The beginning of the Book of Genesis has been seen as describing the state before a climate change in a certain region. >Because of this change, humans were "condemned" to growing crops and keeping some food in stock, to be able to eat it, during the times it did not grow. Genesis has been seen to only start when this region converted to agriculture (the Neolithic Revolution, mentioned above). This means that Genesis roughly covers the time from about 8000 - 6000 BC to about 2000 BC.