Sunlight is the primary source of energy on our planet.
This energy is used by plants, algae and cyanobacteria to do photosynthesis that convert carbon dioxide and water into organic compounds like carbohydrates.
It provides the energy to keep the earth's atmosphere warm and inhabitable.
The sunlight and its heating of the atmosphere affects the weather all over the world.
The intensity of sunlight controls growth of plant, and the light duration affects the flowering of plant and habits in animals and insects.
It is important for the water cycle. The water cycle includes water in the form that we drink as well as in forms of vapor and ice.
This vapor is stored in the clouds and the clouds return it in form of rain or snow which get stored underground or in the waterbodies.