Natural gas, coal and petroleum are all fossil fuels. Describe how fossil fuels are formed and explain why they are described as non-renewable.

Cambridge International IGCSE Chemistry (0620) — 11.3 Fuels · Describe and Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Fossil fuels are formed from the remains of ancient plants and/or animals that have been buried under layers of rock or sediment.

Over millions of years these remains are subjected to heat and pressure, which transforms them into coal, oil or natural gas.

Because the process takes millions of years, the fuels are not replenished on a human timescale.

They are therefore described as non‑renewable, as the rate at which we use and burn them far exceeds the rate at which new fuel can be formed.

Examiner tips

  • Use the exact terms ‘ancient plants and/or animals’, ‘buried’, ‘heat and pressure’, ‘millions of years’ and ‘non‑renewable’. Show the cause–effect link: burial → heat/pressure → formation → long timescale → non‑renewable.
  • common_mistakes
  • :
  • Confusing renewable with non‑renewable or omitting the timescale. Using vague phrases like ‘burned quickly’ instead of ‘used faster than replenished’.

Mark scheme (4 marks)

  1. Fossil fuels formed from the remains of ancient plants and/or animals (organisms)
  2. Over millions of years, buried under layers of rock/sediment, subjected to heat and pressure
  3. Fossil fuels take millions of years to form
  4. They are being used/burned faster than they can be replaced/reformed, so stocks will eventually run out

Key terms in this question

fossil fuel · non-renewable · petroleum

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