What does the greenhouse effect involve?

The greenhouse effect is a critical atmospheric process that helps regulate Earth's temperature. It is primarily characterized by the role of greenhouse gases, such as carbon dioxide and methane, which trap heat in the atmosphere. When sunlight reaches the Earth, it is absorbed by the surface and subsequently re-radiated as infrared radiation. Greenhouse gases absorb some of this infrared radiation and re-radiate it back toward the Earth's surface. This process is essential for maintaining a temperature that can support life, as it prevents a significant amount of heat from escaping into space.

While the other options describe different atmospheric phenomena, they do not accurately define the greenhouse effect. The depletion of oxygen in the atmosphere does not relate to the trapping of heat. Absorption of sunlight by the oceans refers to how bodies of water can warm under sunlight but does not involve the gases in the atmosphere. The scattering of light by atmospheric particles is a separate physical process that affects the color and clarity of the atmosphere rather than the retention of heat. The correct answer thus highlights the critical mechanism by which atmospheric gases maintain Earth's temperature through the trapping and returning of infrared radiation.