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Would Earth plants grow in alien soil?
June 1, 2011 7:38 PM   Subscribe

Suppose there were another Earth-like planet with an Earth-like ecosystem, but evolved totally separately from Earth's. Am I right in suspecting that we would almost certainly not be able to digest any of its plants or animals and vice versa? If we were to bring our own plants, could they grow in the soil?

This is a question that has been bugging me for a long time. Sadly my biology skills are high-school level at best, so I don't trust my own answers at all. My thinking is that Earth animals couldn't eat alien plants or animals, but that Earth plants could grow in alien soil.

I suspect that we wouldn't be able to eat the plants or animals because there's no reason to think the aliens would use the same set of amino acids we do, right? I am definitely hazy on how things work at that level, but my understanding is that the particular amino acids that humans care about derives at some very low level from the universal genetic code, and that there's no reason to suspect that alien DNA would use the same coding scheme. Thus we couldn't count on our digestive systems being able to use (and/or not be killed by) the acids produced in alien biology.

Plants seem like a different case to me, though. Seems to me that plants wouldn't be counting on particular acids being available in the soil, and they'd be working more directly with minerals in the alien soil, which would presumably be similar to the minerals in Earth soil. So they could grow normally, and then we could eat those plants just as though they'd been grown on Earth.

Does any of that sound plausible?
posted by jacobm to Science & Nature (14 answers total) 9 users marked this as a favorite
 
NASA is actually currently working on plans for genetically engineered plants for Mars.
posted by Cool Papa Bell at 7:43 PM on June 1, 2011 [1 favorite]


Am I right in suspecting that we would almost certainly not be able to digest any of its plants or animals and vice versa?

One potential showstopper is protein chirality. All of the amino acids on Earth are "left-handed," but this is arbitrary. If life on the pseudo-Earth evolved with "right-handed" amino acids, then while you could possibly digest the plants and animals in some sense you couldn't derive adequate nutrition from them and would eventually starve.

Seems to me that plants wouldn't be counting on particular acids being available in the soil, and they'd be working more directly with minerals in the alien soil, which would presumably be similar to the minerals in Earth soil. So they could grow normally, and then we could eat those plants just as though they'd been grown on Earth.

Many Earth plants have complex relationships with nitrogen-fixing bacteria and symbiotic fungi in the soil. You'd have to bootstrap the whole soil ecosystem, probably by bringing a bunch of topsoil along with the seeds.
posted by jedicus at 7:46 PM on June 1, 2011 [1 favorite]


Another potential issue is the relative availability of minerals. If the pseudo-Earth plants and animals contained a disproportionately high amount of, say, potassium, then getting enough calories might mean getting toxic amounts of potassium. There are several elements that are purely toxic to humans and have no known biological function in humans, including arsenic, mercury, and lead. If the pseudo-Earth animals and plants used these then they would be useless as food.
posted by jedicus at 7:54 PM on June 1, 2011 [1 favorite]


Not an answer as such, but Larry Niven addresses this as one of the plot points for his novel Destiny's Road
posted by namewithoutwords at 8:02 PM on June 1, 2011


Another potential problem is how symbiotic / dependent we are a whole host of unicellular lifeforms, for lots of basic functioning. These relationships are poorly understood as present, so it's best to bring plenty of our own dirt with us, when we go!
posted by gregglind at 9:14 PM on June 1, 2011


Regarding growing plants on alien planet, you don't have to grow them in the soil; you can grow them using hydroponics set-up, where all the plants need will be sun-light, carbon-dioxide, water and plant-food (nitrogen, phosphorus and other trace minerals). To practice agriculture on an alien planet may be difficult, because you will have to worry about soil condition, interaction with other flora and fauna, diseases and pests; just like we do here on Earth, except more foreign.

As for eating alien plants/fruits/animals; it'll be also difficult. We can't eat everything on Earth either, mainly because of toxins. However, I believe that with some minor processing (more than just cooking), it may be possible to turn alien food into consumable nutrients. Our body pretty much only need oxygen, water and sugar; plus other supplements in trace amount (like calcium, iron and vitamins). We are capable of synthesize 1/2 of the amino acids type we need, so we will also need to supplement our intake with Earth-based protein source (plant or animal source); but otherwise, I think it's possible to process alien (carbon-based) food-stuff into sugar and subsist from that.

See: http://en.wikipedia.org/wiki/Essential_amino_acid
posted by curiousZ at 9:53 PM on June 1, 2011 [1 favorite]


You can grow plants in totally sterile mixes of minerals etc. These mixes of minerals and what have you can be produced by the chemical weathering of rock, glacial action etc. You do not have to involve an organic agent along the way.
posted by wilful at 10:28 PM on June 1, 2011


You're doing it just fine. If you happen to be a Babel fish, you can live off the brainwaves of just about any creature. Unfortunately lifeforms tend to vary a great deal, and if you happen to crash-land on Sqornshellous Zeta, inhabited solely by semi-intelligent mattresses, you will likely have a very hard time surviving no matter what you are.

To answer this semi-seriously, alien DNA certainly would not have the same set of amino acids, or even use them at all, but it's possible that it could share a subset of them. Amino acids are simple enough to be produced randomly, whether in the Miller-Urey experiment, or out in space. The same goes for whatever these alien organisms used to store energy - glucose is extremely simple, and fairly handy for that purpose, so convergent evolution could lead to its use. On the other hand, it could easily lead to something different that would be completely unusable. (At least, as far as I know. This is not my field, and sugars could be a universal constant or an incredibly improbable mechanism.)

It's also worth noting that Earth's atmosphere today only exists due to the extremely dramatic changes wrought by early life. If parallel-Earth doesn't have something in the neighborhood of 20% O2, .05% CO2, 79.5% N2 due to equivalent processes, neither Earth flora nor fauna are going to fare very well.
posted by marakesh at 1:23 AM on June 2, 2011


All of the amino acids on Earth are "left-handed," but this is arbitrary.


The evolution of chirality might not have been arbitrary.

posted by Blazecock Pileon at 1:34 AM on June 2, 2011 [1 favorite]


As you suggest already, this depends on the chemical building blocks of the alien vegetables. No only would they have to have (mostly) the same amino acids, but they would have to be based on proteins made from amino acids in the first place, together with other standard building blocks of life on earth, nucleic acids, fatty acids, (poly)saccharides and so on.
The big question, and one I doubt can be answered, is how likely it is that independently evolved life would be made of the same basic compounds. It would be as possible that there is just not much wiggle room to make complex organisms under the physical properties which are completely unlike the ones on earth, but it is as possible that a whole planet ecosystem is based on something entirely different. The chemistry leaves so many possibilities that I doubt anyone can make predictions as to the likelihood of either.
After you figure that out you can think about the details, like which amino acids would be there, and how much of a different array of metabolites would be toxic to an earthling.
posted by Lynx at 1:53 AM on June 2, 2011


The plants might be able to grow in rock dust on another planet.
posted by delmoi at 1:55 AM on June 2, 2011


The big question, and one I doubt can be answered, is how likely it is that independently evolved life would be made of the same basic compounds.

This is precisely it. With a sample size of one, we have no idea what aspects of our biochemistry are arbitrary and which are universal (or at least likely) for fundamental reasons.

I think we can speculate with some grounds that alien life forms would be carbon based for pretty fundamental reasons which have to do with ways to make large molecules. The other suggested building block of life is silicon, which is similar but much heavier and probably not as good for various reasons.

Hydrogen is also likely to play a part, just because it's so abundant. Also, a highly electronegative element like oxygen, fluorine, or nitrogen to play a part in redox reactions (which are a great way of moving energy around).

They might well have some kind of folding polymer biochemistry analogous to our proteins, but I'm not sure that there's any reason to assume that they'd use amino acids for this. Or that if they did, they used the same ones we do.
posted by atrazine at 3:48 AM on June 2, 2011 [1 favorite]


There are a lot of benefits to the whole DNA / amino acid method of biochemistry such that it may be more universal than you'd first think.

To be a viable ecosystem, your genetic material needs to strike a careful balance where it is available for protein (or whatever) production and reproduction, but is durable enough so that it doesn't just fall apart the first time the sun shines on you. Three letter words (codons) from a four letter alphabet (A, C, T, G) make a lot of sense from in information theory point of view. There is a lot of redundancy in the way the codons are set up, so that if you have an error, it is often silent - yielding the same amino acid as the correct DNA would. Longer words with fewer letters or shorter words with more letters would make for a klunkier system, either in terms of the size of the genetic molecules or the amount of hardware it would take to make all the different bases.

Also, at some point I saw a paper that suggests that RNA codons stick to the amino acids they code for preferentially, so that may be the mechanism for protein production in very early life. So it could be that there aren't really any other potential base pairs that interact within the necessary parameters.

On the other hand, there's not really been a big market for coming up with a complete hypothetical biochemistry driving the supercomputer equipped molecular modeling crowd, so it could also be a lot easier than you'd think.
posted by Kid Charlemagne at 6:38 AM on June 2, 2011


The evolution of chirality might not have been arbitrary.

Fair enough, but it's at least imaginable for life to have evolved with right-handed amino acids.
posted by jedicus at 6:56 AM on June 2, 2011


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