أنت تسأل وDarwin يجيب .

SILICON is the most abundant element on earth, but is not found free in nature. It occurs either as the oxide silica in sand and quartz or as silicates in such materials as granite. It is also found in the ashes of plants and in the human skeleton. Indicating its hardness, silicon was named from the Latin silex or silicis, meaning "flint."

Early chemists considered "silica" an elementary substance. By 1787, it was suspected that the substance was an oxide of an undiscovered element. This theory was expanded upon by a Swedish chemist in 1823, but not until 1972 was it declared an essential element for normal growth and skeletal development of lab animals. The body contains about 18 grams of the substance throughout structured tissue, mainly in the aorta, bone, tendons, and skin.

It is believed to function in the metabolism of connective tissue, the formation of collagen, the calcification of bone, and the maintenance of elastic tissue integrity. Many naturopaths feel that silicon and calcium are closely related in the body's metabolism, since weaknesses in bone and connective tissue (collagen) are partially related to the silicon status. A deficiency results in growth retardation and incomplete development of the skeleton. There is also evidence of an inverse relationship between the silicon content of the arterial wall and the degree of atherosclerosis present, and may also be involved in osteoarthritis, HTN, and the aging process.

Silicon is supplied in unrefined foods, especially grains, cereal products, and root vegetables, but food products of animal origin are poor sources. Silicates are sometimes used as food additives. There is no known minimum requirement for humans. No toxicities are known, since it is so poorly absorbed from food, with practically all of it being excreted.

Names include: Si, and element 14.
Deficiency symptoms include: slow healing, angina, fatigue, dull/glazed eyes, decreased growth, skin pallor, deterioration of memory, tooth demineralization, abnormal tooth enamel, deformed bones and deterioration of bone growth, distorted eye socket development, deterioration of collagen formation, skin flabbiness, decreased skin elasticity, carbuncles, hair falling out, ribbed nails, ingrown nails, deterioration of embryonic development, and decreased immunity.
Helpers include: Vitamin C and calcium

Where did life originate and how?
Extra-terrestrial: In 1969, a meteorite (left-over bits from the origin of the solar system) landed near Allende, Mexico. The Allende Meteorite (and others of its sort) have been analyzed and found to contain amino acids, the building blocks of proteins, one of the four organic molecule groups basic to all life. The idea of panspermia hypothesized that life originated out in space and came to earth inside a meteorite. Recently, this idea has been revived as Cosmic Ancestry. The amino acids recovered from meteorites are in a group known as exotics: they do not occur in the chemical systems of living things. The ET theory is now not considered by most scientists to be correct, although the August 1996 discovery of the Martian meteorite and its possible fossils have revived thought of life elsewhere in the Solar System.