Answer:
Stromatolites are the oldest forms of life for which there is clear fossil evidence.
Step-by-step explanation:
Stromatolites are biogenic sedimentary rocks that are formed by capturing and binding sediment particles or precipitating dissolved substances as a result of the growth and metabolism of microorganisms in a body of water. They are mostly layered and often consist of very finely layered limestone. With their shell-like structure made of tubers, columns or undulating layers, some look like a cauliflower.
The oldest known fossils are mostly stromatolites, and they could therefore provide clues as to how life has developed from very simple to more complex forms.