most of these minerals consist of various metals chemically bonded to oxygen. Earth’s core consists primarily of the elements iron and nickel. The atmosphere contains mostly elemental nitrogen and oxygen. All other atmospheric gases, including the compounds carbon dioxide and water vapor, account for about 1 percent of the total.
