Its name is derived from the Greek words Ï Î Î Î 1\/2 Ï and Î Ï Î , meaning make life appear , since it was once believed that life began in the Cambrian , the first geological period of this eon . Its name derives from the Greek words Ï Î Î 1\/2 Î Ï Ï Ï and Î Ï Î , meaning visible life , since it was once believed that life began in the Cambrian , the first period of this eon .