Explain why the Earth's temperature remains approximately constant over time, rather than continuously increasing as it absorbs radiation from the Sun.

Eduqas GCSE Physics — 6.5 Black body radiation · Explain · 4 marks · View as Markdown

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

The Earth absorbs electromagnetic radiation from the Sun. The Earth also emits radiation back into space.

Model answer (4 marks)

The Earth absorbs energy from the Sun.
The Earth also emits energy as a black‑body into space.
When the rate of absorbed energy equals the rate of emitted energy, a balance is reached.
Thus the temperature remains constant, keeping the Earth in thermal equilibrium.

Examiner tips

Use the word 'absorbs' and 'emits' clearly. Show the balance condition explicitly. Mention black‑body emission. Keep the answer concise and to the point.

Common mistakes

Not stating that the Earth emits as a black body. Failing to mention the equality of absorbed and emitted energy. Using vague terms like 'heat' instead of 'energy'.

Mark scheme (4 marks)

The Earth absorbs radiation from the Sun (or absorbs energy from the Sun)
The Earth also emits/radiates energy (as a black body / into space)
The rate of energy absorbed equals the rate of energy emitted (balance/equilibrium stated)
Therefore the temperature remains constant / stays in thermal equilibrium

Key terms in this question

absorbs