Where do most living things get the food they need for life?

I believe the answer is Sunlight.
In our world, the bimass of plants (which considered as living things) make up 1000 more population compared to another living organism.
The plants get their food mainly from the photosynthesis process that utilize Sunlight, water, and other nutrients from soil.

Giga is the second highest prefix on the normal scale, the first is terra.