Thales of Miletus, who has made detailed observations on triangulation navigation methods, dies holding the belief that the Earth floats on water; that all things come to be from water; and that all things somehow consist of water.

Thales’ pupil and successor Anaximander of Miletus, who wrote a comprehensive history of the universe that hypothesizes nonmythological explanations for the creation, dies only a year after his teacher.

Challenging Thales' position that a single element can be the origin of all, Anaximander argued that, because known elements are constantly opposing and changing into one another, something different from these elements must therefore underlie and cause changes, postulating the “apeiron” ("boundless," or "indefinite") as the originative and sustaining substance.

Anaximander, believing Earth to be cylindrically shaped, drew the first known world map; he also speculated about the origins of marine life.

Greek philosopher Anaximenes, the last of the Milesian school founded by Thales, maintains that the primary substance is air (Greek, “aer”); everything else in the world, including the gods, is no more than condensed or rarefied air: condensation transforms air into wind, water and earth; rarefaction heats air and transforms it into fire, in this way explaining the sun and other celestial bodies.