Would we be able to tell if fossilized life on Mars is DNA-based?

[bostonnew]

Hi all,

If we find some fossils there, will we be able to tell if it's DNA-based? Similarly if we find fossils (or even current life) on Europa what is it likely to be based on?

I'm very curious if extraterrestrial life is like what we have here on earth or not.

It seems clear that whatever life we find we will be related to it in some way. But I would like to find some theories on how long we have to go back to find a "common ancestor". Will it be a supernova explosion that spread the chemical elements throughout our region of space, and then life evolved based on different elements? Or has life evolved in similar ways but independently on different planets. (like for example the evolution of the eye on earth)?

I realize we don't have answers to all these questions (and that I'm probably not phrasing the questions in the normal scientific way), but I would like to know what the leading researchers think.

Do you guys know where I can read more about these things?

[Ryan_m_b]

We wouldn't be able to tell if fossilized life on Mars or elsewhere, DNA doesn't fossilise and wont last long. Techniques for analysing ancient DNA (http://en.wikipedia.org/wiki/Ancient_DNA) are limited to around 1 million years.

Even if the original abiogenic chemicals arrived on Earth due to panspermia and also facilitated the formation of life elsewhere this would not count as a common ancestor as they only exist once life has begun. We don't yet have a comprehensive theory of abiogenesis (http://en.wikipedia.org/wiki/Abiogenesis) so we can't really say for certain how life started. There is a lot of speculation and study on how life could form elsewhere, this field is called astrobiology (http://en.wikipedia.org/wiki/Astrobiology).

[bostonnew]

Ok, thanks.

How about just by looking at the shape and other aspects of the fossil? Would that tell us anything about how we're related to it?

[LeroyLaRey]

If it's identifiable at all, it will have something in common with earth organisms. If the shape is identifiable (like cilia or vacuoles), similar organs on earth (governed by dna) could imply similar dna influence there too. But I expect that because gravity and chemistry is different, the forms will have developed differently. We can calculate how long ago the organ in question developed on earth to give a time frame for contact (but it could be either way). If earth dna says it developed 300 myo then we know that date is also probable for the other planet.

[Evo]

If earth dna says it developed 300 myo then we know that date is also probable for the other planet.That's not possible. See ryan's expanation of dna above.

[Ryan_m_b]

Ok, thanks.

How about just by looking at the shape and other aspects of the fossil? Would that tell us anything about how we're related to it?

Unfortunately not, morphology arises due to natural selection and wouldn't really tell us much about the biochemistry. I don't know too much about paleontology (http://en.wikipedia.org/wiki/Paleontology) but the advantage of the study on Earth is that we have current organisms to examine as well (useful for studies such as comparative anatomy (http://en.wikipedia.org/wiki/Comparative_anatomy), taxonomy (http://en.wikipedia.org/wiki/Taxonomy), molecular phylogenetics (http://en.wikipedia.org/wiki/Molecular_phylogenetics)).

If we had a really good understanding of Areology (http://en.wikipedia.org/wiki/Geology_of_Mars) we might be able to hypothesise as to the reason for the morphology we see in fossils but unfortunately there will always be a ceiling to our understanding due to the lack of current life. Comparisons to life elsewhere such as Earth won't really help, firstly there could be confusion thanks to processes such as convergent evolution (http://en.wikipedia.org/wiki/Convergent_evolution) but also because the range of possible alternative biochemistries (http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry) are too great. We might be able to get some idea of the biochemistries of pre-historic Martian life but it will be barely a slither of information.

If it's identifiable at all, it will have something in common with earth organisms. If the shape is identifiable (like cilia or vacuoles), similar organs on earth (governed by dna) could imply similar dna influence there too. But I expect that because gravity and chemistry is different, the forms will have developed differently. We can calculate how long ago the organ in question developed on earth to give a time frame for contact (but it could be either way). If earth dna says it developed 300 myo then we know that date is also probable for the other planet.

Unfortunately not, the same and/or similar DNA can have hugely diverse effects on morphology. For example, we have similar Hox genes (http://en.wikipedia.org/wiki/Hox_gene) to almost all animals on Earth but wildly different morphological differences. There is very little that morphology can tell us about biochemistry, the majority of what it can tell us only applies because we only ever deal with life that has evolved on Earth and therefore we have legitimate comparisons.

[bostonnew]

Ok. I guess things are just more complicated than I would like them to be.

But just to be clear, if we found some living microorganisms there, we would be able to determine our relationship with them right? Whether or not we're based on the same amino acids and such.

If it turned out to be based on DNA in the exact same way as life on earth is based on DNA how should we interpret that finding? Would tha necessarily imply common ancestry or could it have evolved independently in parallel?

Thanks

[Ryan_m_b]

Ok. I guess things are just more complicated than I would like them to be.

But just to be clear, if we found some living microorganisms there, we would be able to determine our relationship with them right? Whether or not we're based on the same amino acids and such.

If it turned out to be based on DNA in the exact same way as life on earth is based on DNA how should we interpret that finding? Would tha necessarily imply common ancestry or could it have evolved independently in parallel?

Thanks

I'm hesitant to use the term "relationship". If we found some living organisms then in time yes we could figure out how similar they are to life on Earth. What do you mean if they are "based on DNA in the exact same way"?

If we found that their biochemistry was very similar to ours i.e. utilised nucleic acids, amino acids, lipids and carbohydrates then further study could tell us a few things:

Whether or not some factor of the formation of the solar system led to those chemicals being favoured
Whether or not the chemicals themselves have some properties that make them better ingredients for abiogenesis

If we found it was very similar to ours i.e. Right handed B-DNA with similar coding processes utilising RNA, phospholipid membranes, organelles etc it would be extremely odd.

In my opinion if we did find life it would be highly unlikely that it would show any kind of common ancestor as this would imply some event after abiogenesis led to the transport of life to other planets. I find it unlikely that an event such as a meteorite impact could hurl life to other planets unscathed.