Calcium strontium or barium, the oxide–nitride coating that results in air is stable and lathe machining and other standard metallurgical techniques are suitable for calcium. In the United States and Canada, calcium is instead produced by reducing lime with aluminium at high temperatures. Calcium provides a link between tectonics, climate, and the carbon cycle. In the simplest terms, uplift of mountains exposes calcium-bearing rocks to chemical weathering and releases Ca into surface water. These ions are transported to the ocean where they react with dissolved CO to form limestone (), which in turn settles to the sea floor where it is
Gender symbol two standard sex symbols are the Mars symbol ♂ (often considered to represent a shield and spear) for male and Venus symbol ♀ (often considered to represent a bronze mirror with a handle) for female, derived from astrological symbols, denoting the classical planets Mars and Venus, respectively. They were first used to denote the effective sex of plants (i.e. sex of individual in a given crossbreed, since most plants are hermaphroditic) by Carl Linnaeus in 1751. They are still used in scientific publications to indicate the sex of an individual, for example of a patient. Pedigree charts published in scientific