- Coal: Coal is formed from the remains of plants that grew in swamps and forests millions of years ago. When these plants died, they were buried under layers of sediment and subjected to high temperatures and pressure. Over time, the plant matter was transformed into coal.
- Oil: Oil is formed from the remains of marine organisms, such as algae and plankton, that lived in ancient oceans. When these organisms died, they sank to the bottom of the ocean and were covered by layers of sediment. Over time, the heat and pressure of the earth's crust caused the organic matter in these organisms to transform into oil.
- Natural gas: Natural gas is formed from the remains of both plants and animals that lived millions of years ago. When these organisms died, they were buried underground and subjected to high temperatures and pressure. Over time, the organic matter in these organisms was transformed into natural gas.
