Lord Vishnu took his third incarnation as a boar. In this incarnation Lord Vishnu rescued the earth which had submerged in the ocean, and brought it out from the ocean. The whole creation started only after that. A demon by the name of Hiranyaksha had abducted the earth and carried it to the Rasatala (the second lowest of the world). The earth is considered to be as a Woman and since it is a crime to abduct a woman therefore Lord Vishnu in his incarnation of a boar killed the demon Hiranyaksha and liberated the earth from his clutches.