D'où vient cette eau immense, accumulée, qui s'appelle mer ? On connaît la barrière (barzakh) originellement posée par Dieu entre les deux masses aquatiques douce et salée et aussi, sous un autre éclairage, le sel que l'eau rebelle reçut pour prix de sa révolte, lorsqu'elle tarda à regagner ses repaires premiers après le Déluge. L'origine cosmogonique est reprise, avec d'autres explications relevant de la physique, par Mas'ûdî :

In Arab geographic literature from around the year 1000, the sea is much less well-known than the land. Historical thought concerning the phenomenon of the sea, nourished by the traditions of Aristotelianism and of the Qur'an intersected with the inadequacies of a body of knowledge which was content to perceive the sea only from its shores. The only seas which were truly described in this literature are those whose shores belong to the Muslim world ; the Southern Mediterranean, the Western portions of the Indian Ocean with its extensions to Iraq and Suez, and the Caspian. As a whole, the sea was viewed as a mysterious world, one with its own laws, landscapes and beings: a world which should be tamed rather than loved in order to extract its nourishment and its riches, such as amber, pearls and coral. It was a world which, much more than the land, was the privileged refuge of Satan.