For 4.5 billion years, life evolved on planet Earth.  Not once were the inhabitants of this tiny blue mote of dust able to gaze upon their home as one entity.  To them it had always been an endless land without borders and an endless supply of food and resources.  Most of them were blissfully unaware that they could ever venture further, and so they accepted the boundaries of their existence unquestionably.  Once humans started making tools, we were taken down a path of discovery that would let us escape the bounds of our shrinking world. Finally, just over 70 years...