There was no easy explanation for it, no science to identify why it happened. Even the religious zealots were at a loss to explain it, at least at first. They quickly scrambled to say that their god had provided us with indefinite existence, and surely they were a powerful and loving god. Many people were eager to believe this, for no one else had anything better to say. Still many didn't, though they acknowledged the miraculous nature of the occurence.
What happened? The world was going to end. People were rioting in the streets, world leaders had all but vanished. Our natural resources were nearly depleted. Deforesting, mining, oil drilling, had all left us without anything. We'd bled the Earth dry. Our ozone layer was shredded, and everyone were ultimately bound indoors, for fear of the radiation and lack of protection from the UV waves. Sickness was rampant, hunger even more so. Humanity was staring down the barrel of its own hubris.
Lo and behold, we were saved. On April 9th, 2099, a colossal hole in the fabric of space and time tore open in our solar system. To us here, it appeared as a flash of light, and a rumble louder than any thunder ever heard. Where the sun would have shined in the sky there was now a spacial mirror, reflecting our planetary visage back to us. Showing us the failures we had made in our strides toward "progress".
Yet... it was an inverse reflection. A negative image of what our world is. There were lush greens and deep, blue oceans. Somehow the same and yet not. Where we had continents, this world though the hole in space had their oceans. Our oceans mimicked their continents. There was mass hysteria and confusion, and people began to shout for guidance. The religious leaders were first to answer the call, loudly and publicly. They made claims about the authenticity of their various gods, and how this was a literal celestial sign.
Meanwhile, the men and women of science were already in motion to send expeditionary missions to the new world. They knew that they had to assemble every last resource to make a hail mary pass for the salvation of our species. NASA led the charge, collecting together the best and brightest astronauts from all over the world. The only non-astronaut member of this new crew was a cartographer named Elise Clarc. She would be responsible for mapping this new world.