Alife-form in the precambrian time was

Cynobacteria

Explanation:

The Precambrian time is the earliest period of earth history. It is preceded by the Cambrian time hence got the name. The earliest living organism in the Precambrian time was the Cynobacteria. It has been found in the fossil record of 3.4 billion years ago. They were the primitive organisms which were capable of conducting photosynthesis and producing oxygen. The abundance of Cynobacteria has resulted in the increase in abundance of oxygen into the atmosphere.  

the most common energy conversion is from kinetic energy to potential energy, and then from potential energy to kinetic energy.

later on comes the heat energy, mechanical energy, and other energy conversions.

this energy conversion is so common that we can find it in our day to day lives as well.

- one of the most common energy conversions involves the changing of potential energy to kinetic energy or kinetic energy to potential energy

the fossil record provides evidence of a common ancestor to many species.