Elements found in the human body. The most abundant elements in the body (red), lesser elements (blue), and trace elements (green). Source: Dept. of Chemistry, University of Florida.
A trace element is any of a number of elements required by living organisms, in small amounts, to ensure normal growth, development, and maintenance. They do not include the basic elements of organic compounds (carbon, hydrogen, oxygen, and nitrogen) or the other major elements present in quantities greater than about 0.005% (calcium, phosphorus, potassium, sodium, chlorine, sulfur, and magnesium). See essential element.
Trace elements found in the human body are iron, manganese, zinc, copper, iodine, cobalt, molybdenum, selenium, chromium, silicon, fluorine, vanadium, nickel, arsenic, and tin. See also elements, biological abundance.
Because living things serve to locally concentrate trace elements, accumulations of these elements in rocks serve as biomarkers which astrobiologists will be able to use in their search for extraterrestrial life.