Earth's magnetic field the frequency of earthquakes Earth's tectonic plate activity the composition of the atmosphere
I gave my students this multiple choice question: Which of the following has changed over the last 200 years primarily due to human activity?

Only one answer is correct among these 4 choices:
- Earth's magnetic field
- the frequency of earthquakes
- Earth's tectonic plate activity
- the composition of the atmosphere

Could you tell me which one is correct?

the composition of the atmosphere