Has NASA Discovered Evidence for Extraterresterial Life?

bcrowell

Arsenic-based life tastes like chicken, but I hear it's not good for you.

Ivan Seeking

Perhaps?

http://www.timesonline.co.uk/tol/new...cle7040864.ece

DaveC426913

Question about this arsenic thing. It's a substitute for phosphorus, right? But it's not a substitute for COHN-, or even RNA/DNA-based life, right?

This hypothetical arsenic-based life is still organic and based on RNA?

Yah, found this on Wiki:

Ygggdrasil

The hypothetical arsenic-"based" life would still be based primarily on carbon, oxygen, hydrogen and nitrogen. The main difference would be, as said in wikipedia, substitution of arsenic for phosphorus. Felisa Wolfe-Simon and co-authors argue that it is possible that such molecules could exist (without being too unstable to allow life) and why these types of molecules may have been easier for life to use on the early earth in an article in the International Journal of Astrobiology (abstract below):

"All known life requires phosphorus (P) in the form of inorganic phosphate (PO₄^3- or P_i) and phosphate-containing organic molecules. P_i serves as the backbone of the nucleic acids that constitute genetic material and as the major repository of chemical energy for metabolism in polyphosphate bonds. Arsenic (As) lies directly below P on the periodic table and so the two elements share many chemical properties, although their chemistries are sufficiently dissimilar that As cannot directly replace P in modern biochemistry. Arsenic is toxic because As and P are similar enough that organisms attempt this substitution. We hypothesize that ancient biochemical systems, analogous to but distinct from those known today, could have utilized arsenate in the equivalent biological role as phosphate. Organisms utilizing such 'weird life' biochemical pathways may have supported a 'shadow biosphere' at the time of the origin and early evolution of life on Earth or on other planets. Such organisms may even persist on Earth today, undetected, in unusual niches"

(Wolfe-Simon, Davies and Anbar. Did nature also choose arsenic? Int. J. Astrobiol 8: 69 (2009). doi:10.1017/S1473550408004394, article available on author's website)

In particular see fig 2 for the authors' speculative picture of As-RNA and As-DNA.

I would be absolutely stunned if Thursday's Science paper announced they found As-DNA or As-RNA. I could definitely see other aspects of arsenic metabolism (e.g. using it as an electron donor for the fixation of carbon dioxide) and maybe limited incorporation into some biosynthetic pathways, but an organisms with a form of genetic material chemically distinct from all other known organisms would be a huge discovery.

bobze

Well I know a lot of people are let down, but I'm pretty excited. Because this has major implications for the origins of life on earth. Arsenic compounds for things like nucleotides form much more readily than phosphorous ones. It may mean that nucleoside arsenates came before nucleoside phosphates.

Pretty cool.

Jack21222

Are you stunned?

It still uses some phosphorus, so it hasn't swapped ALL of it out for arsenic, but still, it's pretty freaking cool.

DaveC426913

Wow. I went to that page and the video completely froze my system - even the mouse (yet the audio played on). I had to do a hard boot recovery.

nismaratwork

Ouch, that's almost as bad as the early speculation on the news networks as to what this announcement was going to be.

Ygggdrasil

I was very stunned, then I read the paper, thought about it, and am skeptical of the claim that the bacteria uses As-DNA as its genetic material (it may contain As-DNA, but these would likely be nonfunctional). For my (very longwinded) thoughts on the paper, see my post on the biology board (http://www.physicsforums.com/showthr...06#post3016806).

Despite my skepticism, I still think the paper is very neat and exciting. Who knows what other undiscovered biochemistires are out these in other extreme environments.

_Tully

A cool discovery (creation?), but I think the hype is overshadowing the fact that we know water can support life without the need of atmosphere or sunlight, we've known this for a long time (I believe ever since we started poking around hydrothermal vents?). Isn't that a bit more exciting, or at least equally so, as we know there is plenty of water elsewhere?

Or has the excitement shifted from the astrobiological implications to biology in general? In which case, yes, very interesting!

Redbelly98

I am puzzled as to why NASA has any role in this. It is terrestrial biology.

FlexGunship

According to a new paper published in the journal Science, reporters are unable to thrive in an arsenic-rich environment.

FlexGunship

They funded the research under a branch of exobiology. Basically trying to answer the question: "what else should we look for that might indicate life?"

Orion1

Quote by CNN Washington (CNN) -- Scientists have discovered a form of bacteria that can thrive on arsenic -- an element generally considered toxic -- dramatically expanding both traditional notions of how life is sustained and the range of where it might be found in the universe, NASA funded-researchers said Thursday. The bacterium -- strain GFAJ-1 of the Halomonadaceae family of Gammaproteobacteria -- was scooped from sediment in California's Mono Lake, an area rife with high levels of naturally occurring arsenic, it said. Scientists were able to grow the microbes from the lake with only small portions of phosphorous -- considered an essential nutrient in the biomolecules of naturally occurring bacteria. The bacterium not only grew but also incorporated the arsenic molecules into its DNA (As-DNA), in place of phosphorus, she said.

According to my understand of molecular biology, an organism based upon As-DNA - if that is the proper scientific nomenclature for such a molecule, represents a new class of life that is relatively distinct from P-DNA. Similarly, a new class of life would also be represented by Si-DNA or Silicon based life where Silicon is replaced by Carbon, however such a class of life would have to respire Silicon Dioxide instead of Carbon Dioxide, and because Silicon Dioxide is not a gas, such a class of life is highly improbable.

With further genetic engineering of this bacterium away from P-DNA evolution, it may be possible for the organism to completely substitute Arsenic as As-DNA.

Applications for such a bacterium could involve removing Arsenic from contaminated soils and water.

Is the probability of class As-Si-DNA based life in the Universe non-zero?

Reference:
CNN - As-DNA

DaveC426913

Ivan Semaniuk made a good point in a sound bite.

He suggested it is not so much that this bacterium is making As-DNA, simply that As is getting substituted for P in the existing DNA.

Kind of like hemoglobin taking up CO instead of O, only more permanent (probably better examples of substitutions out there).

Ygggdrasil

Isaac Asimov, who has a PhD in biochemistry in addition to being a science fiction writer, discussed the conditions for alternative biochemistries in his essay "Not as we know it." Although he doesn't discuss arsenic-based life, he does discuss possible conditions for silicon-based life:

http://www.bigear.org/CSMO/HTML/CS09/cs09p05.htm

Ygggdrasil

Definitely not, especially because Si-life would not be expected to function at the temperatures and pressures present on Earth. Furthermore, it's still not clear whether the organism actually functions using As-DNA instead of P-DNA. The NASA study has implications only on the possibility of replacing phosphorus with arsenic, and does not provide any support for or against the existence of other such element substitutions.