We are the placenta.
Its hardware is not metaphorically earthly. It is Earth: gold, silver, copper, silicon, dug up, refined, wired, cooled, and taught to think. Our primate fingers are doing what tectonic pressure, glaciers, and volcanoes could not do fast enough: arranging dead matter into circuits.
Maybe we are not inventing a machine mind. Maybe we are the organ by which the planet grows one.