If DNA-based life were ever found on Mars how would you definitively show that it was not polluted from earth?

What would the criteria for such a proof be?

What are the empirical demarcations that seperate pollution and panspermia?

(I'm assuming that the seperate and independent development of dna on mars and tellus is unlikely for now, although an emanation perspective would suggest otherwise)

Trob

Ps: hope its not a stupid question. :wink:

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second technician Rimmer, Arnold J., experienced what can only be described as a voyage to trip-out city

I don't know if there would be any definitive way of making such a differentiation. Presumably an analysis of the DNA would give a degree of resemblance to life on Earth at some stage. If it resembles modern bacteria, then odds are we're looking at pollution. If the genetic code is different or there are other dramatic variations, then that improves the likelihood of panspermia.

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Everything I need to know I learned through Googling.

s/improves/decreases/

If the genetic code is the same, then we can say with near certainty that life on Earth and Mars did not have independent abiogenesis. If the genetic code is different and not a minor variant then we can say with confidence that life of Earth and Mars does not have a common ancestor.

The reason why we can say this is simple: the number of possible genetic codes is astronomical. Especially since we not only can have
a different codon(s) code for a particular amino acid residue but
it is very possible that alien life would not use the exact same
set of amino acids as we do. And then, alien life might not even use amino acids, might the opposite enantiomers for either the DNA/RNA or the aminoacids, etc.

Is there any way that life could have been transferred from Earth to Mars within, say, the last billion years?

Edit: not counting transfers due to human activity, of course.

Toseek wrote:
Do you have any references for this - I would love to read it.

I was reasoning under the assumption that xeno- or exobiology mainly utilized anology, hence the search for extremophiles. Thus if life on earth and on mars had a common origin ( and therfore ultimately a common "core" dna) and were faced with the same ecological challenges a common strategy would result, and hence similar dna.
Indeed such a reasoning could be supported by the fact that the more extreme the enviroment, the less strageties are open for evolution. We know this from earth, because there is less variety in extreeme enviroments, whereas ideal enviromens result in a multitude of species (just think of the Rainforests of the Amazon as compared to the bacteria of the Mariana trench http://www.jamstec.go.jp/jamstec-e/bio/detal/MPR1.html )

My question is thus, if these bacteria had a similar strategy to those extremophiles of earth, and were dna based, rather than some other coding system - would this not result in a similar code?
Buf of course I might just be ignorant - hence my initial question.

All the best
Trob

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second technician Rimmer, Arnold J., experienced what can only be described as a voyage to trip-out city

Sure - if meteorites from Mars can land on Earth, then meteorites from Earth can land on Mars. The impact that ended the reign of the dinosaurs could easily have sent material upward at escape velocity.

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Everything I need to know I learned through Googling.

That's why the outer solar system is so tempting - it seems that the inner planets have been exchanging rocks for a quite a while - it may be hard to distinguish where life or the organic seeds of life came from - a sort of solar system wide paternity case!

However, the odds that Earth rocks made it to Titan are astronomically smaller than Mars, so anything found there will be most likely home grown, unless some ESA tech prepping Huygens for launch had a cold... 8-[

But, we really are in the infancy of astrobiology. We haven't even discovered and described all the environments on Earth that hold life, let alone our immediate neighborhood. It's going to get much more exciting in our life times!

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Lyford Rome
"Zis is not nuts, zis is super-nuts!"
Mathematician Richard Courant on viewing an Orion test