We do not NEED another explanation, but there are quite a few good books which talk about the post flood and pre flood world and how the removal of the water vapor barrier at the highest altitudes allowed radiation to affect our genes and cause the degradation of what God created.
“The world that then was perished”
I read somewhere, that there was a higher level of oxygen before the flood that would have contributed to longer lifespans.
Excellent book discusses just that:
http://www.chick.com/catalog/books/1254.asp