The Archaean eon has began roughly 4600 MYA. Before this time, there was no Earth, no planets, and no solar system - just a lot of dust swirling in space around the primitive Sun; in time, under gravity, this dust formed planets, which included the Earth. For first few hundred million years Earth was uninhabitable - bombarded by meteorites, poisonous gases and so. No life forms could exist on this planet. The Archaean eon ended 2500 MYA, when the Proterozoic eon had began.