I believe the "aliens" probably live under our oceans. Possibly an advanced civilization that has lived on Earth for many many millenniums, if not longer.

Even perhaps not aliens at all, but terrestrial to this planet. Who's to say that during our 4+ billion year history another civilization hasn't existed with tecnology that dwarfs our own.

When you think about it, our written history only goes back a few thousand years out of 4+ billion. We're barely a sentence in a book containing a million of pages.

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