According to the fossil record on earth, the earliest-known life-forms were primitive

The fossilized microorganisms found in the hydroscopic vents.

Explanation:

These life forms are known to have been first appeared the earth and thus they were in the firms of the earth at least about the 3.77 billion and old as  4.28 billion years. And these microfossils were found in the primitive rocks formed near the Australian origin. They were in the appearance of the bacteria the single-celled worms and the hydro thermal vents provided them with the adaptable conditions of their growth and development.