This document discusses non-renewable or conventional energy sources, which include fossil fuels like coal, petroleum, and natural gas. Coal is a nonrenewable resource that formed over millions of years from decaying plant and animal matter and cannot be replenished on a scale comparable to its consumption. Similarly, petroleum and natural gas are considered nonrenewable as they take significant time to form from fossil remains and cannot be replenished quickly enough to match consumption. The document asks how coal, oil, and gas are formed from fossil remains over long periods of geological time.