Fissible materials are not a good long term solution, they create a lot of wastes and, like coal and oil, once it's gone, it's gone.
Technically, the same with fusion materials, at least in the near term where we have to gather it from either oceans or the moon.
THat's not the issue, it's hopping from a finite resource to a finite resource that is. We need to harness energy sources that we cannot deplete, but that implies starting to think about how we use energy and how to reduce these usages so the sun, wind, waves and planet temperature can be harvested.
The earth has enough energy surplus to sustain life, no reason we shouldn't be able to use that. And when it comes to mars, there is still the sun.
100,000 years is enough of a time to hop from a finite resource to a near infinite one if we use our time semi-wisely.
We can deplete geothermal in a few millennia.
The sun on the earth has a significant but diffuse energy that we would deplete our stores of other resources to make enough solar panels to harvest enough of. Maybe if they were space based...
Wind could only be harvested in sufficient amounts to sustain the world if we accept a massive swath of terrible environmental damage to mine the rare earths required for the magnets, and the wind turbines and blade systems have to be rebuilt every 20-45 years depending on size (Larger ones are showing to have significantly less usable life).
Tidal power is hard to near impossible to harness in most cases, and when it is it has massive environmental impact.
Hydroelectric power has probably the most ecological impact of all of these, and it's future is in doubt due to climate change.
Fusion would require a technological leap and will have neutron activation problems creating significant amounts of radioactive waste until we use He3.
Fission will always have waste problems, and if breeder or thorium reactors are not used the fuel supply would be significantly less.
However, out of all of these only fission and fusion can really be realistically looked at for the long term due to their energy densities and their significant reduction in raw materials to make a meaningful amount of power.
Ultra-long term. Orbital solar power collectors or fusion are the only real options for humanity at this stage in our near term development.