Oxygenating a 'primordial' atmosphere...

[Nik_2213]

Imagine a generic terrestrial planet in potentially hab zone around a generic mid-K star. No life as yet, carbon dioxide about 15% of atmosphere and nitrogen 75%, so significant 'greenhouse' effect. Mild tectonic cycle. Cool enough for hydrological cycle: Clouds, rain, rivers, seas, lakes etc. But, ~ 5 Bar.

Life on Earth took a long time to get started, switch to oxygenation, knock down the iron-laden seas.

Our current photo-synthetic micro-organisms, honed by billions of years of evolution, should do much better...

If an appropriate mix of types could be 'seeded' into many upland lakes so they are steadily fed into water-courses, colonising the back-waters then shallows, estuaries and coasts, dispersing across the seas...

As I understand it, their spread is only limited by lack of nutrients, so multiple local cycles of 'Bloom & Bust'...

There's a lot of atmospheric CO2, but sea water is too warm to hold enough to 'buffer' its loss.

As the atmospheric CO2 diminishes, and dissolved iron precipitates due to oxygen generation, you get down to ~ 4 Bar 'mostly nitrogen' long before any free oxygen makes it into the atmosphere. Puncturing the 'greenhouse' also cools and shrinks the atmosphere, perhaps by another ¼~~½ Bar...

Any ideas for how long these stages would take, from initial seeding ??

Yes, yes, longer than a 'standard' life-time, but this would be in the 'next system over', like newly-weds planting pips for their grown children's orchard, acorns for grand-children's oaks...

 

[stefan r]

The easiest and fastest way to sequester carbon dioxide is going to be asteroidal magnesium and other alkali or alkaline earth elements. If you want cheap sloppy fast you can crash olivine and burn it on reentry.

In my opinion more sophisticated colonists will fashion magnesium alloy frames for telescope lenses. Mirrors and lens can be utilized for as the large part of Dyson sphere when it is not being used to focus on research. Magnesium alloy is competitive with iron steel in applications that call for rigidity. The tensile strength looks misleadingly weak because the density is much lower.

The energy limits of separating an atmosphere can be calculated from the gas law. The lower the concentration the more difficult it becomes. The partial pressie of CO2 at start is 0.75 bar. Because of this i would suggest starting on the surface and using the space resources in space for a few generations.

The crust on Earth turns over by itself. Thankfully that happens relatively slowly. The basics of sea floor spreading and subduction can be boosted a great deal. On Earth the weight of the Pacific ocean is helping to shove the Pacific plate down under Asia. Lifting material from the mid Atlantic ridge to the east Pacific is not even an elevation gain. Also on Earth salt water sinks in the Arctic ocean and then eventually surfaces in the Pacific upwelling. Carbon dioxide is heavier the water. Sinking it in the polar regions will be a net energy gain. Formic acid, nitric acid, and carbonic acid are all denser than water. Ethanol also sinks. Acids are a great way to destroy terrestrial rocks. There is not need for completely dissolving rocks in the rift zones. Just etch some parts loose. Mostly still intact boulders can be lifted and floated away.

0.75 bar CO2 is about 2 tons of carbon per square meter. A space faring civilization should just build a vast city with graphene and diamond structure.

If you like bio that is fine too. Think "what would beavers do". Except that beavers and trees are often working at cross purposes. An engineered plant should be able to just grow the roots into streams. Some trees and plants (willows, reeds, cattails, bulrush) have air tubes in their roots. Plants could greatly vary their density distribution. They could hydrate the above ground stalk and leaves like a succulent or cactus. Likewise they can deflate the under water air tubes. Then they can reverse and transpirate all the water while making the roots buoyant. This inflation process could also adjust the horizontal pressure that roots place on each other. Nothing like this has evolved on Earth since such a forest would rapidly its own habitat. There is no need for simple but a simple regulation mechanism could follow a moon. The tide would give the flood cycle extra leverage.

On the ocean side use reef builders like coral

On Earth we had a fairly rapid carbon sequestration during the Azolla event. The species looks like modern azolla but is not exactly the same. It was able to create a fresh water lens above the Arctic ocean. Then it would die each year because of the lack of sunlight in arctic winter.

In all these cases the hydrologic cycle can be leveraged. Have long rows parallel to the prevailing winds. Rapid transpiration can create saturated humid air which should rise. The wind can follow a corkscrew pattern and pick up much more water than it would otherwise. A few tons per square meter is not that much.

 

[phinds]

A few tons per square meter is not that much.

Huh? FIrst off, square meter has no thickness so holds zero. Secondly, tons per cubic meter? Really? Per cubic kilometer, sure.

 

[stefan r]

Huh? FIrst off, square meter has no thickness so holds zero. Secondly, tons per cubic meter? Really? Per cubic kilometer, sure.

A planet's surface is a surface. It has square meters.

Things sitting on the surface have mass. So tons. Tons per square meter.

We could use PSI but we need to know the gravity. That and i prefer metric.

 

[Rive]

Our current photo-synthetic micro-organisms, honed by billions of years of evolution, should do much better...

Tricky. Those millions of years were spent in an environment with both oxygen and CO2 freely available.
Plants suffocate in a pure CO2 atmosphere - at least as far as I understand.
I don't know if common aerobic microbes (algae?) could do better.