About two years ago I posted about some very deep structures in the Earth near the core; a few years before that, I posted about an “Atlas of the Underworld” showing a bunch of subducted former continents. There is a new theory about those deeper structures: they are remnants of Theia, the Mars-sized planet that plowed into Earth  billions of years ago and shot out the rubble that became the Moon.

Why are there continent-sized ‘blobs’ in the deep Earth?

I suggested the faint possibility that hundreds of millions of years ago some Terrestrial species evolved to intelligence, built themselves a civilization and then got wiped out, their continent then being subducted. A hundred kilometers down there may be the superheated remnants of some ancient civilization. We will almost certainly never be able to go there to pick through the molten or semi-molten rubble… but if they built big enough, and out of the right materials (say, they made *vast* stone pyramids in regular grid patterns) it might just barely be possible that someday advanced tomography of the interior of the planet may detect signs of that civilization. An alien civilization mere kilometers away… and more difficult to get to than the forest world circling Alpha Centauri.

Well… who knows how far things got on Theia before it smacked into Earth. It might have been the seat of a galactic empire. The whole surface of the planet might have been covered with a ten-mile-thick solid city structure and equipped with several levels of orbital rings. And then it hit Earth. A thousand kilometers down, laughably far away, may still reside some of the tougher megastructures built out of heat resistant alloys that mankind hasn’t even come to dream of yet.

Likely? No. Possible? Maybe. An intriguing enough idea that paramount should promptly stop funding STD and STP to instead start work on a series about this ancient civilization? Yes.