Explain why the Earth's temperature remains roughly constant over time, in terms of the radiation it absorbs and emits.

AQA GCSE Physics (8463) — 4.6.3 Black body radiation (Phys only) · Explain · 4 marks · View as Markdown

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

The Earth absorbs radiation from the Sun and also emits radiation into space. Scientists model the Earth as acting like a black body.

Model answer (4 marks)

The Earth receives energy from the Sun as incident radiation.
The Earth emits energy as thermal radiation into space.
When the rate of energy absorbed equals the rate of energy emitted, the net energy change is zero.
If the rates are equal, the Earth’s temperature remains constant.

Examiner tips

Use the word ‘absorbs’ for incoming solar radiation and ‘emits’ for outgoing thermal radiation.
Show the equality of rates to justify constant temperature.
Mention the Earth behaves as a black body to justify the emission law.
Keep the explanation concise and directly linked to the points in the mark scheme.

Common mistakes

Confusing absorbed and emitted radiation or using the wrong direction of energy flow.
Failing to state that the rates are equal, thus not explaining why temperature is constant.
Using vague terms like ‘heat’ instead of ‘radiation’ or ‘energy’.

Mark scheme (4 marks)

The Earth absorbs radiation (from the Sun / incident radiation)
The Earth also emits radiation (into space)
The rate of absorption equals the rate of emission
Therefore the temperature stays constant / does not increase or decrease

Key terms in this question

absorbs · emits · radiation

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