It may just be that our particular phosphate-based DNA is not the only game in town - or out of town.

 

http://www.bbc.co.uk/news/science-environment-11886943

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Absolutely, check out the NASA press conference which starts in 10 minutes!

http://www.nasa.gov/multimedia/nasatv/index.html?param=public
I watched the press conference. The lead researcher was a bit silly but competent. I guess she was just very happy and excited. Can't blame her.
A senior scientist for NASA's program in astrobiology: "These bugs haven't just replaced one useful element with another, they have the arsenic in the basic building blocks of their makeup, We don't know if the arsenic replaced phosphorus or if it was there from the very beginning - in which case it would strongly suggest the existence of a shadow biosphere."
HAHAHAHA! Yup, that's about what happened at my school when we watched it. Rofl. I am getting my PhD in microbial ecology so this news is a big deal; for all biology really.

On a more serious note, I think it's a fascinating possibility. I was able to read the Science paper and decided that the evidence so far is good, but not unequivocal. They have several more simple experiments they could have done for it to be really amazing. Hopefully they will do them and this will be a biological sensation. Until then I am enthusiastic but cautious.
The arsenate seems to be a poor substitute for phosphate. While the cell can use it to fill a need, kinda like Haitians eating mud cookies, would evolution proceed to RNA and DNA with only arsenic available?
No idea :( Doesn't seem likely, though. I don't think it's a new evolutionary tree, to me it's a microbe that incorporates the next best thing to Phosphorus because they forced it to have only Arsenic. I have the Science paper if I knew how to share PDF's on here I would share it.
Link
http://www.sciencemag.org/content/early/2010/12/01/science.1197258

I thought that chemist explained it very well with the links he made and aluminum for the arsenic. He also made a good point that maybe in an environment which was VERY cold, a more reactive compound like arsenic could actually help the chemical reaction proceed. But then wouldn't all the molecules need to be more reactive? And in the universe, I am pretty sure P is more common than As, so it seems unnecessary to use As...
One simple experiment they could have done is to use enzyme assays- use an enzyme which modifies normal DNA and see if it works on the arsenic DNA. Cells need DNA polymerase to replicate DNA (so they can divide), so that would have been a good enzyme to test.
I agree. This leap to a shadow biota seems a bit of a stretch. I think our seeing the common and efficient chemistry of us as the most likely kind isn't just chauvinism, it's probably the stuff of most of the critters in the universe.

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