In Ancient Hindu cosmology, the world is divided into seven concentric continents: Jambudvipa, Plaksadvipa, Salmalidvipa, Kusadvipa, Krouncadvipa, Sakadvipa, and Pushkaradvipa. These continents are separated by seven seas: the first sea is filled with salt water, second with sugarcane juice, third with wine, fourth with ghee, fifth with curd, sixth with milk, and the seventh with water. The last sea, in the outer periphery, is surrounded by the mountain range called Lokaloka (world and no-world) which is ten thousand yoganas (one yogana is 12 to 15 kilometers) in breadth and as many in height—it forms the boundary between the knowable world and the dark void of nothingness.
Hinduism was founded in Jambudvipa, the innermost of the seven continents. Jambudvipa is also known as Sudarshanadvipa. In Markandeya Purana, Jambudvipa is described as a sublime land that is depressed in the southern and northern regions, and in its middle there is an elevated and broad land called Ila-vrta or Meruvarsha. In the center of Meruvarsha, there is the golden mountain called Mount Meru, on whose summit there is a vast city called Brahmapuri, the abode of the God of Creation, Brahma. Around Brahmapuri, there are eight cities, each presided by its own God, one of these Gods is Indra, the King of heaven and all Gods.
In another visualization given in the Markandeya Purana, Jambudvipa is divided into four regions, which are shaped like the four petals of a lotus. Mount Meru rises from the center, and the city of Brahmapuri is surrounded by the river Akash Ganga, which flows from the foot of Vishnu. Akash Ganga meanders through the lunar regions, before descending from the sky. After encircling Brahmapuri, it divides into four streams which irrigate the entire continent of Jambudvipa.
How old is the Hindu cosmology of seven continents and seven seas? It is impossible to date the Markandeya Purana and the other Puranas. Most scholars believe that the Markandeya Purana (which is probably the oldest Purana) was developed in the seventh century BC. But the Puranas could belong to prehistory, which in Indian context means during or before the Harappan era (5500—1900 BC). The Harappan era did not begin in a vacuum—Agriculture and settled life began in South Asia around 7000 BC. The cosmological theories in the Puranas could be rooted in cultures that are much older than the Harappan civilization.