Underground deposits of combustible carbon-based matter used as an energy source include oil, natural gas, coal, and peat. What is this called?

• A. Fossil fuel
• B. Biomass
• C. Food web
• D. Predation

Answer: (A)

Fossil fuels are energy-rich carbon-based substances formed from ancient organisms buried and transformed by heat and pressure over long periods. Oil, natural gas, coal, and peat all fit this description because they originate from biological material that was buried underground and then altered by geological processes to become combustible fuels. Peat is included because it is an early stage in coal formation; with continued burial and heat, peat gradually becomes coal. Oil and natural gas come from microscopic organisms that settled in ancient seas and, over millions of years, were converted into hydrocarbons. These fuels are nonrenewable resources because their formation requires timescales far exceeding human lifespans. Biomass refers to modern organic matter like wood or crop waste used for energy, not ancient underground deposits. The other terms describe ecological interactions, not energy sources.