Which of the following is NOT considered a renewable energy source?

Natural gas is classified as a non-renewable energy source because it is derived from fossil fuels that have formed over millions of years from the remains of ancient plants and animals. Once extracted and used, natural gas cannot be replenished on a human timescale, leading to depletion of these resources.

In contrast, geothermal, wind power, and hydroelectric energy are all renewable sources. Geothermal energy harnesses heat from beneath the earth's surface, which is continually produced and can be accessed sustainably. Wind power captures energy from wind, an ever-present element, while hydroelectric energy utilizes flowing water to generate electricity, relying on the water cycle that naturally replenishes itself. These renewable resources can be used repeatedly without depleting their availability, making them sustainable options for energy production.