In the 1970 Doctor Who serial Inferno, what alternate-world project threatens to destroy Earth?

In the 1970 Doctor Who serial Inferno, the alternate-world threat is the Inferno drilling project.

The serial stars Jon Pertwee as the Third Doctor and takes place around a massive drilling operation intended to reach a powerful energy source beneath Earth’s crust. In the parallel version of events, the project has advanced dangerously, producing catastrophic consequences for the planet.

The serial is notable for its alternate-universe setting. The Doctor becomes separated from the TARDIS and discovers a world in which familiar characters occupy altered roles and the drilling project has not been stopped. The story uses the Pandora myth as a thematic reference to the release of destructive forces.

The project’s name is often confused with the serial’s title or with unrelated fictional drilling operations. Its canonical name is the Inferno project, making “Inferno drilling project” the specific answer.