Final answer:
The Sun imparts photons continuously to the upper atmosphere, which helps heat the Earth's surface and maintain the greenhouse effect.
Step-by-step explanation:
The Sun imparts photons continuously to the upper atmosphere.
The photons generated by fusion reactions in the solar interior travel a short distance before being absorbed or scattered by atoms and sent off in random directions. It takes between 100,000 and 1,000,000 years for energy to make its way from the center of the Sun to its surface.
These photons are essential in heating the Earth's surface and maintaining the greenhouse effect, which keeps the surface temperature about 40°C higher than it would be without the absorption of solar radiation.