Life Exists in the Driest Desert on Earth. It Could Exist on Mars, Too | Hacker News Reader

Life Exists in the Driest Desert on Earth. It Could Exist on Mars, Too

futurism.com

49 pointsSirLJ56 comments

I do not understand the consistent assumption that life on other planets must take a chemical and physical form similar to our own. Given the myriad of unique chemical compositions and the seemingly infinite ways in which information may be stored and propagated as molecular data, I feel it is myopic to constrain our search for life to such a narrow chemistry.

Sure, I understand that given limited resources it is sensible to look for what we know works, but I guess what I'm getting at is that articles which infer potential for life on other planets based on earth-bound extremophiles are probably not as substantial as they may seem.

I suppose time will tell.

If you assume that physics works the same on other planets then carbon-based life is simply the most likely simply from the chemistry we know about. Speculation about say Si based life isn't new but nobody has come up with how that type of organic chemistry might plausibly work.

but then, do chemists really know how carbon based life works really? if it weren't for the living examples, wouldn't it be just as hard to work out how proteins form and so on?

It isn’t about knowing how carbon life works but understanding basic chemistry which we do.

Carbon is the atomic floozy it will hook up with a lot of other elements and can form relatively strong bonds, and it can have upto 4 bonds per carbon atom nominally.

This makes carbon the star of its little own chemistry show.

Silicon is similar to carbon in this regard which is why it is in the same column in the periodic table however it bonds with fewer elements and it’s chem requires more energy and is often less stable.

This is what the grandparent question always skips over.

"Why not alternatives to organic life?"

Underestimates the fact that, as near as we can tell, building life from organic molecules is easier (and substantially so).

Given that life seems to be a relatively rare event sequence, and that organic life is the easiest form we've been able to figure out from chemistry (ne physics)... betting on another kind is a long shot.

Granted, maybe we've missed something obvious. Maybe our understanding is critically flawed. But from everything we know right now, one can't just handwave and say "Well, many kinds of life are possible."

Indeed, currently there is no replacement for organic chemistry for life because it seems that we can't find another combination that would be as flexible and stable as carbon.

Silicon can replace carbon in a few scenarios but it isn't likely enough for any plausible mechanism that would support life to be based on silicon alone.

This is why likely all life is carbon based, some of the other elements like phosphors vs arsenic have more wiggle room but there is simply no "glue" other than carbon and this is simply due to physics not lack of imagination or knowledge.

Has there been any thought given to the possibility of life at the subatomic level?

Yes not possible not enough complexity or stability for that matter and the energy levels required are well explosive the smaller you go the more energy is needed since you essentially go form gravity (macro) to electroweak (molecular and atomic) to the strong nuclear force (subatomic) and there is a pretty big increase in magnitude of the forces that govern interactions between each phase.

Heck even within the unified electroweak force there is a huge range e.g. burning coal releases he energy in the stored covalent carbon bonds which are tied by electromagnetism part of the electroweak force but if you start breaking protons a part from neutrons which is the weak force you get a nuclear bomb.

Life needs bonds that are cheap to create, cheap to break and ones that don’t explode once you do break them.

To bolster your other response: in college chemistry classes are split into two kinds: “organic chemistry”, and “everything else”. But he term “organic” in this context means “compounds with carbon atoms”. There are so many ways that carbon bonds to other atoms, and in such complex configurations that there are classes reserved for this single element. And as undergrads will tell you, these are the hard classes!

There's an entire Wikipedia article on alternative biochemistries [1].

Quoting that page, with regards to Si: However, silicon has several drawbacks as an alternative to carbon. Silicon, unlike carbon, lacks the ability to form chemical bonds with diverse types of atoms as is necessary for the chemical versatility required for metabolism. Elements creating organic functional groups with carbon include hydrogen, oxygen, nitrogen, phosphorus, sulfur, and metals such as iron, magnesium, and zinc. Silicon, on the other hand, interacts with very few other types of atoms [...]

[1] https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi...

Organic chemistry isn't required. I can easily come up with one mechanism: What if AI is a common development for advanced organic life forms, after which those organic life forms die out, but silicon or otherwise non organic life forms continue on and move out to other planets?

We have SETI for that, and Mars isn't a likely place for advanced technological life to be hiding out on.

I’d really hope that physics work the same on other planets. If that were not the case, we’d have a fundamental problem with our understanding of the universe.

That would actually be really exciting. In trying to resolve where we had gone wrong, we'd learn even more about how the universe works. Our current theories still have holes (no pun intended)

Perhaps a bit arrogant to presume that something is unlikely to exist simply because we haven't yet conceived of it.

Look at the complexity of life on earth alone. There's plenty that neither you nor I will ever even imagine.

Anthropic principle, probably.

But... the universe is filled with water, so that's a likely medium for chemical reactions. And if you want long molecules to actually do interesting things, you need carbon in there somewhere. So the most likely chemistry is at least somewhat similar.

And for Mars, which is made out of similar stuff as Earth, and periodically trades rocks with us? If there's life on Mars, it probably shares ancestry with you and me.

> I do not understand the consistent assumption that life on other planets must take a chemical and physical form similar to our own.

I always pondered about this as well. I came to the conclusion that, given the sheer number of celestial bodies (e.g. planets) in the universe, restricting our gaze to only the ones that can sustain life as we know it (i.e. carbon-based bags-of-mostly-water) restricts the search space considerably.

I don't know whether that actually increases our likelihood of finding extraterrestrial life; I certainly do hope so.

There are two spaces to consider. One is the range of habitats available, the other is the range of chemistry complex and rich enough to form viable metabolic pathways.

The problem is the OPs comment about restricting ourselves to a narrow range of chemistries is a bit naive. Carbon chemistries are so rich and so complex it's a whole field of study alongside all other forms of chemistry put together. That's not just because it happens to be interesting because we are made of it, it's just a fact of chemistry and physics that carbon chemistry is fantastically diverse and scalable compared to all other known and theoretical chemistries.

A lot of somewhat simplistic conjecture starts from the idea that the universe is vast and unknown and could contain 'anything'. But the fact is we can see the universe through our telescopes and other instruments. We know what all the elements are and what their properties are so it seems rational to use that information to optimise our search.

After all, if there are unknown elements and unknown chemistries or structural paradigms out there that might also be viable, since we don't know what they are, we also don't know what to look for to find them, so that avenue of speculation doesn't actually take us anywhere useful.

As you mentioned, for the life as we understand it you need complex yet flexible enough molecules. And looks like carbon because of its chemical properties fits the bill for the best basis for them.

I don't know about the physical form - the physical form of life on earth is pretty diverse IMO.

But as far as the chemical form goes, my limited layman's understanding of why life is most likely to be carbon-based, is as follows.

The universe is mostly made up of hydrogen, helium, oxygen, and carbon/nitrogen. Other elements also feature, but those four are typically the most abundant. If there is any life at all in the universe, the likelihood is it will comprise of these common elements. Humans, for example, are mostly (96%!) hydrogen, oxygen, carbon and nitrogen (see https://en.wikipedia.org/wiki/Composition_of_the_human_body).

But what about helium! Helium is uninteresting because it is not very reactive, so the ways it can interact and "be stored and propagated as molecular data", as you very nicely put it, is quite limited.

Which brings us to carbon, which is quite reactive. It reacts with itself and gives you diamonds, graphite, buckyballs, graphene, nanotubes. It reacts with the most abundant chemical in the universe and gives you hydrocarbons. Sprinkle some nitrogen and oxygen in the mix - also very common elements - and you got yourself proteins and fats and carbohydrates and amino acids and whatnot.

So just based on that, it's more likely than not that life would be made up of hydrogen, oxygen, carbon and nitrogen, with carbon in the central role. That is not to say that there couldn't be silicon-based life, for instance, but it's just not as common an element as carbon.

That's five elements -- nitrogen and carbon are different elements.

The reason we know that life on Mars (if it exists) must be similar to life on Earth is because both have been peppered with rocks from the other knocked off by meteorite impacts (from memory something like 100kg from Mars to Earth per year and 1 kg the other way around).

Some of these rocks have been ejected under benign enough conditions (and protected during transit) to enable microbes to make the journey alive. I think if we do find life on Mars we might be rather disappointed to find that it is exactly like life on Earth.

There is an interesting hypothesis that life arose on Mars and was later transferred to Earth. One of the reasons for thinking this is that life seems to have appeared almost instantly on Earth as soon as it cooled down enough for there to be liquid water. Mars being further out from the sun (and smaller) likely had liquid water well before the Earth.

..or that both have an external source.

Imo, if panspermia is proven and (for extra points) that it exists/ed on mars.... It becomes likely that earth and mars aren't the only 2.

Any proof of this would be huge. We could frame the whole Drake's equation I panspermia terms and get clues on where to look and what to look for.

And considering we still have no signs of mega-engineering structures, interstellar probes or otherwise interstellar broadcasters, it would increase the likelihood for a great filter to be ahead of us. Constraining the last terms of the equation.

Aside from the point others have made that carbon based chemistry is a likely candidate for life, there is another factor I think:

We already know that carbon based can exist and we know what it looks like. Since our means for searching for life in the rest of the universe are still very limited, it is best to focus on what we know, instead of searching for a different form of life of which we

* don't know what it looks like

* don't know whether it can exist in the first place

I think the field is potentially wide even within carbon chemistry. Genetics (which seems to have a single origin) could feasibly exist as a completely different yet still carbin-centric "implementation."

Yes. If we define life as something that lessens local entropy, then the possibilities are vast indeed.

Agree, it's an interesting question.

I think the problem is knowing how to define "life" and then working back to other possible implementations. As Douglas Adams framed it, "does it go squish if you step on it?"

As far as I know, the current thinking is still that life emerged (or arrived) only once on earth. One version of genetics, one implementation of life's basics, the eath-life basics. This makes it hard to generalize. It's also hard to speculate on the likelihood of such a seed event, on the basis of a single occurance. We have very little information, in Drake's equation terms, on the likelihood of life emerging given earth-like circumstances. Earth is obviously life-supporting. Why did it only happen once here, and so early in the game... As soon as the planet cooled.

For example, we could define life in terms of evolution, any evolutionary system with potential for a lot of complexity in the long term. ...we only have one example of this, earth life.

I think it's natural to start here, with earth life because that's all we know about and our speculations are very... speculative. At least we know what we're looking for this way. Earth-life can survive X conditions, therefore life can. What conditions can other types survive, if they do or even can exist? Who knows.

A lot of mystery still. Even the emergence or pan-spermia question is wide open. Even within this information bubble of earth life.. we don't know how extreme life can get. We just know about stuff that evolved to survive the extreme conditions found on earth. It's plausible (even probable) that earth-life has the potential to go even further, if earth provided more extreme niches to adapt to.

In addition to the other fine points: A fundamental job of a life form is to pump entropy out faster than the environment can pump it in. This tends to eliminate any hot environments, such as stars, the insides of active planets, and one of my personal favorite science fiction life forms, neutron stars and other such exotica.

A life form must also be able to develop to some reasonable level of complexity in some reasonable period of time in order to be alive. This tends to eliminate old stand-by favorites such as nebula, very cold planets like Pluto, and the interstellar medium. It doesn't matter if they got a 12 billion year head start on us if they "live" a billion times slower than we do. (And if you start doing the math on how cold things are and how often particles interact in even a nebula, let alone an interstellar medium, it doesn't take long to see that a billion times slower is actually me being quite generous.) It is likely that at the time scales an interstellar life form would live at, the interstellar medium is too frequently disrupted by novae and such for anything to live in it.

So you pretty much end up limited down to roughly the temperature range we're familiar with pretty quickly just based on thermodynamic considerations. Given that you also have to add in the fact that chemistry must be able to support the life form, you end up with the result that life really isn't going to be that hard to identify, even if it's based on ammonia or something. It'll still be pretty obvious that something life-based is taking place.

One of the other things about this conversation is I think "a bit too much science fiction" can lead people to think that Earth life is somehow pedestrian or something, but in reality, Earth life is incredibly diverse and has covered almost every imaginable niche on this rather diverse little planet, and that makes the odds of meeting something that has literally no Earth analog pretty long. We could meet a planet of ammonia-based silicon life forms and it could very well be the case that we'd still recognize every player in the ecosystem just fine on sight, because we've got a lot of terrestrial data points as to what might constitute a viable life form. "Life forms that could exist in this universe that looks nothing like Earth life" may very well be a nearly empty set. (Or at least life that could naturally evolve. One could hypothesize a machine civilization in a lot of places, but it's hard to see how such a thing could evolve directly and biologically.)

>In addition to the other fine points: A fundamental job of a life form is to pump entropy out faster than the environment can pump it in.

Yes. From a chemistry perspective, this requires a membrane, or barrier, that separates "life" from "non-life". It also requires mass transport across that barrier in both directions, which would presume liquid inside that barrier. A third variable is the mass of the planet, which dictates which molecules can be present in the atmosphere, and the temperature, which dictates physical states. The requirement for a barrier and mass transport via liquid already imposes restraints on the chemistry that rule out most of the periodic table. Metals lose their electrons too easily. After metals, you're not left with much to work with. Carbon compounds in water is still the best idea we have. Simple long chain carboxylic acids spontaneously make membrane-like micelle structures in water. If anyone has any better ideas, there's a Nobel Prize for the first person to create life from non-life. Go for it.

But this leaves pressure and specific volume out of the equation, does it not? Lots of molecules can be liquid in the right environment.

Sure, which is why environments like Europa are exciting.

Why would it presume liquid inside the barrier and not simply a fluid (including e.g. gasses)?

A lot of the chemical reactions required to maintain life as we know it involve charged intermediates. These are not generally soluble in the gas phase as they have very low vapor pressures.

There are some fundamental chemistry reasons why, no other element is like carbon in it's ability to bind and react in so many ways, so carbon based is the most likely thing. Maybe not the only.

if your definition of life is that broad then God could also exist

It is very likely life on earth evolved under more optimal conditions and then adapted to drier and more extreme ones. Was Mars ever hospitable enough for long enough for life to evolve is the question.

Nope! First signs of life are found on Earth in very early minerals that existed under extremely brutal conditions back then. They're also found in oldest parta of crust that we have.

well, AFAIK we still have no idea whats actually needed for life to form.

Also the conditions for life were better on mars in the past so its entirely possible that life existed and kept on going on mars.

Nah. The question is if life could feasibly hop from a meteor impact on Earth over to Mars.

That is a lot less likely than the other way round, as the atmosphere of Earth and its greater proximity to the Sun makes it immensely more difficult to launch a rock from the surface all the way to Mars.

While a rock launched from the surface of Mars, once it has escaped the planet's gravity well without encountering significant drag from the atmosphere, can just "fall" to Earth.

Gaining and losing orbital energy are both equally hard in the vacuum of space, it's not harder to get from Earth's orbit around the Sun to Mars's or vice-versa - though it takes somewhat different amounts of delta-v to go to an Earth-Mars intercept from them. The reason it's easier for ejecta to get from Mars to Earth than vice versa is that Mars has a shallower gravity well to climb out of before making the inter-planetary trip. It's a lot easier for an impact to impart the ~6 km/s velocity you need to get from the surface of Mars to hitting Earth's atmosphere than the ~13 km/s it takes to get from Earth's surface to hitting Mars.

"Why Alien Life Would be our Doom - The Great Filter" Great short video from Kurzgesagt – In a Nutshell

https://www.youtube.com/watch?v=UjtOGPJ0URM

This is why whenever I see news like this, I get nervous.

Life arose very quickly on Earth after it cooled down. Photosynthesis took longer and Eukaryotic life took longer still. Seeing a Martian protozoa that evolved independently of Earth life would be scary. Bacterial mats around a thermal vent not so much.

https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_h...

EDIT: It's also sort of scary to think that it took 4.5 billion years from the first life for us to evolve, and it's only going to be another billion before the growing sun sterilizes the Earth's surface.

Life _could_ exist anywhere, even in deep space, but apparently it doesn't. You could probably interpret some behaviours of neutron stars as life.

I admire the human drive to solve the cosmic puzzle, find something bigger and more meaningful than us, but so far it looks like there is only one place in the Universe that has life. And even planets with relatively favourable conditions like Mars are dry, lifeless husks devoid of any, even the simplest lifeforms.

Life almost definitely exists elsewhere, and this is coming from a religious person. The number of star/planet combinations out there virtually guarantees it mathematically. The problem is that space is too large and vast and the speed of light too "slow" to be able to reliably "scan" the universe fast enough to find life.

Two scenarios (at least):

1. God exists and specifically seeded life on Earth.

Even if this is the case there is still no reason meteorites couldn't carry microbes from Earth to Mars. It doesn't seem like God cares about quarantining life to earth, seeing as we made it to the moon.

Also, why bother making a universe so mindbogglingly huge and vast only to put life on a single planet? Makes more sense for God to seed countless planets out there with life. And indeed there are a few verses in the Bible that imply Earth is not God's only creation.

2. God does not exist and life emerged naturally.

If this is the case then that means life can emerge naturally somewhere else with identical conditions, and given the number of stars/planets/time elapsed, this seems like it could be a high probability (hard to know, though, without understanding exactly how life emerges).

I've seen this "argument from big numbers" lots of times and it's unconvincing. The large number of planets in the universe means nothing if none of them have Earth-quality conditions, or if it's purposefully kept empty, or if the probability of life arising is too small even given the large number of planets.

Big numbers don't "guarantee life", rather they make it "very unlikely there isn't life". It is the same way that "an absence of evidence is not evidence of an absence".

Secondly, it remains a challenge to categorize and define the envelope for what is and isn't "life". We have a decent hold on "earth-like life" but it will not be sufficient for all that might be encountered in due time (or already exists unbeknownst to us). If you have ever defined an ontology you know that it becomes more and more challenging to put definitions to the universals as you climb up the ontology. At the top, the universal from which all other universals inherit is very commonly left descriptionless.

Last, there are many alternative to the Christian One-God view that you express (I am sure you are aware and chose to limit your points for brevity). There are spiritual books that explain/propose/posit the universal disconnect between the living conscious beings of Earth in this material plane and the myriad of "beings" that exist in other higher dimensions/levels/shells.

"very unlikely there isn't life" == "very likely that there is life"

As we keep sending probes to Mars, maybe some of the toughest forms of life might be transported to Mars and become Martian before human does

If any kind of life exists on Mars it would have to be unlike anything here. Mars is bathed in peroxides and a whole spectrum of ionizing radation with little to no magnetic field to protect it. https://www.ncbi.nlm.nih.gov/pubmed/11537371

There are many organisms that can tolerate those concentrations of peroxides, and others that can tolerate the radiation exposure aside from the fact that a few inches of soil provides fairly decent protection anyway.

From your link: "These results indicate that it is doubtful that the presence of H2O2 alone on Mars would make the surface "self-sterilizing"."

Sorry about that, this link from nature is a better angle to the problem (I forgot about perchlorates on Mars). https://www.nature.com/articles/s41598-017-04910-3

looks pretty brutal up there

At some point we will be asking ourselves - is it a good idea to bring those alien life samples back to earth for analysis.....

Even the driest desert on Earth has more atmosphere than Mars.

Reply on news.ycombinator.com