Energy exists freely in nature. Some of them exist infinitely (never run out, called RENEWABLE), the rest have finite amounts (they took millions of years to form, and will run out one day, called NON-RENEWABLE). Non-renewable energy is energy from fossil fuels (coal, crude oil, natural gas) and uranium.Fossil fuels are mainly made up of Carbon. It is believed that fossil fuels were formed over 300 million years ago, when the earth was a lot different in its landscape.It had swampy forests and very shallow seas.nergy exists freely in nature. Some of them exist infinitely (never run out, called RENEWABLE), the rest have finite amounts (they took millions of years to form, and will run out one day, called NON-RENEWABLE). Non-renewable energy is energy from fossil fuels (coal, crude oil, natural gas) and uranium.