Page "Molecular nanotechnology" Paragraph 22

A fear exists that nanomechanical robots, if achieved, and if designed to self-replicate using naturally occurring materials ( a difficult task ), could consume the entire planet in their hunger for raw materials, or simply crowd out natural life, out-competing it for energy ( as happened historically when blue-green algae appeared and outcompeted earlier life forms ).

Some commentators have referred to this situation as the " grey goo " or " ecophagy " scenario.

K. Eric Drexler considers an accidental " grey goo " scenario extremely unlikely and says so in later editions of Engines of Creation.