I just found this article:

http://www.nytimes.com/2010/05/14/opini ... ef=opinion

Could our resident biologist tell us if Mr. Davies' hypothesis is viable? If so, it would open all kinds of interesting avenues for ET life as well...

Cheers,

Eloise

Funny you should bring this up today, Eloise! I'm writing an article about Davies' book The Eerie Silence, which will touch upon his biological theories.

There is no question that there may be lifeforms that we haven't seen or that we cannot easily recognize. However, some of the "second life" ideas have serious problems.

Arsenic is to phosphorous what silicon is to carbon: namely, a vastly inferior cousin. Each pair is in the same column of the periodic table, which means that they share some properties but the "lighter" member of each pair, phosphorus and carbon, respectively, are much better at reactions.

Lifeforms of different handedness would have to find such molecules for structure and food. This is a very tall order, to put it mildly -- and we haven't found such biomolecules anywhere we've looked on Earth.

Of course, all bets are off the moment we step off Earth!