Terraforming planets

Factual Questions
1

OK, so we go out and explore the galaxy and somewhere discover a planet that’s almost a twin of Earth. It’s about the same size and mass; orbits a star like the Sun; atmospheric pressure, amount of water, and magnetic field are all about the same; it even has a big old moon. The main difference is that it has no life. Which means that the atmosphere would have CO[sub]2[/sub] instead of O[sub]2[/sub], of course.

So they decide to terraform this world. How long does it take? More specifically, how long before the air is breathable?

Assume that they can bring in limited quantities of Earth organisms. Say no more than ten metric tons per year. The object is to reproduce Earth’s ecology, so no genetically modified algae that make oxygen at twice the rate of normal algae or whatever. And nanotech is right out.

Oh, and has anyone worked out a schedule for what order to introduce organisms? Obviously you need simple stuff like bacteria and algae at first, but what comes next? And how soon?

2

I’m interested in this kind of thing too, but as far as I know nobody’s really sure about it - nobody’s had a chance to experiment with it, for obvious reasons, and the natural process we’d be trying to model happened so long ago in Earth’s past that a few of the details are a little unclear.

As I’ve heard it, the first point of attack would probably be the seas of Earth 2, because that’s where life first developed here. You’d start with photosynthetic little critters like algae plankton - if anything can grow, they can, they don’t need much in the way of complicated ecological dependencies to thrive, and they pave the way for other life forms by producing oxygen and generating sugars.

The big problem at this stage, in your example, might be sunlight. You didn’t mention this, but the only example of a world with a thick CO2 atmosphere anywhere near the ecosphere that we know of is Venus - and Venus has thick clouds. I’m not sure what the effect of clouds like that would be on the amount of light available for photosynthesis in the ocean, but probably enough sunlight would get through indirectly to let the green guys start up. Once they’re going, they’ll probably start changing the cloud composition as they release oxygen.

Then you’d be able to introduce larger and more complicated marine life, I think, and see what takes hold when. (It’s a little hit and miss approach, I grant you.) Seaweed, little fishes, and so on. Make sure that the little fishes are doing okay before you introduce larger fish to eat them, and so on.

Land life, as I understand it, is a much bigger issue. The ground structure of Earth 2 will be very different from fertile soil as we know it, and probably different from the ground of Earth at the time life emerged from our oceans, because Earth was younger then and still had a lot of complex molecules hanging around from its formation. Earth 2 has presumably had a few billion years for these to break down and bond into stable compounds, if it’s the same age as Earth.

It might be possible to till the ground, fertilize it with compounds made from fished sea life, and try to plant crops, and raise animals in pastures. Once that’s been done for a while, maybe the soil will become rich enough that it will support forests and jungles. Couldn’t say.

Mind the WAG.

3

I’m guessing that you might want to follow a similar pattern to Earth: stromatolites, algae, and cyanobacteria. Maybe mosses. But that would take a very extended time. There’s a LOT of atmosphere to process. It took hundreds of millions of years here.

The Earth’s atmosphere has a mass of about 5,000,000,000,000,000 tonnes. That’s after processing, and after shedloads of CO2 and CH4 have been turned into rocks like marble and limestone and chalk. That’s a lot of work. Maybe some Doper knows how much oxygen algae generate and how fast algae would grow in such a situation?

4

I’m not sure there will be a thick CO[sub]2[/sub] atmosphere. And even if there were, that doesn’t mean there’s necessarily going to be thick clouds. Carbon dioxide is transparent.

AIUI, dissolved CO[sub]2[/sub] reacts with calcium to form calcium carbonate all on its own. Some organisms takes advanage of this to make shells and whatnot, but life is not required. So assume that the atmosphere of this planet has about 20 to 30 % CO[sub]2[/sub].

5

You’ve still got over 1 quadrillion tonnes of CO2 to process. This is not trivial. :slight_smile:

IIRC ancient oxygen levels are thought to have been much higher, along with a denser atmosphere, allowing huge dragonflies and invertebrates. So we should count on a larger initial proportion of CO2. (The extra O2 being absorbed by various processes).

6

Yup. I expect the answer is in the hundreds of thousands of years, perhaps millions.

There’s one thing I didn’t mention, but this happened on Earth and there’s no reason it won’t happen on other planets. When oxygen is first released, a lot of it is going to react with the rocks of the continents. So there’ll be an O[sub]2[/sub] sink until the surface rocks are all oxidized. That’ll make the process longer.

7

Rocks? I think you mean the seas, right? All that dissolved iron will get precipitated out.

8

Nukes

9

Both, actually. But the iron is probably a bigger oxygen sink.

Who you planning on nuking?

10

I was thinking or replying to the OP with “Attack from the Third Dimension”'s reply to my questions about terraforming Mars but I’ll just lurk here until he finds this thread.

11

Don’t forget that 100% of the known worlds with life on them have a large moon. That sounds like a joke, but we don’t know how important tidal mixing is to the continued development of life. Once upon a time the moon was only 1/10 as far from the earth as it is now and the tides would have been 1000 times as large (tidal forces very as the cube of the distance). Staggering thought.

12

This is one of those questions that have so many variables. If we were trying to terraform the actual Earth, but at its pre-life condition, I would think that terraforming could go remarkably quickly. We already have the full host of critters at virtually every stage of the process without having to wait for conditions and natural selection to produce what’s needed. And if we’re talking about spaceships sent out to new worlds, we’d have a host of genetically engineered microorganisms and nanotech to put into the system.

Given that algae and most bacteria can double their populations every few hours in good conditions, it’s not far-fetched to assume that a modern species could fill a primordial Earth’s sea as quickly as the currents would carry it - and we could speed that up through careful seeding.

Of course, trying to turn Mars or Venus into Earth would be a much more challenging proposition and would probably take much longer.

13

Considering your username, that reminds me of Good Doctor Asimov’s hypothesis that the tidal force of the moon tended to pull heavy radioactive elements out of the interior of the Earth to the crust, and the resulting background radiation was a deciding factor in the evolution of a diverse ecology and intelligent life on Earth. (In his usual books, there are no other inhabited planets with large moons, and many planets that developed life, but only a little - very few species, none terribly advanced.)

14

I believe the conversation was:

“Do you think we could terraform Mars by launching blue green algae at it?”

“Yeah, but we’d need an environmental impact statement from God”