So, life on Mars...

[The Firebird]

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.

I mean that Earth and Mars had similar chemistries that caused life to be funneled down similar trajectories from different origins. Not that life transferred from one to the other. But even that idea is quite interesting...borate is an important stabilizer of ribose, and more common on Mars than Earth. I know some people have invoked a Mars-first idea on those grounds.

 

[Reynard]

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.

Right, but the important part is that if panspermia is found to be true here, we are stuck with having no idea how common it might be for life to arise independently, and therefore no additional information on how abundant it might be in the wider universe. But if we find that microbial life evolves pretty anywhere it is possible given enough time, that paints an entirely different picture.

 

[Dannyalcatraz]

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

Which begs the question: what is the reentry velocity of an unladen meteorite?

 

[Morrus]

Which begs the question: what is the reentry velocity of an unladen meteorite?

What do you mean, an African or European meteorite?

Wait, that doesn't work.

 

[trappedslider]

 

[Umbran]

What do you mean, an African or European meteorite?

Wait, that doesn't work.

Well, insofar as it can happen the other direction, too we can expect that rocks from Earth have ended up on Mars, too.

 

[Mustrum_Ridcully]

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.

That is kinda what I wonder about.
Just like we could maybe theoretically envision something like silicon-based instead of carbon-based life based on carbon and silicon being in the same column on the periodic table. But when we look more closely, we find that silicon-based bonds do lack some of the stability that carbon-based bonds have - they are similar, but not similar enough. Also - carbon is still way more common in the universe than silicon.
And once we settle for carbon-based life - There might be million different nucleic acids, but overall, only very few work really well as building blocks for life.
And on some level, this makes sense, doesn't it? If life exists, it makes more sense if it is based on building blocks that are common or easy to create by accidents, rather than exotic and unlikely to happen.
Though it's also not always the most common - carbon is still less common than hydrogen or helium. And we use some rarer elements, too. And the sun itself is a common type of star, but there is another type of star even more common. A variation of "Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away"?

 

[The Firebird]

That is kinda what I wonder about.
Just like we could maybe theoretically envision something like silicon-based instead of carbon-based life based on carbon and silicon being in the same column on the periodic table. But when we look more closely, we find that silicon-based bonds do lack some of the stability that carbon-based bonds have - they are similar, but not similar enough. Also - carbon is still way more common in the universe than silicon.
And once we settle for carbon-based life - There might be million different nucleic acids, but overall, only very few work really well as building blocks for life.
And on some level, this makes sense, doesn't it? If life exists, it makes more sense if it is based on building blocks that are common or easy to create by accidents, rather than exotic and unlikely to happen.
Though it's also not always the most common - carbon is still less common than hydrogen or helium. And we use some rarer elements, too. And the sun itself is a common type of star, but there is another type of star even more common. A variation of "Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away"?

Yeah, I find the interplay between determinism and chance super fascinating here. Another idea is the evolution of oxygenic photosynthesis. Oxygen (and water) is great energetically; there is competition from fluorine and chlorine but those are both incompatible with carbon biology for other reasons. So any water based life will naturally want to end using water as a reductant.

But because of those energetics it is hard to use of water; you need something with a lot of redox potential. It took some 2 billion years to evolve the ability to use water, via a complex manganese catalyst. It might be that any multicellular life has to develop something like photosynthesis on the way, dictated by energetics. And based on redox potentials, there aren't many alternatives to manganese. So if you do see life, at least complex life, elsewhere, it may not look very different.

There are a number of chokepoints like this...also e.g. the evolution of eukaryotes, which happened just once.

 

[Bohandas]

Gotta get those samples back to Earth and study them properly!

Isn't that how every horrot movie starts?

(but more seriously, they'd get contaminated)

 

[Whizbang Dustyboots]

Isn't that how every horrot movie starts?

It was super confusing in the Amityville Horror.