The sun's radiation interacts with Earth's atmosphere and lifeforms to act as the main source of energy. Solar radiation travels in straight waves. Earth's axis is usually angled to let this energy into its atmosphere so that it can reflect from the surface; if the sun's energy is unable to reach Earth because of its orbit, then ice ages occur.
The solar radiation that reaches Earth acts as its main source of energy in several ways. It warms the Earth's surface, regulating weather systems and providing a habitable environment for its lifeforms to thrive in. The sun's interactions with Earth generate raindrops, which in turn provide hydropower. People have evolved to see objects when light is present. Without the light energy from the sun, this would not be possible.
Solar energy powers the resources people and animals need to survive. It generates hydrocarbons like oil and gas, and it is a source of renewable energy. Without it, life on Earth would not flourish. People use secondary forms of energy that derive from the sun, including fossil fuels, which would not be present if the sun could not play a role in photosynthesis to encourage plant growth.