Oxygenating the World
The arrival of blue-greens dictated the rest of the development of life. The oxygen they produced accumulated and created the atmosphere as we know it today. Atmospheric oxygen and ozone forms the screen which filters ultra-violet rays which provided the original energy to synthesize the first amino-acids and sugars. From primitive blue-greens the first single-celled organisms evolved (Eukaryots). Such organisms are called protista. Each celled organism is more complex than any bacteria and includes a DNA filled nucleus and elongated bodies called mitochondria which provide energy from burning oxygen. Some of these unicellular organisms have tail or flagellum which resemble the filamentous bacterium called a spirochaetae. These unicellular organisms may also contain chloroplasts (packets of chlorophyll which like blue-greens use energy from sunlight to assemble complex molecules as food for the cell). Consequently each of these tiny unicellular organisms appear to be a committee of simpler organisms. It is even possible that the first cells engulfed and incorporated bacteria and blue-greens to form a communal life (Endosymbiosis). Cells of this complexity first appeared about 1200 million years ago.