Mr. Marlow's book and interviews _GROSSLY_ overstate the maximum possible
rate that rogue nanobots can replicate. Based on extremely general physical
principles, such as the conservation of energy and the limits of available
energy vs. the characteristic energies of chemical bonds, Dr. Robert Frietas
has shown that the maximum possible "biomass to nanobot" conversion rate of
self-replicating nanobots cannot possibly be greatly larger than that of
already-existing self-replicating organic lifeforms such as bacteria, so
that far from "destroy[ing] the planet in a matter of days," the timescale
for complete "ecophagy" (conversion of the entire biosphere into nanobots)
is in fact quite long --- on the order of _TWO YEARS_, not two days.  
In particular, exponential growth of a nanite infestation cannot possibly be
sustained past the earliest, initial stage of the infestation, due to energy
and resource limitations, as well as production of waste heat by the nanobots;
hence, late growth can only occur at polynomial rather than exponential
rates, and at the surface of the expanding colony rather than throughout
its volume.  Therefore, the response time required to deal with a rogue
nanotech infestation will _NOT_ be on the order of "minutes" as Mr. Marlow
claims, but rather on the order of days or weeks --- i.e., comparable to
the response time currently required to deal with an epidemic outbreak of a
typical infectious disease.

Please see <http://www.foresight.org/NanoRev/Ecophagy.html> for
Dr. Frietas' complete analysis.

In short, Mr. Marlow has paid too much attention to the overblown and
scientifically inaccurate claims of doomsday science fiction writers
(many of whom are scientifically illiterate luddites), and too little
attention to the physical limitations imposed on _ALL_ forms of nanotech
by real-world physical laws.

-- Gordon D. Pusch  

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