First for a clarification: Eric Drexler never proposed molecular assemblers in serious (i.e. he has not worked out and published technical details on them). Mol

First for a clarification: Eric Drexler never proposed molecular assemblers in serious (i.e. he has not worked out and published technical details on them). Molecular assemblers have been just a self suggesting early analogy in his first popular science book. What he did later in serious actually proposed (in his technical book "Nanosystems") was macroscopic sizes nanofactories with nanoscopic nanomechanics inside as a sensible far-term-target falling out of exploratory engineering methodology. These nanofactories have not failed. They could not yet been tried due to the underlying technologies that eventually lead there having not yet been developed and ready. Waht is the case is that people repeatedly massively underestimate the immense multifaceted difficulty of eventually getting there. These technologies including mainly: – self-assembly technologies beyond nature (incremental via foldamers path) – early primitive mechanosynthesis (direct to gemstones path) To the actual question here: As for why we don't use microorganisms (or algae) more for carbon sequestration. I guess packaging and protecting them to keep them alive is very costly. More packaging needed than solar panels due to (~10x?) lower efficiency. Same reason we do most of our farming still outdoors not in expensive but against hail and wind protecting and growth rate boosting hard glass roof greenhouses or even nicely pest compartmentalizing and massively land area saving vertical farming. Nanofactories (and machines made by them) could make building say algae-panels >99% cheaper eventually. Though as mentioned it will take a long time till we have these devices. Even with dedicated efforts which we currently do not yet have enough of. In the meantime till we have such amazing technologies we have to look for other solutions that work. No packaging needed fertilizing the sea with iron I find to be scary geoengineering. Makes me worried about anoxic dead zones if overdone. Messing with the ecosystems we'll likely kill even more species by bringing it out of balance making the algae population deliberately explode. Classic non-biological methods not messing with the ecosystem like solar panels seem to work well. But storage is needed too. Yes not carbon sequestration here, but for storage green hydrogen seems good if it could be made just a bit more efficient in conversion. Nicely seasonable storeable for the "dunkelflaute" in former natural gas reservoirs. I don't buy that "we can't do that because embrittlememt of gas pipes" argument and the "funding green hydrogen funding natural gas" argument.