Re:There Probably Have Been Aliens
by marcosdumay on Monday January 23, 2017 @04:50PM
(#13466402)
I'm not following the reasoning about a lower bound. I didn't use the size of the universe anywhere.
> However, life showed up on earth at a very early stage which suggest it has a relatively high probability over a planets lifespan.
1 - That's a good explanation. As good as any other.
2 - Alternatively, life's appearance depends on something that only existed in that short timespan (both light and a big temperature gradient at the same place is a great candidate).
3 - Or life requires some time to evolve so intelligence can only appear on planets that life was early.
4 - Or, you can mix #2 and #3 at varying amounts.
However, life showed up on earth at a very early stage which suggest it has a relatively high probability over a planets lifespan. Without other information to go on earth is probably topical and life generally shows up within the first 500 million years watter shows up.