 The initial chapters of the third book of the "Vishnu Purana" presents its theory of "manvantaras", or Manus-ages (each equals about 4.3 million years).This is premised upon the Hindu belief that everything is cyclic, and even "Yuga" (era, ages) start, mature and then dissolve.Six manvantaras, states the text, have already passed, and the current age belong to the seventh.