Fractionation of carbon isotopes in oxygenic photosynthesis characterization of food chains. Oxygenic photosynthesis is a metabolic pathway facilitated by autotrophs, including plants, algae, and cyanobacteria. This pathway converts inorganic carbon dioxide from the atmosphere or aquatic environment into carbohydrates, using water and energy from light, then releases molecular oxygen as a product. Organic carbon contains less of the stable isotope Carbon-13, or C, relative to the initial inorganic carbon from the atmosphere or water because photosynthetic carbon fixation involves several fractionating reactions with kinetic isotope effects. These reactions undergo a kinetic isotope effect because they are limited by overcoming an activation energy barrier. The lighter isotope has
Carbon dioxide in Earth's atmosphere actual surface temperature of approximately 14 °C (57.2 °F). Carbon dioxide is believed to have played an important effect in regulating Earth's temperature throughout its 4.7 billion year history. Early in the Earth's life, scientists have found evidence of liquid water indicating a warm world even though the Sun's output is believed to have only been 70% of what it is today. It has been suggested by scientists that higher carbon dioxide concentrations in the early Earth's atmosphere might help explain this faint young sun paradox. When Earth first formed, Earth's atmosphere may have contained more greenhouse gases and concentrations