Living creatures—including humans—would be the primary victims of an exponentially spreading nanobot attack. The principal designs for nanobot construction use carbon as a primary building block. Because of carbon’s unique ability to form four-way bonds, it is an ideal building block for molecular assemblies. Because biology has made the same use of carbon, pathological nanobots would find the Earth’s biomass an ideal source of this primary ingredient.
How long would it take an out-of-control replicating nanobot to destroy the Earth’s biomass? The biomass has on the order of 1045 carbon atoms. A reasonable estimate of the number of carbon atoms in a single replicating nanobot is about 106. (Note that this analysis is not very sensitive to the accuracy of these figures, only to the approximate order of magnitude.) This malevolent nanobot would need to create on the order of 1034 copies of itself to replace the biomass, which could be accomplished with 113 replications (each of which would potentially double the destroyed biomass). Rob Freitas has estimated a minimum replication time of approximately 100 seconds, so 113 replication cycles would require about three hours.2 However, the actual rate of destruction would be slower because biomass is not “efficiently” laid out. The limiting factor would be the actual movement of the front of destruction. Nanobots cannot travel very quickly because of their small size. It’s likely to take weeks for such a destructive process to circle the globe.
Nanotechnology Dangers and Defenses | KurzweilAI