Coal is formed when peat is altered physically and chemically. This process is called coalification.. During coalification, peat undergoes several changes as a result of bacterial decay, compaction, heat, and time.
On January 9, 2011, ABC Family announced the show would return for its fourth season on March 26, 2011. On February 2, 2012, ABC Family renewed the series for a fifth season. On October 9, 2012, it was announced that the fifth season of The Secret Life of the American Teenager would be the final season. The series finale aired on June 3, 2013.
It started in 1963 with the story An Unearthly Child. Up to the point it was cancelled in 1989 there were 26 seasons (26 years) and 155 individual stories (stories were generally made up of 4 episodes).