The oldest known fossils belong to which organisms?

Explanation

The oldest known fossils are of prokaryotic cells, specifically bacteria, which date back over 3.5 billion years. These ancient microorganisms are critical evidence for understanding the early evolution of life on Earth. Prokaryotes, which include bacteria and archaea, are simple, single-celled organisms that lack a nucleus. They are considered the earliest forms of life, predating more complex organisms. In contrast, viruses are not classified as living organisms and do not fossilize in the same way as cellular life forms. Plants and animals, being more complex and multicellular, appear much later in the fossil record.