How did the first living things on earth come about?

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

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.

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the backbone of the dna and rna compound is sugar phosphate.