As oxygenic photosynthesis spread through the oceans, everything that could be oxidized by oxygen was, during what is called the (“GOE”), although there may have been multiple dramatic events. The event began as long as three bya and is . The ancient carbon cycle included volcanoes spewing a number of gases into the atmosphere, including hydrogen sulfide, sulfur dioxide, and hydrogen, but carbon dioxide was particularly important. When the continents began forming, carbon dioxide was removed from the atmosphere via water capturing it, , the carbon became combined into calcium carbonate, and plate tectonics subducted the calcium carbonate in the ocean sediments into the crust, which was again released as carbon dioxide in volcanoes.
When cyanobacteria began using water in photosynthesis, carbon was captured and oxygen released, which began the oxygenation of Earth's atmosphere. But the process may have not always been a story of continually increasing atmospheric oxygen. There may have been wild swings. Although the process is indirect, oxygen levels are influenced by the balance of carbon and other elements being buried in ocean sediments. If carbon is buried in sediments faster than it is introduced to the atmosphere, oxygen levels will increase. is comprised of iron and sulfur, but in the presence of oxygen, pyrite's iron combines with oxygen (and becomes iron oxide, also known as rust) and the sulfur forms sulfuric acid. Pyrite burial may have acted as the dominant oxygen source before carbon burial did. There is sulfur isotope evidence that Earth had almost no atmospheric oxygen before 2.5 bya.
More carbon dioxide was removed from the atmosphere by those processes than was reintroduced to the atmosphere by volcanism and other processes. That removal and reintroduction of carbon to Earth’s surface is called the . As carbon dioxide continues to be removed from the atmosphere, life will have a harder time surviving, to eventually go extinct, as first plants, then animals decline and go extinct, and it will be back to microbes ruling the Earth until the Sun’s expansion into a red giant destroys Earth. The earthly end of complex life’s reign may be a billion years away, but might come much sooner.
In the earliest days of life on Earth, it had to solve the problems of how to reproduce, how to separate itself from its environment, how to acquire raw materials, and how to make the chemical reactions that it needed. But it was confined to those areas where it could take advantage of briefly available potential energy as . The earliest process of skimming energy from energy gradients to power life is called respiration. That earliest respiration is today called because there was virtually no free oxygen in the atmosphere or ocean in those early days. Respiration was life’s first energy cycle. A biological energy cycle begins by harvesting an energy gradient (usually by a proton crossing a membrane or, in photosynthesis, directly capturing photon energy), and the acquired energy powered chemical reactions. The cycle then proceeds in steps, and the reaction products of each step sequentially use a little more energy from the initial capture until the initial energy has been depleted and the cycle’s molecules are returned to their starting point and ready for a fresh influx of energy to repeat the cycle.
The evidence is that after “only” 100 million years or so after LUCA lived, life learned its next most important trick after learning how to exist and speed up reactions: it tapped a new energy source. Photosynthesis may . Bacteria are true photosynthesizers that fix carbon from captured sunlight. Archaeans , so are not photosynthesizers, even those that capture photons.
Any chemical process involves a change in chemical bonds and the related bond energies and thus in the total chemical binding energy. This change is matched by a difference between the total kinetic energy of the set of reactant molecules before the collision and that of the set of product molecules after the collision (conservation of energy). Some reactions release energy (e.g., burning fuel in the presence of oxygen), and others require energy input (e.g., synthesis of sugars from carbon dioxide and water).
I have koi in outside fish ponds. At times during the long summer days there is an occurrence called an algae bloom where the water in the pond becomes filled with very small suspended algae. During the day there is no problem with the respiration of the koi that I have in the pond… but because the algae use up so much available oxygen during the night and do not add any O2 to the water…my koi in the very early morning hours before the sunlight starts photosynthesis of the algae run out of the amount of oxygen they need for respiration and are forced to breathe atmospheric O2 at the surface of the pond! They gasp for O2 out of the water from the atmosphere where there is enough available for them to survive. My point is in water ponds there is a semi closed environment where plants can use up so much oxygen at night that they force the fish to get their oxygen elsewhere. When days become shorter the algae bloom will naturally diminish if I wait it out and do not do massive water changes or resort to killing the floating algae with a chemical plant killer algaecide that will not kill my fish if used in the proper doses. Plants do use O2 at night and do not give off any O2 in darkness!
Understanding chemical reactions and the properties of elements is essential not only to the physical sciences but also is foundational knowledge for the life sciences and the earth and space sciences. The cycling of matter and associated transfers of energy in systems, of any scale, depend on physical and chemical processes. The reactivity of hydrogen ions gives rise to many biological and geophysical phenomena. The capacity of carbon atoms to form the backbone of extended molecular structures is essential to the chemistry of life. The carbon cycle involves transfers between carbon in the atmosphere—in the form of carbon dioxide—and carbon in living matter or formerly living matter (including fossil fuels). The proportion of oxygen molecules (i.e., oxygen in the form O2) in the atmosphere also changes in this cycle.
In plants, algae and cyanobacteria, sugars are produced by a subsequent sequence of light-independent reactions called the , but some bacteria use different mechanisms, such as the . In the Calvin cycle, atmospheric carbon dioxide is into already existing organic carbon compounds, such as (RuBP). Using the ATP and NADPH produced by the light-dependent reactions, the resulting compounds are then and removed to form further carbohydrates, such as .
Naturally occurring food and fuel contain complex carbon-based molecules, chiefly derived from plant matter that has been formed by photosynthesis. The chemical reaction of these molecules with oxygen releases energy; such reactions provide energy for most animal life and for residential, commercial, and industrial activities.
. The chemical reaction by which plants produce complex food molecules (sugars) requires an energy input (i.e., from sunlight) to occur. In this reaction, carbon dioxide and water combine to form carbon-based organic molecules and release oxygen. (Boundary: Further details of the photosynthesis process are not taught at this grade level.)