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Photosynthesis is a process used by plants and other organisms to convert light energy, normally from the Sun, into chemical energy that can be later released to fuel the organisms' activities. This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water. In most cases, oxygen is also released as a waste product. Photosynthesis maintains atmospheric oxygen levels.
The process always begins when energy from light is absorbed by proteins that contain green chlorophyll pigments. In these light-dependent reactions, some energy is used to strip electrons from suitable substances, such as water, producing oxygen gas. The hydrogen freed by water splitting is used in the creation of two further compounds: reduced nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP), the "energy currency" of cells.
The overall equation for the type of photosynthesis that occurs in plants is as follows:
6 CO2 + 6 H2O - > C6H12O6 + 6 O2
Carbon dioxide + Water plus light photons Sugar + Oxygen
Cyanobacteria is bacteria that obtain their energy through photosynthesis. By producing gaseous oxygen as a by-product of photosynthesis, cyanobacteria are thought to have converted the early reducing atmosphere into an oxidizing one, causing the Great Oxygenation Event, dramatically changing the composition of life forms on Earth by stimulating biodiversity and leading to the near-extinction of anaerobic organisms (that is, oxygen-intolerant). There is an evidence that cyanobacteria were producing oxygen as far back as 2.67 billion years ago.
Synechococcus is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 µm to 1.5 µm. The photosynthetic coccoid cells are preferentially found in well–lit surface waters where it can be very abundant (generally 1,000 to 200,000 cells per millilitre). Many freshwater species of Synechococcus have also been described.
Prochlorococcus is a genus of very small (0.6 µm) marine cyanobacteria with an unusual pigmentation (chlorophyll b). These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosynthetic organism on Earth and responsible for a large percentage of the photosynthetic production of oxygen.
The amount of oxygen in the air is 21%, regardless of the altitude. However, at higher elevation there is a less of air and therefore we pull less of oxygen. At an elevation of 2100 m the atmospheric pressure is about 77% of the sea level and therefore for the same breath we pull only 77% of oxygen. On the peak of Mount Everest, the pressure is only 33% of the sea level.
In South Africa goldmines at depth of over 3.9 km an ancient river deposits are dated to some 2.8 to 3.1 billion years. They contain uranium oxide (UO2), which indicates that at that time there were only “trace” amount of oxygen. The UO2 reacts easily with oxygen, and that’s why we don’t find it rivers today.
Based on analysis of rocks for the contents of uranite it has been noted that concentration of atmospheric oxygen increased substantially around 2.3 to 2.35 billion years ago. It is referred to as the “great oxidation event” (GOE). The exact reason behind it is still being argued about. One theory refers to the evolution of cyano-bacteria. A more convincing theory, and supported by the author relies on combination of Oxygen released from the organic carbon and the reducing flux of gases from the mantle (through volcanos). Once the flax started slowing down an excess oxygen was left in the atmosphere.
Following GOE, with more oxygen, the oxidation of rocks has increased. This in turn liberated enormous quantities of Phosphorus to the oceans, and consequently vast amount of organic matter, and its burial in the rocks.
The high amounts of buried organic carbon represented in turn a huge oxygen sink, drawing down levels of atmospheric oxygen. It’s expected they were less than 10% of the present levels.
Around 580 million years ago the oldest fauna can be found on sea floor, where they operated without light. At that time oxygen rose to at least 15% of present levels.
Around 300 million years ago the land plants become so diversified and developed a series of tough organic molecules like cellulose to grow tall and resist microbial decay. The vast expanses of low-laying swampland collected and buried massive amounts of organic plant debris, and this is why so much coal was formed during that time. During that time the gigantic insects developed.
The drop in oxygen concentration that followed was probably due to changes in paleogeography. A supercontinent called Pangea became fully assembled and as result, far fewer low-laying swampy areas were available. These sandy continental sediments are virtually free of organic matter and thus provides no input of oxygen to the atmosphere. This reduced the supply of oxygen to the atmosphere and drop in oxygen concentration.
Over the last 350 million years, a continuous record of charcoal in continental sedimentary rocks suggests that O2 has always comprised at least ~15% of the atmosphere, because wood cannot burn below this threshold.
In broad outline, oxygen is regulated because an increase in oxygen increases the consumption of oxygen and/or decreases the rate of oxygen production. A decrease in oxygen has opposite effects.
Oxygen and the Rise of Vascular Land Plants. The data of Fig. 2 show a pronounced and extended rise in atmospheric O2 over the period 375–275 mega-annum (Ma) spanning the Carboniferous and Permian periods. What could have brought this rise about? The modelling shows that increased oxygen production caused by increased burial of organic carbon was the chief suspect. This increased burial is attributed to the rise and spread of large woody vascular plants on the continents beginning at about 375 Ma. The plants supplied a new source of organic matter to be buried on land and carried to the oceans via rivers. This ‘‘new’’ carbon was added to that already being buried in the oceans, thus increasing the total global burial flux. This is especially true of lignin, a substance that is decomposed only with difficulty by micro- organisms. The rise of ligniferous plants and an initial level of microbial lignin breakdown lower that that at present may have contributed to increased organic matter burial and better preservation. This high burial rate is reflected by the abundance of coals during this period, which is the greatest abundance in all of earth history.
Another factor favouring extensive Permo-Carboniferous organic matter burial was the presence of vast swamps on the continents, brought about by the presence of extensive poorly drained flatlands, and large areas of coastal plains, brought about by glacially induced fluctuations of sea level. This situation enabled the preservation of organic debris, leading ultimately to coal formation, because of the relative lack of organic decay in stagnant anoxic waters. Why coal formation, organic burial, and oxygen production dropped toward the end of the Permian period (Fig. 2) is not clear, but it may be tied up with sea level drop and a general drying of the continents.
The level of atmospheric oxygen cannot rise indefinitely unless the frequency of forest fires becomes so excessive that plant life cannot persist. Fossil charcoal, as evidence of paleo fires, has been found for all times that trees have populated the land, and the lower limit for the production of charcoal has been estimated to be at about 13% O2.
The process always begins when energy from light is absorbed by proteins that contain green chlorophyll pigments. In these light-dependent reactions, some energy is used to strip electrons from suitable substances, such as water, producing oxygen gas. The hydrogen freed by water splitting is used in the creation of two further compounds: reduced nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP), the "energy currency" of cells.
The overall equation for the type of photosynthesis that occurs in plants is as follows:
6 CO2 + 6 H2O - > C6H12O6 + 6 O2
Carbon dioxide + Water plus light photons Sugar + Oxygen
Cyanobacteria is bacteria that obtain their energy through photosynthesis. By producing gaseous oxygen as a by-product of photosynthesis, cyanobacteria are thought to have converted the early reducing atmosphere into an oxidizing one, causing the Great Oxygenation Event, dramatically changing the composition of life forms on Earth by stimulating biodiversity and leading to the near-extinction of anaerobic organisms (that is, oxygen-intolerant). There is an evidence that cyanobacteria were producing oxygen as far back as 2.67 billion years ago.
Synechococcus is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 µm to 1.5 µm. The photosynthetic coccoid cells are preferentially found in well–lit surface waters where it can be very abundant (generally 1,000 to 200,000 cells per millilitre). Many freshwater species of Synechococcus have also been described.
Prochlorococcus is a genus of very small (0.6 µm) marine cyanobacteria with an unusual pigmentation (chlorophyll b). These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosynthetic organism on Earth and responsible for a large percentage of the photosynthetic production of oxygen.
The amount of oxygen in the air is 21%, regardless of the altitude. However, at higher elevation there is a less of air and therefore we pull less of oxygen. At an elevation of 2100 m the atmospheric pressure is about 77% of the sea level and therefore for the same breath we pull only 77% of oxygen. On the peak of Mount Everest, the pressure is only 33% of the sea level.
In South Africa goldmines at depth of over 3.9 km an ancient river deposits are dated to some 2.8 to 3.1 billion years. They contain uranium oxide (UO2), which indicates that at that time there were only “trace” amount of oxygen. The UO2 reacts easily with oxygen, and that’s why we don’t find it rivers today.
Based on analysis of rocks for the contents of uranite it has been noted that concentration of atmospheric oxygen increased substantially around 2.3 to 2.35 billion years ago. It is referred to as the “great oxidation event” (GOE). The exact reason behind it is still being argued about. One theory refers to the evolution of cyano-bacteria. A more convincing theory, and supported by the author relies on combination of Oxygen released from the organic carbon and the reducing flux of gases from the mantle (through volcanos). Once the flax started slowing down an excess oxygen was left in the atmosphere.
Following GOE, with more oxygen, the oxidation of rocks has increased. This in turn liberated enormous quantities of Phosphorus to the oceans, and consequently vast amount of organic matter, and its burial in the rocks.
The high amounts of buried organic carbon represented in turn a huge oxygen sink, drawing down levels of atmospheric oxygen. It’s expected they were less than 10% of the present levels.
Around 580 million years ago the oldest fauna can be found on sea floor, where they operated without light. At that time oxygen rose to at least 15% of present levels.
Around 300 million years ago the land plants become so diversified and developed a series of tough organic molecules like cellulose to grow tall and resist microbial decay. The vast expanses of low-laying swampland collected and buried massive amounts of organic plant debris, and this is why so much coal was formed during that time. During that time the gigantic insects developed.
The drop in oxygen concentration that followed was probably due to changes in paleogeography. A supercontinent called Pangea became fully assembled and as result, far fewer low-laying swampy areas were available. These sandy continental sediments are virtually free of organic matter and thus provides no input of oxygen to the atmosphere. This reduced the supply of oxygen to the atmosphere and drop in oxygen concentration.
Over the last 350 million years, a continuous record of charcoal in continental sedimentary rocks suggests that O2 has always comprised at least ~15% of the atmosphere, because wood cannot burn below this threshold.
In broad outline, oxygen is regulated because an increase in oxygen increases the consumption of oxygen and/or decreases the rate of oxygen production. A decrease in oxygen has opposite effects.
Oxygen and the Rise of Vascular Land Plants. The data of Fig. 2 show a pronounced and extended rise in atmospheric O2 over the period 375–275 mega-annum (Ma) spanning the Carboniferous and Permian periods. What could have brought this rise about? The modelling shows that increased oxygen production caused by increased burial of organic carbon was the chief suspect. This increased burial is attributed to the rise and spread of large woody vascular plants on the continents beginning at about 375 Ma. The plants supplied a new source of organic matter to be buried on land and carried to the oceans via rivers. This ‘‘new’’ carbon was added to that already being buried in the oceans, thus increasing the total global burial flux. This is especially true of lignin, a substance that is decomposed only with difficulty by micro- organisms. The rise of ligniferous plants and an initial level of microbial lignin breakdown lower that that at present may have contributed to increased organic matter burial and better preservation. This high burial rate is reflected by the abundance of coals during this period, which is the greatest abundance in all of earth history.
Another factor favouring extensive Permo-Carboniferous organic matter burial was the presence of vast swamps on the continents, brought about by the presence of extensive poorly drained flatlands, and large areas of coastal plains, brought about by glacially induced fluctuations of sea level. This situation enabled the preservation of organic debris, leading ultimately to coal formation, because of the relative lack of organic decay in stagnant anoxic waters. Why coal formation, organic burial, and oxygen production dropped toward the end of the Permian period (Fig. 2) is not clear, but it may be tied up with sea level drop and a general drying of the continents.
The level of atmospheric oxygen cannot rise indefinitely unless the frequency of forest fires becomes so excessive that plant life cannot persist. Fossil charcoal, as evidence of paleo fires, has been found for all times that trees have populated the land, and the lower limit for the production of charcoal has been estimated to be at about 13% O2.
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