<p>(a) The stratospheric ozone layer is a thin layer of ozone that surrounds the Earth. Explain why it is essential for human survival.</p>

<p>(b) If the Earth did not have an atmosphere, would its average surface temperature be higher or lower? Justify your answer.</p>

<p>(c) Electromagnetic waves of different wavelengths have different uses. Give two practical applications of ultraviolet (UV) waves and microwaves.</p>