Which heat transfer mechanism is primarily responsible for warming Earth from sunlight?

• A. Conduction
• B. Convection
• C. Radiation
• D. Absorption

Answer: (C)

Sunlight reaches Earth through space by radiation, because there’s no medium in a vacuum to carry heat by touching or moving matter. Radiation is the transfer of energy as electromagnetic waves, which can travel across the empty space between the Sun and Earth. When these waves arrive, the energy is absorbed by the atmosphere and surface, warming them. Conduction and convection require matter to transfer heat, which isn’t how sunlight travels through space. Absorption describes taking in energy once it arrives, but the actual transport of energy from the Sun to Earth is radiation. So the best answer is radiation.