Methane and carbon dioxide are both described as greenhouse gases. Describe the greenhouse effect and explain why greenhouse gases are necessary for life on Earth.

Pearson Edexcel International GCSE Chemistry (4CH1) — 2.3 Gases in the atmosphere · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Greenhouse gases, such as methane and carbon dioxide, absorb and re‑emit infrared radiation emitted by the Earth’s surface, trapping heat in the atmosphere.

This absorption raises the average temperature of the atmosphere.

If greenhouse gases were absent, the Earth’s surface would be far colder, with temperatures too low for liquid water.

Thus, greenhouse gases keep the planet warm enough to support life and allow biological processes to occur.

Examiner tips

  • Use the exact phrase "trap infrared radiation" and "raise the temperature". Mention the consequence of a cold Earth. Show the link to liquid water and life. Keep each point brief and to the point.

Common mistakes

  • Confusing greenhouse gases with all atmospheric gases. Forgetting to mention the role of liquid water. Using vague terms like "keep warm" without explaining the mechanism.

Mark scheme (4 marks)

  1. Greenhouse gases trap infra-red radiation (from the Earth's surface)
  2. This causes an increase in the temperature of the Earth's atmosphere
  3. Without greenhouse gases temperatures on Earth would be too low / the Earth would be too cold
  4. Greenhouse gases maintain temperatures on Earth high enough to support life (allowing liquid water / biological processes to exist)

Key terms in this question

greenhouse effect · greenhouse gases

Related

More Gases in the atmosphere questions

▶ Try answering this question with AI marking (free) →