Cyanobacteria, Rocks and Oxygen
Cyanobacteria make energy from sunlight through photosynthesis, which creates oxygen as a waste product. As the cyanobacteria thrive, more and more oxygen is created. However, overly high oxygen levels can poison the cyanobacteria, killing the cells. During Earth's early history when cyanobacteria first evolved, the oxygen levels eventually decreased until they attained a level compatible with cyanobacteria growth.
According to the NASA article, Iron Record: Ancient Rocks Tell the Story of Oxygen, and Life, this cycle of growth and decline is evident in the rocks that formed during the Precambrian period on Earth. These ancient rocks display the concentration of iron gradually increasing as the cyanobacteria population thrived, then the iron bands abruptly stop, which suggests that when the oxygen levels were too high, the cyanobacteria quickly died off.
Rock composition allows scientists to determine the environmental conditions during a given period of time. Rock composition is dependent upon the environment in which a rock is formed. Oceans containing more dissolved oxygen will create different types of rocks than oceans that are oxygen free.
Iron and the Ocean
Iron is one of the most abundant metals on the planet, making up roughly five percent of the Earth's crust. It occurs in many minerals and ores, including hematite, magnetite, pyrite, limonite and siderite. All organisms on earth use iron in some way or another. Animals use iron-rich proteins during redox reactions involved in the formation of energy (ATP), which is used to drive life processes. Iron is found in high concentrations in many soils and rocks and in some groundwater as dissolved iron, but occurs in limited amounts in the ocean.
Iron is necessary for life but is scarce in the ocean. Sunlight plays an important role in helping to cycle iron and make it available to marine plants and animals. Sunlight energy transforms iron-which molecules into more loosely-bound configurations of iron allowing bacteria, plankton, phytoplankton and other microorganisms to easily take hold of and use the iron. Bacteria need to manufacture small molecules, siderophores, to help them obtain iron from their environment.
Photosynthesis is the transformation of energy from sunlight into chemical energy of the cell in the form of ATP and includes the production of cell biomass by CO
fixation. Oxygen is produced as a waste product of photosynthesis with the 'O' in oxygen coming from the water. Three key components to photosynthesis are sunlight, carbon dioxide and water (H
O). Plants, algae or photoautotrophic bacteria will strip elections from water molecules to make ATP and transfer the electrons to carbon dioxide, This process involves the conversion of energy from sunlight, water and carbon dioxide into sugar, which is an organic compound, and releases oxygen as a waste product.
Sugar produced by photosynthesis is a source of carbohydrates, and is also used to make fats and proteins. Many living things on the earth depend on these fats, proteins and carbohydrates to derive their basic source of energy. Many living things are dependent upon the process of photosynthesis in order for them to thrive. Photosynthesis takes carbon dioxide from the atmosphere, creates energy, which makes it possible for mammals to live on earth and replenishes the oxygen in the earth's atmosphere.
Carbon is constantly being recycled in order to produce organic compounds, which all living things are made up of and need in order to survive. Key components of the carbon cycle include photosynthetic organisms and microorganisms. Photosynthetic organisms take in carbon in the form of carbon dioxide and covert the carbon dioxide into carbohydrates using the sun's energy and chlorophyll pigments. These organisms are then consumed by animals, fish and humans, who in turn use the carbohydrates for energy and further convert the remaining carbon to cellular biomass. Some carbon dioxide is released into the atmosphere during cellular respiration, however a large portion of the carbon is returned to the ground as animals and plants die. Many bacterial cells, fungi and other microorganisms will consume the dead organic matter and release atmospheric carbon dioxide, which is reused by the plants.
The transformation of nitrogen is essential for all life on earth. It is the vital component in nucleic acids and amino acids. Nitrogen is the most common gas in our atmosphere, however animals and many plants cannot use nitrogen in its gaseous form. The nitrogen cycle depends on microorganisms, which trap the nitrogen.
The nitrogen cycle begins with nitrogen fixation, the trapping of nitrogen gas from the atmosphere by bacteria like cyanobacteria. Previously trapped or fixed and therefore bioavilable, nitrogen comes from dead plants and animals in the soil. During the process of nitrogen fixation microorganisms in the water and the soil play an important role because they contain the enzyme systems needed to trap the atmospheric nitrogen and convert it into compounds that can be used by plants. The gaseous nitrogen is transformed to ammonia, which is used to fertilize plants.
Nitrogen is also found in the soil as urea, which is contained in urine. Soil bacteria and other microorganisms will process the urea, forming a mixture of amino acids. The amino acids are then broken down by microbial metabolism and the accumulated ammonia can be used directly by plants.
Finally, mineralization occurs, the process whereby complex organic compounds are converted into inorganic compounds and ammonia. The majority of the ammonia is transformed into nitrite ions by bacteria called Nitrosomonas, during which the bacterial cells gain energy for their metabolic needs. The nitrite ions are transformed and further oxidized to nitrate ions by Nitrobacter, which again gains energy from the process. The nitrate is used by plants as a nutrient or can be freed into atmospheric nitrogen by certain microorganisms, including denitrifying bacteria.
The water cycle is the constant movement of water rotating between the surface of the earth and the atmosphere. The water cycle is made up of several stages, evaporation, condensation, and precipitation. Water from lakes, ponds, and other bodies of water evaporates as the water absorbs energy in the form of heat from the sun; the water then changes into a gas, water vapor. Air containing water vapor will rise and begin to cool because it is losing heat. Once it has lost enough heat it will condense or become a liquid again in the form of tiny water droplets. The droplets form clouds. As the droplets in the cloud grow, they will become too big to stay in the atmosphere. The cloud will release precipitation in the form of rain or snow depending on the atmospheric temperature. Then the cycle will begin all over again.
All organisms play a role in the cycling of iron in some way, including plankton, bacteria and other microorganisms. Plants on land obtain their iron from the soil and then organisms eat these plants. Another organism eats the previous organisms, which ate the plant. Eventually the organisms will die and decompose, the decaying matter will release minerals back into the soil. The cycle will then continue and repeat. In the ocean, iron is consumed as the sun breaks down the iron at the surface into loosely configured atoms of iron and oxygen. The loosely configured particles allow bacteria, plankton, phytoplankton and other microorganisms to consume the iron.