Nonrenewable resources like coal, petroleum and natural gas cannot be replenished in a short period of time and will eventually run out. They were formed from ancient organisms millions of years ago. Renewable resources such as solar, wind, water and biomass can be naturally replenished in a short period of time through natural processes and are less finite than nonrenewable resources. The key difference between the two is whether the resource can be naturally replenished within human timescales.