Answer:
Prokaryotes (single celled organisms)
Explanation:
Prokaryotes are single celled organisms or unicellular that lack membrane bound organelles such as the nucleus. Instead their DNA us found in a coiled loop floating freely in the cytoplasm in a region called the nucleoid. Examples that include prokaryotes are Bacteria and Archaea.
They have been estimated to exist on Earth about 3.5 billon years ago where life first started.