While the ‘mechanosphere’ is a concept mentioned only six times in A Thousand Plateaus, it is fundamental to the way Deleuze and Guattari construct their geophilosophy. In this article, I argue that the mechanosphere solves what Louis Althusser calls the idealist coupling of mechanism and spiritualism implicit in Teilhard de Chardin's noosphere and in Jacques Monod's appropriation of the term. My contention is that the mechanosphere must be contextualised within Althusser's critique of Monod, delivered during the ‘Philosophy Course for Scientists’ at the École normale supérieure rue d'Ulm in 1967. Reading A Thousand Plateaus (1980) against Monod's Chance and Necessity (1970) and Althusser's Philosophy and the Spontaneous Philosophy of Scientists (1967), I argue that the mechanosphere evacuates the spectre of an ‘idealist tendency’ latent in Monod's molecular science. By refashioning Teilhard's Omega point, Deleuze and Guattari create a sphere that serves as an asymptote on the horizon of ecological history – a projected point of complete destratification between the production of human subjects and planetary ecology. Ultimately, the mechanosphere nuances contemporary treatments of the Anthropocene, asking us to consider not only how humanity is overwhelming natural forces, but also how the former category is becoming increasingly indistinguishable from the latter.