So, life on Mars...

[trappedslider]

View attachment 416763

 

[Umbran]

The way our DNA makes base pairs is not particularly special.

?
DNA doesn't make base pairs. It is made of base pairs.

It would be astoundingly unlikely that two independently evolved forms of life would have the same base pair system.

So, now we get fiddly...

Independently developing DNA to encode information would not be strange, because it has the right general characteristics, and tends to form self-organized states even when there is no life present.

What is likely to be different is the encoding. On Earth we generally use groupings of three nucleotide bases (called a codon) to code for one type of amino acid.

But, you have DNA in the nuclei of your cells, and in your mitochondria. And they use different codons! On Earth, there are no fewer than 37 different encoding schemes all using DNA. Of course DNA from another planet would use different encoding.

 

[Clint_L]

"Extraordinary claims require extraordinary evidence" (Carl Sagan). This seems more on the order of "promising evidence." So...not a bombshell. I remain hopeful.

 

[Reynard]

?
DNA doesn't make base pairs. It is made of base pairs.



So, now we get fiddly...

Independently developing DNA to encode information would not be strange, because it has the right general characteristics, and tends to form self-organized states even when there is no life present.

What is likely to be different is the encoding. On Earth we generally use groupings of three nucleotide bases (called a codon) to code for one type of amino acid.

But, you have DNA in the nuclei of your cells, and in your mitochondria. And they use different codons! On Earth, there are no fewer than 37 different encoding schemes all using DNA. Of course DNA from another planet would use different encoding.

We have discovered that there are over a million potential nucleic acids. The way our biology worked out was a fluke. It would be very strange if another system looked like ours.

 

[Umbran]

We have discovered that there are over a million potential nucleic acids. The way our biology worked out was a fluke. It would be very strange if another system looked like ours.

Again you seem to be confusing system and material. I already noted that the system would be different.

Saying "DNA" is like saying "protein" or "carbohydrate". It doesn't give you specifics of structure or operation.

 

[The Firebird]

Again you seem to be confusing system and material. I already noted that the system would be different.

Saying "DNA" is like saying "protein" or "carbohydrate". It doesn't give you specifics of structure or operation.

The original post said "same DNA". I read that to mean same base pairs, the same way "the same proteins as earth" means both "L-amino acids" and "the same 20 amino acids as earth".

 

[Reynard]

Again you seem to be confusing system and material. I already noted that the system would be different.

Saying "DNA" is like saying "protein" or "carbohydrate". It doesn't give you specifics of structure or operation.

Okay. But my point is that the probability that two independently evolved DNA systems would look similar is vanishingly small, thus my assertion that finding such would strongly suggest a common cause or ancestor.

 

[The Firebird]

Okay. But my point is that the probability that two independently evolved DNA systems would look similar is vanishingly small, thus my assertion that finding such would strongly suggest a common cause or ancestor.

The common cause idea is super interesting to me. We don't know very much about origin of life chemistry and based on what environment it is in different choices could be more likely. Guanine, for example is very abundant (relatively) in meteorite extracts but hard to synthesize in the lab. To what extent is the choice constrained by the local chemistry? The local chemistry which is good for life may favor a small set of nucleobases only.

That said, at last count I saw maybe 30 different bases had been found in meteorites, noting that does not say anything about DNA, or more properly RNA formation.

 

[Umbran]

Okay. But my point is that the probability that two independently evolved DNA systems would look similar is vanishingly small, thus my assertion that finding such would strongly suggest a common cause or ancestor.

And I am saying, "define similar".

Like, there being potentially over a million different nucleic acids doesn't actually mean anything, if only around 20 easily come about through abiogenic means.

Similarity is suggestive of shared ancestry only in the absence of other explanations for the similarity.

 

[Umbran]

The common cause idea is super interesting to me.

It is... and it isn't.

We've identified at least 60 meteorites on Earth that probably originated on Mars.

Stuff gets around. Life finds a way.