[elnate]

In regards to the contamination,

I don't think that would be a real risk. Earth life has spent billions of years both adapting and adapting to the environment to make it the best growing medium and even then it exists in exclusive bands. For example, put a polar bear in the desert or a fresh water fish in salt water. It is more likely that we would have to take extreme care not to kill any lifeforms we brought back than to worry about them killing us.

[jmpe]

You're seriously underestimating this issue.

- rabbits/cane toads in Australia [0][1]

- Japanese knotweed [2]

- Tumbleweed (yep, not as native as Hollywood suggests) [3]

- Algae [4]

... and the list goes on and on, here's a top-100:

http://en.wikipedia.org/wiki/List_of_the_world%27s_100_worst...

[0] http://www.youtube.com/watch?v=pgPhn4tYxJQ

[1] http://en.wikipedia.org/wiki/Cane_toads_in_Australia

[2] http://www.environment-agency.gov.uk/homeandleisure/wildlife...

[3] http://en.wikipedia.org/wiki/Kali_tragus

[4] http://plants.ifas.ufl.edu/node/89

[TeMPOraL]

I don't think anyone is worried about space bears or space fish; but bacteria / viruses / other basic replicator forms have much bigger resistance to harsh environments.