There are those who are proposing the once the canopy was removed, hence the flood from downpour, the oxygen then contained radiation ultraviolet light and other contaniments that reduced it and changed the world. One of the things they say changed is the growth factor of all on the planet. Let's say that we are 25%oxygen today and 35%n before the flood. The growth of plants would increaed greatly.. We all would in turn grown greatly and live longer. This might explain the difference in the world then and that of after the flood.