Fossil fuels come from ancient dead plants and tiny sea creatures that were buried, squashed, and heated deep underground over millions of years, turning their remains into coal, oil, and natural gas. They do not mainly come from dinosaurs, despite the name and some popular logos.

Basic idea

  • Fossil fuels are made of the carbon-rich remains of organisms that lived hundreds of millions of years ago.
  • Over very long times, heat and pressure inside Earth transformed these buried remains into coal, petroleum (crude oil), and natural gas.

Where coal comes from

  • Coal mostly comes from ancient swamp forests full of large plants and ferns that died, piled up in wetlands, and formed thick, soggy layers called peat.
  • As more sediment buried this peat, rising temperature and pressure slowly changed it into different types of coal over millions of years.

Where oil and gas come from

  • Oil and natural gas mostly come from microscopic plants and animals (plankton) that lived in ancient seas and lakes, died, and settled to the seafloor in low-oxygen mud.
  • Buried deeper and deeper, their remains first became a waxy material called kerogen, then transformed into liquid crude oil and, at higher temperatures, into natural gas.

Why they are “non-renewable”

  • The geological processes that turn dead organisms into fossil fuels take millions of years, far longer than the time in which humans are burning them.
  • Because they form so slowly and are being used very quickly, fossil fuels are considered non-renewable energy resources.

Quick myth check

  • The word “fossil” in “fossil fuels” refers broadly to very old organic remains, not specifically to dinosaur skeletons.
  • Most of the carbon in today’s fossil fuels comes from ancient algae, bacteria, and plants, not dinosaur bodies.

TL;DR: Fossil fuels are ancient sunlight stored in long-dead plants and microscopic sea life, turned by heat and pressure into coal, oil, and gas over millions of years.