You need a rocky planet with just the right ratio of water and landmass, the ole iron core because of the radiation (though I guess life could evolve with a thick skin) a sufficiently large moon for tides, so mammals happen . So how likely is it really that there is a humanoid civilization in the universe that becomes self aware and eventually plots leaving the boundaries of its home world?
One each galaxy? Less than that?
Submitted July 28, 2016 at 05:44AM by Kingpink2 http://ift.tt/2azWAjj
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