Magnesium was isolated by Humphry Davy in 1808, another product of his electrochemical campaign on the alkaline earths. Its name traces to Magnesia, a district of Thessaly in ancient Greece whose mineral wealth also lent its name to manganese and, through the lodestone, to the magnet. Two magnesia earths were distinguished by early chemists: magnesia alba, the white magnesium carbonate, and magnesia nigra, a black manganese ore. Magnesium is a light, silvery metal that burns with a brilliant white flame. The lightest of the common structural metals, it is used in aircraft and vehicle alloys and in flares and fireworks, while magnesium is also the atom at the centre of the chlorophyll molecule, making it indispensable to photosynthesis and thus to almost all life on Earth.
Because it burns so fiercely, hot enough to ignite underwater and too bright to look at directly, magnesium was adopted for military incendiary devices and flares in both World Wars, a stark counterpart to its gentler role lighting early photographic flashbulbs. In the body magnesium is the essential partner of ATP, the molecule that carries chemical energy in every living cell, so that the same element driving photosynthesis in plants is simultaneously required for hundreds of enzyme reactions in animals, making it one of a handful of elements indispensable on both sides of the food chain.