the "machines" of a distant life form. After all, if you're about 3.5 miles up, life on Earth resembles an anthill. If time and size were perceived slightly differently by them, almost an inevitabilitie, they could have sent us to prepare Earth.

So, patiently waiting for us to warm it up a bit, maybe spread some radioactivity around, get the CO2 levels to where it would support their life, and then, like the Christian Rapture which they would have planted in our mythology, come back to claim a spot in the Universe which is finally able to support life, alien style.

Apocolypse then, so to speak.

Arf