How long to bootstrap a marine ecology?
January 15, 2010 5:39 PM Subscribe
Astronomers discover an extrasolar planet, identical in climate and material composition to Earth, on which life happens never to have arisen. We pack a few kilos of cryopreserved plankton into a space probe programmed to crash into the largest body of salt water. How long does it take this advance crew to populate the oceans?
This imaginary planet has land and sea, water in all three states, volcanoes, ice caps, weather. It has a hydrological cycle; there are plenty of dissolved minerals in the oceans, and lots of finely-ground sand. We won't need to capture comets or bore moholes or set up giant orbiting mirrors; this place has all the basic material needs of an Earth-like ecosystem, and all we need to do is bootstrap that ecosystem.
- how long would it take for a kilo of pure algae to colonize an entire oceanic system?
- how long would it take for a kilo of mixed phytoplankton and zooplankton to colonize the same system?
- is it possible to include enough genetic diversity in our hypothetical kilo container for an indefinitely self-sustaining ecology?
- more generally, if you were to introduce a predator species and a prey species into the same ecosystem, how would you calculate the ratio of predator to prey in order to minimize the possibility of extinction?
- assuming you've waited long enough for the seas to fill up with microscopic life, what do you send in the second probe?
This imaginary planet has land and sea, water in all three states, volcanoes, ice caps, weather. It has a hydrological cycle; there are plenty of dissolved minerals in the oceans, and lots of finely-ground sand. We won't need to capture comets or bore moholes or set up giant orbiting mirrors; this place has all the basic material needs of an Earth-like ecosystem, and all we need to do is bootstrap that ecosystem.
- how long would it take for a kilo of pure algae to colonize an entire oceanic system?
- how long would it take for a kilo of mixed phytoplankton and zooplankton to colonize the same system?
- is it possible to include enough genetic diversity in our hypothetical kilo container for an indefinitely self-sustaining ecology?
- more generally, if you were to introduce a predator species and a prey species into the same ecosystem, how would you calculate the ratio of predator to prey in order to minimize the possibility of extinction?
- assuming you've waited long enough for the seas to fill up with microscopic life, what do you send in the second probe?
However long it took life to advance on earth? Probably longer than a human lifetime. Maybe 2 human lifetimes.
Logically wouldn't there already be life on that planet of some kind?
Assuming the conditions appear perfect for earth-like life, and there is none, I imagine that whatever unseen force kept life from establishing itself on that planet would probably kill off whatever life you try to introduce.
If you introduce a species of predator / prey into an ecosystem with no other life, what is the prey eating?
posted by outsider at 5:50 PM on January 15, 2010
Logically wouldn't there already be life on that planet of some kind?
Assuming the conditions appear perfect for earth-like life, and there is none, I imagine that whatever unseen force kept life from establishing itself on that planet would probably kill off whatever life you try to introduce.
If you introduce a species of predator / prey into an ecosystem with no other life, what is the prey eating?
posted by outsider at 5:50 PM on January 15, 2010
Best answer: a) What mr_roboto said. Free O2 will be hard to come by, so you'll have to start with anaerobic species, preferably ones that produce O2 as a byproduct
b) Once you drop them into the ocean, they're out of your control. Thus, there's no guarantee that the evolutionary pathways followed by Earth's early inhabitants will be similar there (in fact, it may be rather unlikely). You can stack the deck, but a few mutations and a slight competitive advantage may be all it takes to swing the entire ecosystem into producing massive quantities of methane and CO2, instead of oxygen. A few million years of that, and you end up with Venus, not Earth.
c) Along a similar note, due to the small size of the seeded population, I imagine that you're as likely not to hit an extinction event which wipes out everything. Imagine a simple system, where one species photosynthesizes and the other eats them. If the predators gain even a slight growth advantage, they'll quickly wipe out the base of the food chain, and consequently starve to death.
d) assuming that none of these things are problems, and that growth conditions are ideal, your population will enter an exponential growth phase until some resource becomes limiting. This is pretty easy to model. Let's suppose that you drop in some frozen bacterial culture containing a concentration of 1 x 10^8 cells/mL. (By weight, that's mostly water, so you get ~1x10^11 bacteria to start- about 100 billion). Assume they double every hour under optimal conditions, and that the maximum concentration that the oceans can support is the same that you started with.
Okay, so the oceans of the world have a volume of about 1.3 billion cubic kilometres, or 1.3 × 10^24 mL. So how long does it take your cells to grow to fill that much water at their original concentration?
Well you start with 1x10^8 cells in 1.3x10^24 mL of water, for a concentration of 7.69x10-17 cells/mL. After one hour, you've doubled your number, so you have have 1.54x10-16. After two hours, you double again and get 3.08x10-16, etc.
Thanks to the ridiculous properties of exponential growth, it only takes 135 hours to reach your initial concentration, or about 5.4 days.
Obviously, this makes all sorts of unrealistic assumptions about optimal resource availability and the ability of wind and currents to mix the water so that the bacteria can spread. On the other hand, using the entire volume of the oceans is a large overestimate, because the top few meters get most of the sunlight and are the most hospitable to life.
So back of the envelope, I don't think an estimate of a month or two to colonize the world's oceans is all that unrealistic, if nutrient availability is as perfect as you descrive.
posted by chrisamiller at 6:33 PM on January 15, 2010 [2 favorites]
b) Once you drop them into the ocean, they're out of your control. Thus, there's no guarantee that the evolutionary pathways followed by Earth's early inhabitants will be similar there (in fact, it may be rather unlikely). You can stack the deck, but a few mutations and a slight competitive advantage may be all it takes to swing the entire ecosystem into producing massive quantities of methane and CO2, instead of oxygen. A few million years of that, and you end up with Venus, not Earth.
c) Along a similar note, due to the small size of the seeded population, I imagine that you're as likely not to hit an extinction event which wipes out everything. Imagine a simple system, where one species photosynthesizes and the other eats them. If the predators gain even a slight growth advantage, they'll quickly wipe out the base of the food chain, and consequently starve to death.
d) assuming that none of these things are problems, and that growth conditions are ideal, your population will enter an exponential growth phase until some resource becomes limiting. This is pretty easy to model. Let's suppose that you drop in some frozen bacterial culture containing a concentration of 1 x 10^8 cells/mL. (By weight, that's mostly water, so you get ~1x10^11 bacteria to start- about 100 billion). Assume they double every hour under optimal conditions, and that the maximum concentration that the oceans can support is the same that you started with.
Okay, so the oceans of the world have a volume of about 1.3 billion cubic kilometres, or 1.3 × 10^24 mL. So how long does it take your cells to grow to fill that much water at their original concentration?
Well you start with 1x10^8 cells in 1.3x10^24 mL of water, for a concentration of 7.69x10-17 cells/mL. After one hour, you've doubled your number, so you have have 1.54x10-16. After two hours, you double again and get 3.08x10-16, etc.
Thanks to the ridiculous properties of exponential growth, it only takes 135 hours to reach your initial concentration, or about 5.4 days.
Obviously, this makes all sorts of unrealistic assumptions about optimal resource availability and the ability of wind and currents to mix the water so that the bacteria can spread. On the other hand, using the entire volume of the oceans is a large overestimate, because the top few meters get most of the sunlight and are the most hospitable to life.
So back of the envelope, I don't think an estimate of a month or two to colonize the world's oceans is all that unrealistic, if nutrient availability is as perfect as you descrive.
posted by chrisamiller at 6:33 PM on January 15, 2010 [2 favorites]
Assuming you've waited long enough for the seas to fill up with microscopic life, what do you send in the second probe?
What's your goal here? To recreate conditions on Earth as exactly as possible? Or just to make it habitable?
posted by chrisamiller at 6:37 PM on January 15, 2010
What's your goal here? To recreate conditions on Earth as exactly as possible? Or just to make it habitable?
posted by chrisamiller at 6:37 PM on January 15, 2010
how long would it take for a kilo of pure algae to colonize an entire oceanic system?
Algae have a doubling time measured in hours. Assume a day. Say there's 1 billion km3 of water on your planet. Every m3 has, say....I have no idea. A gram of algae? So that's 1 billion billion or 1e18 grams per km3 or 1e27 grams in all. Which is 1e24 kg. log2 of 1e24 is ~80.
Three months. Which is obviously ridiculously fast, mainly because I assumed it could keep doubling. But only the algae at the "edges" can actually double. But give it a couple decades and it should be good.
posted by DU at 6:43 PM on January 15, 2010
Algae have a doubling time measured in hours. Assume a day. Say there's 1 billion km3 of water on your planet. Every m3 has, say....I have no idea. A gram of algae? So that's 1 billion billion or 1e18 grams per km3 or 1e27 grams in all. Which is 1e24 kg. log2 of 1e24 is ~80.
Three months. Which is obviously ridiculously fast, mainly because I assumed it could keep doubling. But only the algae at the "edges" can actually double. But give it a couple decades and it should be good.
posted by DU at 6:43 PM on January 15, 2010
One thing we could do today: Send up a nuke-powered heater to titan. There are already places on earth where there a closed-off ecosystems powered by closed-off nuclear material. If your nuke could give off enough energy to melt a (water) lake you would have an ecosystem growing right away.
Probably never enough to put up a thick enough greenhouse effect, though. But it would be cool.
posted by delmoi at 6:52 PM on January 15, 2010
Probably never enough to put up a thick enough greenhouse effect, though. But it would be cool.
posted by delmoi at 6:52 PM on January 15, 2010
Oh, wow Ganymed has a (very thin) oxygen atmosphere, and saltwater oceans, albeit burred under kilometers of rock.
posted by delmoi at 6:58 PM on January 15, 2010
posted by delmoi at 6:58 PM on January 15, 2010
Ok, here's an order of magnitude attempt:
This article suggests that a good approximation of population growth for phytoplankton is a doubling every 24 hrs.
Let's assume for simplicity that this space probe sprinkles its phytocargo evenly around the ocean, so we don't have to worry about interplankton competition for space or nutrients until we reach the maximum carrying density.
I found this random report (pdf) that suggests 10^6 cells/m^3 is a reasonable density for phytoplankton.
The article on the "photic zone" in Wikipedia indicates that in the ocean, phytoplankton can survive up to a depth of around 200 meters.
Ok. Now on a pseudoearth of the same radius and ocean coverage, that gives us 7*10^16 m^3 of photic zone. If we assume some kind of linear dropoff in phytoplankton density with depth, we can assume that the final number of phytoplankton will be:
3 * 10^22 phytoplankton
1 kg of phytoplankton would contain roughly 10^13 cells. Therefore, to get to 10^22, you need to perform roughly 31 doublings.
By that estimate, you'd need 4-5 weeks to fill the ocean with phytoplankton.
UNFORTUNATELY, this assumes the ocean is already saturated with oxygen, and there's no earthly or unearthly reason for the ocean to be saturated with oxygen unless there is already life there.
I'd expect they'd probably die off. Nice try though. Maybe if you got some of those anaerobic archaea seeded first, you could get some oxygen going.
posted by Salvor Hardin at 7:35 PM on January 15, 2010
This article suggests that a good approximation of population growth for phytoplankton is a doubling every 24 hrs.
Let's assume for simplicity that this space probe sprinkles its phytocargo evenly around the ocean, so we don't have to worry about interplankton competition for space or nutrients until we reach the maximum carrying density.
I found this random report (pdf) that suggests 10^6 cells/m^3 is a reasonable density for phytoplankton.
The article on the "photic zone" in Wikipedia indicates that in the ocean, phytoplankton can survive up to a depth of around 200 meters.
Ok. Now on a pseudoearth of the same radius and ocean coverage, that gives us 7*10^16 m^3 of photic zone. If we assume some kind of linear dropoff in phytoplankton density with depth, we can assume that the final number of phytoplankton will be:
3 * 10^22 phytoplankton
1 kg of phytoplankton would contain roughly 10^13 cells. Therefore, to get to 10^22, you need to perform roughly 31 doublings.
By that estimate, you'd need 4-5 weeks to fill the ocean with phytoplankton.
UNFORTUNATELY, this assumes the ocean is already saturated with oxygen, and there's no earthly or unearthly reason for the ocean to be saturated with oxygen unless there is already life there.
I'd expect they'd probably die off. Nice try though. Maybe if you got some of those anaerobic archaea seeded first, you could get some oxygen going.
posted by Salvor Hardin at 7:35 PM on January 15, 2010
Should have prefaced that with IANABiologist, so I have very little idea what I'm talking about.
posted by Salvor Hardin at 7:35 PM on January 15, 2010
posted by Salvor Hardin at 7:35 PM on January 15, 2010
delmoi: thanks for reminding me - I guess there are some unearthly reasons for some free oxygen, like solar wind splitting water in the upper atmosphere.
posted by Salvor Hardin at 7:37 PM on January 15, 2010
posted by Salvor Hardin at 7:37 PM on January 15, 2010
Chrisamiller's equations above seem more accurate to me even though he's leaving out factors like self-limiting waste byproducts and ... nighttime. The oceans on this planet would also have to be completely continuous, isolated bodies of water wouldn't be colonized.
You might find some of the links here interesting, some are more sci-fi than others.
posted by Locobot at 7:44 PM on January 15, 2010
You might find some of the links here interesting, some are more sci-fi than others.
posted by Locobot at 7:44 PM on January 15, 2010
Assuming the conditions appear perfect for earth-like life, and there is none, I imagine that whatever unseen force kept life from establishing itself on that planet would probably kill off whatever life you try to introduce.
You don't have sufficient data to say with what frequency life appears on Earth like planets, and thus to draw this conclusion.
posted by biffa at 3:12 AM on January 16, 2010
You don't have sufficient data to say with what frequency life appears on Earth like planets, and thus to draw this conclusion.
posted by biffa at 3:12 AM on January 16, 2010
Best answer: Two things:
1. I don't think plankton would last very long without a couple billion years' worth of preparation by prokaryotic life (e.g. bacteria), as others have said.
2. I think that on a planet "identical in climate and material composition to Earth," life would be either inevitable or impossible. Not possible but absent.
You have to have bacteria or extremophiles leading the way, in which case life has arisen, or else the plankton you send won't survive.
Good reading: Rare Earth by Ward and Brownlee.
posted by mcwetboy at 9:27 AM on January 16, 2010
1. I don't think plankton would last very long without a couple billion years' worth of preparation by prokaryotic life (e.g. bacteria), as others have said.
2. I think that on a planet "identical in climate and material composition to Earth," life would be either inevitable or impossible. Not possible but absent.
You have to have bacteria or extremophiles leading the way, in which case life has arisen, or else the plankton you send won't survive.
Good reading: Rare Earth by Ward and Brownlee.
posted by mcwetboy at 9:27 AM on January 16, 2010
Response by poster: Thank you, everyone; this is exactly the kind of discussion I was hoping for.
posted by Mars Saxman at 7:45 PM on January 16, 2010
posted by Mars Saxman at 7:45 PM on January 16, 2010
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posted by mr_roboto at 5:47 PM on January 15, 2010 [1 favorite]