What is the original source of the energy that flows through most ecosystems? What would happen without this source?

The sun and its light is usually the original source of energy. Without it, most if not all of life on earth would be wiped out.

Explanation:

Taking the example of humans and our survival through eating meat such as cows, we can observe the sun's effect on the food chain. The sun provides the light energy needed for plants such as grass to do photosynthesis and make their own food source. Cows eat the grass. Humans eat cows. Without the sun none of this would be possible.