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Iridium

Iridium is one of the rarest elements on Earth. Therefore, when high levels of this element were discovered in several regions of the world, including the coast of Mexico, geologists believed that it was evidence of the cause of the extinction of the dinosaurs at the end of Cretaceous period. Located at all the boundaries between the Cretaceous and Tertiary geological periods is a thin layer containing iridium. This element is common in asteroids and comets, and it is believed that a high impact meteorite hit Earth, eliminating the dinosaurs.

Iridium was named for the Latin "iris," meaning rainbow, because its salts are distinctly coloured. This hard, brittle metal is highly resistant to corrosion.

Iridium is found in association with platinum and is also used in the production of hard platinum alloys that are heat resistant. Combinations of iridium and platinum are used in electrical contacts, such as electric spark plugs. A platinum-iridium alloy was once used to make the standard metre bar. Today the National Research Council Canada (NRC) maintains the standard length in Canada. The NRC now uses the spectral line from a helium-neon laser controlled to fall on an absorption line in a molecule of iodine to determine the standard of length.