Answer: single-celled micro-organisms or microbes lacking a cell nucleus or cell membrane known as prokaryotes, seem to have first appeared on Earth almost four billion years ago
Step-by-step explanation:
Most of them are formed when large mats of microorganisms, known as microbial mats, trap sedimentary grains together. These microorganisms are usually cyanobacteria, a type of bacteria also known as blue-green algae. Cyanobacteria use the process of photosynthesis to obtain energy.