>You see Mars is, a priori, just as likely a place for life to start as Earth.
Asserted without evidence, and considerable waving of hands detected.
Asserted without evidence, and considerable waving of hands detected.
What the author is saying is "theoretically, life could have started on Mars just as easily as it did here".
I think the author was trying to say "I mean, look, Earth and Mars are not that different, and even though we don't have any current evidence for the appropriate chemical conditions on Mars, I don't see why it couldn't have been where life started instead of Earth, because ... well, just because they're sort of similar, kind of. Oh, and next to each other."
In two hundred years, conclusions drawn from what we currently know will be as out of date as conclusions from two hundred years ago are today. Or to put it another way, things known to the best of our knowledge are both as good as we can do and probably wrong because one of the things we know is that historically most of what people know at any given time turns out to be wrong at any given time.
I'm entirely down for our descendants in 200 years laughing at our scientific parochiality, just like we often get to do at our double-century antecedents. But that doesn't justify writing right now that Mars and Earth have a priori likelihoods of being the origin of life in the solar system.
There's plenty of evidence Mars once had much more surface water than it does today. IIRC liquid water is one of the primary preconditions for the evolution of Earth-like life.
What about Mars disfavoured it?
Yes, leaving aside the 20% lower luminosity of the sun[1] a few billion years ago (when Mars had a reasonable atmosphere) putting Mars outside the habitable zone, and Mars's lack of plate tectonics and a protective magnetic field: -
Life certainly could have evolved on Mars. I expect that one day prion-like or viroid-ish molecules may well be found. But so what?
It's one or two billion years from there to a bacterium, let alone a lost civilisation. And Mars did not have the time.
But it would seem to need them for sustained evolution to be possible. So as I said, I'd expect lifeforms at the complexity level of viroids, but not at the level of eukaryotes.
Evolution needs time, lots of time in which conditions don't change too much. (Chemistry that works in dilute solution at 300K doesn't work well at 200K or 500K.) It also needs populations to be able to spread to new areas.
Without a magnetic field, Mars's atmosphere got stripped off. No more liquid water, no more areographical distribution, so no more evolution.
Plate tectonics is needed to ensure that nutrient chemicals don't get locked up permanently in sedimentary rock.
As for the habitable zone, life as we know it needs liquid water on the surface. Mars may have briefly been habitable, but not for long enough.
To be a challenge, the article needs to provide plausible alternative evolutionary pathways that get us eukaryotes without needing these things (time, liquid water, chemical recirculation, limited variability in physcal conditions). It doesn't do that. It's just spitballing.
If early Mars was OK for life to begin, then so was early Earth. We don't need any interplanetary travel.
https://www.nasa.gov/press-release/nasa-confirms-evidence-th...
Yes, life could have 'theoretically' started anywhere where life by definition is possible. Fine, but that's a tautology, and in contrast to what the author seems to believe actually not scientific and thus deserves to be rejected.
If we're talking about scientific statements then show me life actually existing somewhere that isn't earth and then we can make some grounded theories
I mean when you say theoretically and then make a big not necessarily obvious statement you should actually point out which theory you're using.
An "Earthlike" planet is required. Mars may have qualified at one point, but doesn't now.
It is fallacious to assume other life couldn't be different -- we can't prove or disprove that. Likewise, we still don't know exactly how life started here; we simply have a few good theories.
But anyway, this was about SF movies where our heroes visit Arglebarg IV and have adventures with the natives. It's like Victorian adventure stories transplanted into space without bothering to think things through. Let's kill our dysfunctional tropes.
But we.. don't? We just don't have anything to compare to.
https://www.centauri-dreams.org/2015/04/16/g-hat-searching-f...
“Our results mean that, out of the 100,000 galaxies that WISE could see in sufficient detail, none of them is widely populated by an alien civilization using most of the starlight in its galaxy for its own purposes. That’s interesting because these galaxies are billions of years old, which should have been plenty of time for them to have been filled with alien civilizations, if they exist. Either they don’t exist, or they don’t yet use enough energy for us to recognize them.”
there is an implicit part of our definition that includes timescales and size, and this puts some limits on the type of chemistry that can be involved in order to qualify.
if you open up the definition to be things that work on totally different timescales and sizes than we consider, then i think its fair to say that the chemistry doesn't need to be similar at all.
but for things that form blobs of life on the rough range of scales found on earth, and that "do stuff" in the range of timescales that we see on earth, there are not too many choices. silicon often gets touted as an alternative because of its ability to form branched structures. do you know of any other ideas?
dna is mostly a 4-note tune, and computers, the potential precursor to artificial life, 2. i'm sure something as vast as the universe can come up with a little more variation than skin type in those tiny little gaps.
ps. I have my Artificial Life III conference t-shirt from 1994 :)
If you’re thinking of planets that are not similar to Earth, of course all bets are off.
I think GTP-powered file is possible, even the glucose metabolism produce one GTP (and many ATP). (Perhaps I'm missing something, Chemistry is not my main specialty). Perhaps it is even possible to have NADH-powered life, but it is more different so it may be impossible.
> ossified calcium-braced
Diatoms use silica, insects have a protein exoskeleton, and octopus are weird.
> oxygen-absorbing, [...] protein-enriched, [...] water blobs
I guess these three are safe bets (with a little different selection of amino acids).
Edit: Also, the article you linked specifically states "Scientists debate a range of ideas about how life on earth began", undermining your first point.
https://en.wikipedia.org/wiki/Mars
Had to look this up. Seems like there is the same temperature window available on Mars that is needed for life on earth.
When mars was wet, geologically a GI d and still had an atmosphere the temperatures would’ve been much closer to earth today.
Considering the best evidence of Mars being conducive to earthly life formation is the likelihood of it more closely resembling earth's conditions in the past, it doesn't seem like the sort of claim likely to resolve issues with earthly primordial soup hypotheses...
One thing we know (almost) for sure is that no new forms of life have emerged on Earth for hundreds of millions of years. So we should expect that the conditions required are quite special indeed, or the event is extraordinarily unlikely. As such, it is silly to assume that any other planet is "similar to Earth" in the ways that matter for life appearing based on simplistic observations (temperature, distance from the sun, existence of the most basic required elements).
My point is that, despite the huge abundance of life on Earth today, it is all based on a very old abiogenesis event, with all indications that it was more or less a singular event.
All life on earth seems to be part of the same philogenetic tree, so it seems that life appeared once and then kept evolving from that initial life-form. Of course, there is a good chance that there was some variety of initial organisms that either merged together in symbiotic relationships, such as mitochondria with the rest of the cell, or got out-competed by the one type of organism that we are all descended from. This still indicates that life arose in a single place and only over a relatively short amount of time.