Final answer:
Prokaryotes, including Bacteria and Archaea, are considered the earliest single-celled organisms and potential ancestors of all life on Earth. They resemble the first life forms that appeared around 4 billion years ago.
Step-by-step explanation:
Prokaryotes are single-celled organisms that exist today and resemble what scientists believe could have been the ancestor creature of all life on Earth. The earliest living things on Earth were single-celled organisms, which appeared around 4 billion years ago. These were the most complex forms of life on Earth for approximately 1 billion years. There are two distinct groups of these microorganisms: Bacteria and Archaea, with Archaea including microbes that live in extreme conditions. It is believed that prokaryotic cells were the first organisms on our planet, originating about 3.5 billion years ago. These cells did not possess nuclei, unlike the nucleated cells that appeared later, about 1.5 billion years ago, marking the start of an evolutionary diversification.