How does the sun sustain life on earth?
The sun is what sustains life on earth.  It provides the light needed for plants to grow through photosynthesis.  It is a main source of Vitamin D for humans, and it is a source of energy we can capture on earth and convert into usable electricity through the use of solar panels.  It is what causes weather and climate changes on the earth.  Animals and plants are completely dependent on the sun because it creates the food we need to survive.