Prokaryotes are very simple cells.
These cells represent the earliest form of living cells on earth, yet they are found everywhere. They are found in the soil, the air, the water, and in or on every organism on the face of the earth, including humans. Prokaryotes also inhabit extreme environments such as salt flats, hot springs, and also thermal vents located deep within the earth. Prokaryotic cells are microscopic in size, averaging in size from 1 to 10 micrometers in length. These cells lack membrane- enclosed internal structures.