Molybdenum

Molybdenum (pronounced /məˈlɪbdənəm/, from the Greek word for the metal "lead"), is a Group 6 chemical element with the symbol Mo and atomic number 42. The free element, which is a silvery metal, has the sixth-highest melting point of any element. It readily forms hard, stable carbides, and for this reason it is often used in high-strength steel alloys. Molybdenum does not occur as the free metal in nature, but rather in a variety of oxidation states in minerals. Industrially molybdenum compounds are used in high-pressure and temperature resistant greases between metals, as pigments, and catalysts.

Molybdenum minerals have long been known, but the element was "discovered" (in the sense of differentiating it as a new entity from minerals salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm.

Most of molybdenum's compounds have poor water-solubility, but the molybdate ion MoO2−4 is soluble, and will form if molybdenum-containing minerals are in contact with free oxygen and water. Recent theories suggest that the release of free oxygen by early life was important in removing molybdenum from minerals into a soluble form in the early oceans, where it was available to be used as a catalyst by single-celled organisms. This sequence may have been important in the history of life, because molybdenum-containing enzymes then became the most important catalysts used by some bacteria to break the bond in atmospheric molecular nitrogen, allowing biological nitrogen fixation. This, in turn allowed biologically driven nitrogen-fertilization of the oceans, and thus the development of more complex organisms. Aside from bacterial enzymes involved with nitrogen fixation, about 20 different molybdenum-containing enzymes are known today in animals. Molybdenum is a required element for life in these higher organisms, though not in all bacteria.

From http://en.wikipedia.org/