Lifespans in Genesis & a Timeline

While reading about Abraham recently, I started thinking "where did all these people come from?" Not only does Abraham keep running into new people, but cities have also been founded.

Turns out Abraham is born 1,948 years after creation, judging purely on the accounts of lifespans. It's interesting how large that distance is, especially when they feel so connected and close in Genesis.

Full link & timeline here.

What do you think? Is it fair to do things like this? Are the lifespans meant to be taken literally? And -- of course -- what enabled them to live so long? Are the years solar years?

If you want to see an interesting discussion on Google Answers (I don't know if I endorse any particular opinion), check this out. Spoiler alerts though -- maybe you want to form your own opinion first?

For future reference:
Timeline URL: http://www.practicalchristianliving.org/timeline.htm
Google discussion on lifespans: http://answers.google.com/answers/threadview/id/538112.html