NASA has discovered a new life form, a bacteria called GFAJ-1 that is unlike anything currently living in planet Earth. It's capable of using arsenic to build its DNA, RNA, proteins, and cell membranes. This changes everything. Updated.
NASA is saying that this is "life as we do not know it". The reason is that all life on Earth is made of six components: Carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. Every being, from the smallest amoeba to the largest whale, share the same life stream. Our DNA blocks are all the same.
That was true until today. In a surprising revelation, NASA scientist Felisa Wolfe-Simon and her team have found a bacteria whose DNA is completely alien to what we know today, working differently than the rest of the organisms in the planet. Instead of using phosphorus, the newly discovered microorganism—called GFAJ-1 and found in Mono Lake, California—uses the poisonous arsenic for its building blocks. Arsenic is an element poisonous to every other living creature in the planet except for a few specialized microscopic creatures.
The new life forms up close, at five micrometers.
According to Wolfe-Simon, they knew that "some microbes can breathe arsenic, but what we've found is a microbe doing something new—building parts of itself out of arsenic." The implications of this discovery are enormous to our understanding of life itself and the possibility of finding organisms in other planets that don't have to be like planet Earth. Like NASA's Ed Weiler says: "The definition of life has just expanded."

Here's the organism and a computer simulation on how it substitutes phosphorus for arsenic in its DNA
Talking at the NASA conference, Wolfe-Simon said that the important thing in their study is that this breaks our ideas on how life can be created and grow, pointing out that scientists will now be looking for new types of organisms and metabolism that not only uses arsenic, but other elements as well. She says that she's working on a few possibilities herself.
NASA's geobiologist Pamela Conrad thinks that the discovery is huge and "phenomenal," comparing it to the Star Trek episode in which the Enterprise crew finds Horta, a silicon-based alien life form that can't be detected with tricorders because it wasn't carbon-based. It's like saying that we may be looking for new life in the wrong places with the wrong methods. Indeed, NASA tweeted that this discovery "will change how we search for life elsewhere in the Universe."
Mono Lake, California. Image by Sathish J — Creative Commons
I don't know about you but I've not been so excited about bacteria since my STD tests came back clean. And that's without counting yesterday's announcement on the discovery of a massive number of red dwarf stars, which may harbor a trillion Earths, dramatically increasing our chances of finding extraterrestrial life.