Nuclear reactions power the stars, and rather importantly, our Sun. The Sun provides warmth and weather. The Earth's molten core is still molten thanks to nuclear decay, and as such we get plate tectonics and volcanism (which are responsible for most of our atmosphere) and a magnetic field (which protects the Earth's surface from the bulk of cosmic radiation, and gives us the auroras). And nuclear fission can provide us with clean electricity to continue powering our society. It's all thanks to nuclear physics!
It would appear I get the dubious honor (notoriety, perhaps?) of having my recent interview published on Earth Day, so I wanted to leave you with an Earth Day sentiment.
"In a city, everything is available all the time. Meat comes in plastic wrap and nobody thinks about the steer it came from. Death and birth are going on all the time, and you witness that when you're living on the land. But in cities and suburbs, that's all hidden or ignored.... People want goods and services and energy but they don't want to think about the costs to the environment. This is why I'm so scared of global warming. Almost nothing is being done." - Dr. R. Anderson (Sandia Nat'l Lab, quoted in Gwyneth Cravens' Power to Save the World)