Duniverse in a nutshell (this is mostly based on the new prequels: Earth is barely mentioned in the original Dune books).
Some untold period of time after now, the Earth will be united under a decadent monarchy, the Old Empire, which controls a number of worlds. The culture has stagnated, the people relying on technology for all their needs. Then the visionary known as Tlaloc organised a group of 20 'Titans' (who sound suspiciously like typical Ah.com poster material
) and, by taking over the controlling computer network, overthrew the Old Empire.
The Time of Titans lasted a hundred years; Tlaloc died in a shuttle crash and, shocked by their own mortality, the remaining Titans transformed themselves into 'cymeks': human brains in jars which can control a variety of robotic bodies. However, the Titans were then themselves overthrown and reduced to mere captains when the computer network developed sentience as Omnius, the evermind. Omnius' empire, the 'Synchronised Worlds', was centred on Earth: like all Synchronised worlds, the human populace was then reduced to slavery to the thinking machines. Over the next ten thousand years' of Omnius' reign, Earth became largely covered with vaunted neo-classical architectural follies masterminded by the sidelined Titans.
However, a collection of out of the way worlds centred on Salusa Secundus formed the League of Nobles, a free(ish) counter-government. The ten thousand years featured intermittent war between Omnius and the Nobles. Then, focusing on the symbol of a human child being callously slaughtered by a robot on Earth, the Butlerian Jihad against all thinking machines raged across the galaxy. The humans rose up on Earth, but were all killed by Omnius' minions. Knowing that there were now humans left on Earth, the League then deployed a fleet which destroyed the planet's surface with nuclear weapons.
Presumably by the time of Dune, a further ten thousand years later, Earth is still a smoking atomic cinder. Notably, details of Earth history seem to be few and far between, although we are alerted that Dune 'hero' Paul Muad'Dib idolises Genghis Khan and 'Emperor Hitler'