The earliest known life forms on earth were a kind hetorotrophs. They were single-celled organisms who lived in the atmosphere. Hetorotrophs are unable to manufacture their own food, but rather consume the inorganically formed amino acids and other organic material, which later provided the basic food eaten by all hetorotrophs- including humans. These earliest hetorotrophs provided the foundation for all later life. All later life forms evolved from these primitive hetorotrophs.