Renewable energy utilizes natural cycles and systems—such as sunlight, wind, tides, and geothermal heat—to create energy in a form ready for human consumption. These sources differ from fossil fuel, for example. Probably one of the oldest usages of renewable energy is harnessing the wind in order to drive ships over water. This practice can be traced back some 7000 years, to ships in the Persian Gulf and on the Nile. Certainly we can go back to sail ships in the Roman times. Then there is renewable energy from hot springs. Geothermal energy has been used for bathing since Paleolithic times and for space heating since ancient Roman times.