Step 1: Understanding the Concept:
The wavelength of radiation emitted by a body depends on its temperature, according to Wien's Law.
Step 2: Detailed Explanation:
The Sun is very hot ($\approx 5800$ K) and emits high-energy, short-wavelength radiation (Visible, UV).
The Earth is much cooler ($\approx 288$ K). Cooler bodies emit lower-energy, longer-wavelength radiation.
Terrestrial radiation (emitted by Earth) falls primarily in the infrared spectrum, which is categorized as longwave radiation (wavelengths $> 4 \mu$m).
Step 3: Final Answer:
Earth's surface primarily emits Longwave (infrared) radiation.