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During their travels ancient Greeks could come in contact with other tribes and their ideas. What they learned was used in order to they produce a first cosmology. The seamen could direct themselves by noticing celestial bodies and their orbits. The periodicities that they observed helped them learn something more important: These periodicities did not result from Gods, but from certain natural laws.
Proportional conclusions came out from the succession of seasons. Of course, one realises that this was not an easy process neither direct. 
It took them centuries, but the result was magnificent. This is the point where what we call science emerges. As a result, mythology began little by little to be brought down and it was finally replaced by an opinion for the universe based in intellect. Anaxagoras from the Klazomenes considered first that the light of the moon. He also used to believe that the sun was a piece of melted iron, much bigger than Peloponnesus.
Thales from the Militos, at 585 b.C. forecasted an eclipse of the sun, by studying Babylonians' work. At this period there were proposed other ideas, e.g. that of the eternal universe from the Democritus. Another sample of logic came from Anaxagoras, who considered that the meteorites, that appeared to fall from the sky, were emanated from the Earth. These pieces had been extracted by the Earth because of its very fast rotation, but away from the Earth had to fall once again on it. In a while all these endeavours finally could answer all the questions about the universe.
Anaxjmenes from the Militos proposed four elements, from which resulted everything. These were the Earth, the air, the water and the fire. This concept was not accepted at once, but it was a really good starting.
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