[rad88]

Long-term we could plant massive new floating plant species in the atmosphere to decarbonize it and form floating soil layers, which eventually would compactify and metamorphosize and spread out latitudinally to form a ring around the planet, thinning out towards the poles and making cliffs and beaches and islands with the atmosphere. The growing regions would not actually stay together but break apart and move technically on top of the atmosphere, with plate boundaries and subduction zones and volcanoes, driven by the pressure below, surface volcanism proper, and weather around the coastal areas.

[pencilguin]

Keeping carbon persistently out of the atmosphere would be hard, if you are freeing oxygen.

One alternative would be to make diamonds out of the extracted carbon and drop them to the ground. The released oxygen could then bind to crustal aluminum, iron, silicon, calcium, etc.

Venus has sadly little hydrogen, so you won't get oceans.

[credit_guy]

Just for a sense of scale, the venusian atmosphere has a mass of about half a billion GigaTons, 97% of which is CO2. Here on Earth, with all our industrial infrastructure, the substances we produce the most (iron and concrete) are in the low single digits GigaTons per year. The next ones (fertilizers and plastics) are in the hundreds of megatons per year. If you want to make a difference on Venus, you'd need to make millions of time more diamonds each year in some balloons in the skies than we make iron here on Earth.

[pencilguin]

It is a matter of how big a hurry you are in.

But, yes, it would be pointless to try terraforming Venus without von Neumann machines, and then it would end up thick with those, instead.

The Kuiper Belt offers more than the inner planets, provided energy is solved e.g. via aneutronic fusion.

[credit_guy]

> provided energy is solved e.g. via aneutronic fusion

You can use regular fission as a dense energy source. If you are worried about the waste, you can just blow it up. In space there's no fallout. The particles from the explosion will just move radially forever. Most of them (99.9999..%, too many nines to count) will keep moving for billions of years through empty space without encountering anything. Oh, and as a curiosity, if you blow up a nuke in space, there's no fireball. The fireball we see in movies of nuke detonations are due to the air absorbing the X-rays from the nuke and becoming overheated plasma. But there's no air in space, so a nuke explosion is invisible and silent.

[pencilguin]

Fission is not a good energy solution for the outer solar system (except maybe on Titan) because of the need for a detour through a clunky heat engine. Likewise, hot-neutron fusion.

Layered mirrors concentrating monochromatic solar irradiation into laser cavities, and beaming power to where needed, is the fallback until aneutronic fusion works.

[rad88]

Might the lighter O2 naturally rise away from the organics layer? It may then be able to oxidize metals and meteors sprayed into the upper atmosphere, eventually falling back down with those compounds to fertilize the substrate.

[pencilguin]

Wind speed is hundreds of km/h. So, "turbulent mixing processes" rule.

There is plenty of un-oxidized material on the ground. Oxygen just needs to be kept off the carbon. And, it needs stirring. Big meteors could do a bit of that.

Earth gets its stirring from tectonics, which Venus lacks.

[zeristor]

Just to chip in, that life on Earth produced oxygen from photosynthesis, which over billions of years oxidised the iron in the ocean producing the iron ore beds as it precipitated out.

This occurred in stages.

[pencilguin]

To work, it needed stirring from plate tectonics.