Shiva Linga is composted of Terrestrial stone which is a good conductor of heat and electricity. Base is denoted as Yoni and Phallus is the “Linga”. Myth is that union of Terrestrial stone (Linga) and base (Yoni) is required for creation. The stone with this shape at the time of Vedic age was considered as phenomenon that often used for earthing devices that can save the village from thunderstorms. These thunderstorms are more often in rainy seasons after the summers, but high heat of summers could break a phallus linga and earthing current from the lightening of thunderstorm is not possible. People used to pour water on such stones so that Linga could’t be damaged.
How Linga then was associated with Shiva?
Linga Purana states that When Rudra (Lord of storms) got violent, Shiva assumed the form of Linga and Shakti becomes its base by assuming the form of Yoni. The process calmed down the storms. Shiva who is known as Mahadeva was/is an eternal being of the universe,who used to dwell on the Earth. During Vedic age, the aliens used to come to earth to have resources few of them found residence, Shiva was one of them. Shiva was having complete knowledge of time, physics and medical surgery. So he gave the knowledge of Linga -Yoni concept to 13 great sages, 12 ancient Lingas are known to us and 13th one is missing. 13th one is the last Linga was offered to Shukracharya i.e. another alien who was having accomplishment/powers of Venus.