Renewable Energy vs. Nonrenewable Energy

     Nonrenewable energy resources include nuclear, hydrogen, coal, natural gas, and oil. All of these currently fail the definition of sustainability in one way or another but most painfully in the ability of the environment to absorb and regenerate the expenses related to their extraction or production. 

   One of the best-known examples of green technology is the solar cell, which directly converts energy from natural light into electrical energy via the process of photovoltaics. Generating electricity from solar energy equates to less consumption of fossil fuels, as well as the reduction of pollution and greenhouse gas emissions.

   Other renewable energy sources include hydro, biomass, wind, and geothermal, but unfortunately, these assets are not currently be exploited at adequate levels to replace nonrenewable sources. The bottom line is that while non-renewable energy resources currently comprise 80 percent of the world's energy requirements, over time, that's simply not going to sustainable. If we hope to maintain life on our planet, emerging green energy technology must be used alongside existing methods to transition from the unsustainable to the sustainable.

Which of the following resources isn't a renewable resource?