Silicon based life forms. Artwork of an alien landscape with life forms composed of silicon. Silicon is close to the element carbon in the periodic table. It has similar chemical properties to carbon being able to bond with other elements such as hydrogen and oxygen to form complex molecules. Some theories suggest that alien life forms could exist based on silicon chemistry. Such creatures, seen here left, centre and right of image, would look crystalline in appearance and withstand high temperatures due to the heat stability of silicon compounds.