But there is enough Uranium and Thorium for many centuries, even millennia.
The most important problem to solve is climate change; besides aging as the most important reason for misery and death today.
But the replacement of animal products by vegan food is the only sane choice for medical, ethical, economic and ecological reasons.
http://www.whatthehealthfilm.com/
https://www.youtube.com/channel/UCGJq0eQZoFSwgcqgxIE9MHw/vid...
https://www.youtube.com/channel/UCJRjK20fHylJyf-HiBtqI2w/vid...
A big problem with Mars is that getting fuel there is expensive, they sometimes have large dust storms, and their atmosphere is very thin. Solar power would work fine there 90+% of the time, but outside of fission, there doesn't seem to be any good technology for powering a human habitat over long periods. A rich thorium deposit on Mars could go a long way in creating a self-sustainable habitat. Some thorium reactor designs are notable for their high inherent safety, which is probably a big concern for any human habitat on Mars for morale reasons (think about how much a fatal nuclear disaster on a Martian colony would scare people about space exploration)
But going to Mars in the next decades is a useless horrific suicide mission that only serves to make a few people famous.
IMO persons will colonize moons, planets and space ships once their biological body is replaced by a machine body. In a biological sense, the human race will die on Earth.