no, its not because of sin, in the book of genesis god divided the waters into 2 firmaments. one upper and one lower. This created a water canopy over the earth. now, with this water canopy, it blocked all ultra violant radiation and increased oxygen in the enviorment to 3 times the ammount we see today. This is scientificly proven. As you see in the Bible, people live shorter and shorter lives as time goes by. But this dosent happen untill after Noah. When God flooded the world he dropped the upper firmament onto the earth and opened up all the springs on the earth. with the upper firmament gone, this changed the long life people used to live and how big things got. Have you noticed that things from back then were alot bigger than now. bigger mosquitos, bugs, birds, fish etc. everything was much bigger growing in that Oxygen rich enviorment. This has been tested with fish in a lab whear they made the same conditions. They grew Parranas to be 7 times larger than a normal parrana. It is fasinating that creation science can prove the neatest things and the beauty of Gods creation. I hope this helps:fish:
Nope.it never rained til the flood, did it?