Photosynthesis More recent studies, reported in March 2018, also suggest that photosynthesis may have begun about 3.4 billion years ago. The main source of oxygen in the Earth's atmosphere derives from oxygenic photosynthesis, and its first appearance is sometimes referred to as the oxygen catastrophe. Geological evidence suggests that oxygenic photosynthesis, such as that in cyanobacteria, became important during the Paleoproterozoic era around 2 billion years ago. Modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic. Oxygenic photosynthesis uses water as an electron donor, which is oxidized to molecular oxygen () in the photosynthetic reaction center. Several groups of animals
What More Do I Need? finds out through his phone records that there is a number that he calls repeatedly every month. They discover that particular number belongs to Dr. Heller, a criminal psychologist. They attempt to call Dr. Heller posing as an insurance company, planning to get any information from Dr. Heller but failed. However, Dr. Heller is shocked to learn that Dave is currently in Fairview, and decides to book a plane there in the end of the episode. What More Do I Need? "What More Do I Need?" is the 94th episode of the ABC television series, "Desperate Housewives". It is the