If life off Earth is discovered, what evidence would science require to prove that the life does not share a common ancestor with life on Earth? In other words, how could science prove that this newly discovered life resulted from a different "genesis" than life on Earth?

A different genetic code?  A non-carbon molecular base? A different DNA structure?

Thanks for your thoughts!

2 hours ago, john.calixte said:

If life off Earth is discovered, what evidence would science require to prove that the life does not share a common ancestor with life on Earth? In other words, how could science prove that this newly discovered life resulted from a different "genesis" than life on Earth?

A different genetic code?  A non-carbon molecular base? A different DNA structure?

Thanks for your thoughts!

It would depend on how similar the life found off earth was to life on earth... If for instance life was found on Titan it would be so different from earth life it would have to be a second genesis of life. 

13 hours ago, john.calixte said:

A different genetic code?  A non-carbon molecular base? A different DNA structure?

It's an interesting question.

Is some form of genetic material (something encodes information about the physical structure) essential to life? Perhaps only if that lifeforms is going to evolve. We can imagine some sort of cellular organisms that reproduces by growing and splitting so it doesn't need anything to encode a genotype separate from the phenotype.

If it does have some sort of genetic material, would it need to be DNA? It is quite possible that there are other molecular structures that could be used to encode information.

If there was DNA, would it use the same encoding to create the same amino acids? It could use different bases and synthesise different products.

If it were the same DNA and encoded the same proteins, then there could a be a good argument for a shared origin. But it could be an example of convergent [chemcial] evolution. But maybe DNA encoding those proteins is the only mechanism that works. Until we find some examples, we just won't know!

13 hours ago, john.calixte said:

A non-carbon molecular base?

That seems unlikely. There aren't really other elements that support such a wide range of structures. But it might be that very simple structures could be formed, based on sulphur or something, that were able to meet some definition of "living".

1 hour ago, Strange said:

It's an interesting question.

Is some form of genetic material (something encodes information about the physical structure) essential to life? Perhaps only if that lifeforms is going to evolve. We can imagine some sort of cellular organisms that reproduces by growing and splitting so it doesn't need anything to encode a genotype separate from the phenotype.

If it does have some sort of genetic material, would it need to be DNA? It is quite possible that there are other molecular structures that could be used to encode information.

Other bases are being used in artificial life forms, the scientists call it XNA. 

1 hour ago, Strange said:

If there was DNA, would it use the same encoding to create the same amino acids? It could use different bases and synthesise different products.

If it were the same DNA and encoded the same proteins, then there could a be a good argument for a shared origin. But it could be an example of convergent [chemcial] evolution. But maybe DNA encoding those proteins is the only mechanism that works. Until we find some examples, we just won't know!

That seems unlikely. There aren't really other elements that support such a wide range of structures. But it might be that very simple structures could be formed, based on sulphur or something, that were able to meet some definition of "living".

Silicon might work under very cold conditions, Silicone might work in very hot conditions, maybe with sulfuric acid as a working fluid, I'm betting any life will be based on carbon or maybe and I mean a very small maybe, Boron. 

9 hours ago, Strange said:

If it were the same DNA and encoded the same proteins, then there could a be a good argument for a shared origin. But it could be an example of convergent [chemcial] evolution.

Interesting!  Convergent evolution of the genetic code from different origins. The answer to my question could get complicated.