Turning CO₂ into Diamonds

Really Wild Stuff

No, I don't know how to turn CO₂ into diamonds. Presume millions of skilled people devote decades to developing precisely specified, precisely controlled (with multiple well-tested failsafes) pseudo-biotechnology. I'll call the biodevices "bugs", microbe-scale but with a completely different biochemical plan.

• What might that be? If we want perfect control, Darwinian evolution is the enemy; the bugs might evolve to be better reproducers and escape our control. Our task is to make bugs that cannot replicate without external help, supplied by a network of other bugs similarly constrained. A bug with a failed checksum stops working, is evaluated, and marked for recycling by other bugs.

We test the bugs out of the gravity well, perhaps in a Russian doll series of vacuum and acid bottles, sealed in a cave on the Moon. We are testing microbes, so the apparatus can be small. Presume we make absolutely sure we get it right before we release them anywhere.

Let's presume the network of bugs is constrained by an artificial "nutrient" supply, perhaps a molecule that enables 1024 bug operations, then stop until another molecule is received. We deposit the bugs in low productivity regions of the ocean, perhaps 1.7% of the total ocean, 1% of the Earth's total surface (0.01*4π*6378*6357 km² = 5.1e12 m²), 1% of the Earth's sea level insolation. Presume the bugs can convert CO₂ to O₂ gas and elemental carbon, which is formed into diamonds by groups of other bugs, with 5% energy efficiency (P.O.M.A.).

The enthalpy of formation of CO₂ is 393.52 kJ/mole, and CO₂ is 0.044 kg per mole. At 5% efficiency, that is about 1.8e8 J/kg. Average surface insolation is 250 W/m², so one square meter produces 7.9e9 J/year, consuming 44 kg of CO₂ and producing 12 kg of diamond per square meter. Globally, that is 2.2e14 kg of CO₂ consumed, 6e13 kg of diamond created per year.

The atmosphere weighs 5.5e18 kg. 1 ppm of that is 5.5e12 kg. Our system of bugs can draw down CO₂ by 40 ppm per year. In eight years, we can go from 600 ppm to 280 ppm atmospheric CO₂, then stop enabling the bugs, then scavenge them for other uses, leaving a crust of diamonds about 3 centimeters thick on the floor of the deep ocean. Or, we might find a few other uses for 480 billion tons of structured carbon; perhaps 100 million Burj Kalifa-scale skyscrapers, 30 million square kilometers of floorspace, 3000 square meters for each of 10 billion people. Aren't stupid-big numbers fun?

• 6 H₂O + 6 CO₂ + 2805 kJ → 6 O₂ + C₆H₁₂O₆

  • 6 CO₂ + 2361 kJ → 6 O₂ + 6 C

The latter is energetically cheaper, but biologically unlikely. Photosynthesis normally makes hydrogens, which combine with CO₂ to make CH₂O subunits and ½O₂:

• 6 H₂O → 12 H + 3 O₂

• 12 H + 6 C O₂ → C₆H₁₂O₆ + 3 O₂

So to directly make only carbon and oxygen gas will require a completely different synthesis pathway.