Instruct: Given a question, retrieve documents that can help answer the question.
Query: Who first identified oxygen?
Oxygen was isolated by Michael Sendivogius before 1604, but it is commonly believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, and Joseph Priestley in Wiltshire, in 1774. Priority is often given for Priestley because his work was published first. Priestley, however, called oxygen "dephlogisticated air", and did not recognize it as a chemical element. The name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and correctly characterized the role it plays in combustion.
Oxygen is required by people for normal cell metabolism. Air is typically 21% oxygen by volume. This is normally sufficient, but in some circumstances the oxygen supply to tissues is compromised. 
Oxygen therapy, also known as supplemental oxygen, is the use of oxygen as a medical treatment. This can include for low blood oxygen, carbon monoxide toxicity, cluster headaches, and to maintain enough oxygen while inhaled anesthetics are given. Long term oxygen is often useful in people with chronically low oxygen such as from severe COPD or cystic fibrosis. Oxygen can be given in a number of ways including nasal cannula, face mask, and inside a hyperbaric chamber. 
High concentrations of oxygen can cause oxygen toxicity such as lung damage or result in respiratory failure in those who are predisposed. It can also dry out the nose and increase the risk of fires in those who smoke. The target oxygen saturation recommended depends on the condition being treated. In most conditions a saturation of 94-98% is recommended, while in those at risk of carbon dioxide retention saturations of 88-92% are preferred, and in those with carbon monoxide toxicity or cardiac arrest the saturation should be as high as possible.
The use of oxygen in medicine become common around 1917. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The cost of home oxygen is about US$150 a month in Brazil and US$400 a month in the United States. Home oxygen can be provided either by oxygen tanks or an oxygen concentrator. Oxygen is believed to be the most common treatment given in hospitals in the developed world.
In 1774, Joseph Priestley discovered that oxygen was released by heating mercuric oxide, although he did not identify the gas as oxygen (rather, Priestley called it "dephlogisticated air," as that was the paradigm that he was working under at the time).
An oxygen concentrator has an air compressor, two cylinders filled with zeolite pellets, a pressure equalizing reservoir, and some valves and tubes. In the first half-cycle the first cylinder receives air from the compressor, which lasts about 3 seconds. During that time the pressure in the first cylinder rises from atmospheric to about 2.5 times normal atmospheric pressure (typically 20 psi/138 kPa gauge, or 2.36 atmospheres absolute) and the zeolite becomes saturated with nitrogen. As the first cylinder reaches near pure oxygen (there are small amounts of argon, CO, water vapour, radon and other minor atmospheric components) in the first half-cycle, a valve opens and the oxygen-enriched gas flows to the pressure equalizing reservoir, which connects to the patient's oxygen hose. At the end of the first half of the cycle, there is another valve position change so that the air from the compressor is directed to the second cylinder. The pressure in the first cylinder drops as the enriched oxygen moves into the reservoir, allowing the nitrogen to be desorbed back into gas. Partway through the second half of the cycle, there is another valve position change to vent the gas in the first cylinder back into the ambient atmosphere, keeping the concentration of oxygen in the pressure equalizing reservoir from falling below about 90%. The pressure in the hose delivering oxygen from the equalizing reservoir is kept steady by a pressure reducing valve.
Tetraoxygen had been suspected to exist since the early 1900s, when it was known as oxozone. It was identified in 2001 by a team led by Fulvio Cacace at the University of Rome. The molecule was thought to be in one of the phases of solid oxygen later identified as . Cacace's team suggested that probably consists of two dumbbell-like molecules loosely held together by induced dipole dispersion forces.
A silicon–oxygen tetrahedron is the SiO anionic group, or a silicon atom with four surrounding oxygen atoms arranged to define the corners of a tetrahedron. This is a fundamental component of most silicates in the Earth's crust. A variety of silicate minerals can be identified by the way that the tetrahedra links differ, also by the cations present in the mineral.
Multiple oxygen sensors with independent circuitry reduce the risk of losing information on oxygen partial pressure. An electronically controlled CCR generally uses a minimum of three oxygen monitors to ensure that if one fails, it will be able to identify the failed cell with reasonable reliability.
Courtois gave samples to his friends, Charles Bernard Desormes (1777–1838) and Nicolas Clément (1779–1841), to continue research. He also gave some of the substance to chemist Joseph Louis Gay-Lussac (1778–1850), and to physicist André-Marie Ampère (1775–1836). On 29 November 1813, Desormes and Clément made Courtois' discovery public. They described the substance to a meeting of the Imperial Institute of France. On 6 December, Gay-Lussac announced that the new substance was either an element or a compound of oxygen. It was Gay-Lussac who suggested the name ""iode"", from the Greek word ("ioeidēs") for violet (because of the colour of iodine vapor). Ampère had given some of his sample to English chemist Humphry Davy (1778–1829), who experimented on the substance and noted its similarity to chlorine. Davy sent a letter dated 10 December to the Royal Society of London stating that he had identified a new element. Arguments erupted between Davy and Gay-Lussac over who identified iodine first, but both scientists acknowledged Courtois as the first to isolate the element.
The most widely accepted chronology of the Great Oxygenation Event suggests that free oxygen was first produced by prokaryotic and then later eukaryotic organisms that carried out photosynthesis more efficiently, producing oxygen as a waste product. The first oxygen-producing organisms arose long before the GOE, perhaps as early as .
In humans, there are three isoforms of hypoxia-inducible factor-proline dioxygenase. These are PHD1, PHD2 and PHD3. PHD2, in particular, was identified as the most important human oxygen sensors due to its slow reaction with oxygen.
Many training agencies such as PADI, CMAS, SSI and NAUI train their divers to personally check the oxygen percentage content of each nitrox cylinder before every dive. If the oxygen percentage deviates by more than 1% from the planned mix, the diver must either recalculate the dive plan with the actual mix, or else abort the dive to avoid increased risk of oxygen toxicity or decompression sickness. Under IANTD and ANDI rules for use of nitrox, which are followed by most dive resorts around the world, filled nitrox cylinders are signed out personally in a gas blender log book, which contains, for each cylinder and fill, the cylinder number, the measured oxygen percent composition, the signature of the receiving diver (who should have personally measured the oxygen fraction before taking delivery), and the calculated maximum operating depth for that mix. All of these steps minimize danger but increase complexity of operations as each diver must use the specific cylinder they have checked out.
In South Africa, the national standard for handling and filling portable cylinders with pressurised gases (SANS 10019) requires that the cylinder be labelled with a sticker identifying the contents as nitrox, and specifying the oxygen fraction. Similar requirements may apply in other countries.
Retinopathy of prematurity was not observed before World War II, but with the availability of supplemental oxygen in the decade following, it rapidly became one of the principal causes of infant blindness in developed countries. By 1960 the use of oxygen had become identified as a risk factor and its administration restricted. The resulting fall in retinopathy of prematurity was accompanied by a rise in infant mortality and hypoxia-related complications. Since then, more sophisticated monitoring and diagnosis have established protocols for oxygen use which aim to balance between hypoxic conditions and problems of retinopathy of prematurity.
Her early work in the plant field was dedicated to the molecular responses of plants to hypoxia and waterlogging, i.e. which genes are switched on by low oxygen levels. She, together with her collaborators, cloned the gene encoding the enzyme alcohol dehydrogenase and identified the regulatory motifs controlling its expression in response to the lack of oxygen. She also was involved in the research showing that all plants contain haemoglobin and that this molecule protects the plant against oxygen deprivation stress 
During this time, there was an increase in molybdenum isotope fractionation. It was temporary, but supports the increase in atmospheric oxygen because molybdenum isotopes require free oxygen to fractionate. Between 2.45 and the second period of oxygenation occurred, it has been called the 'great oxygenation event.' There are many pieces of evidence that support the existence of this event, including red beds appearance (meaning that Fe was being produced and became an important component in soils). The third oxygenation stage approximately is indicated by the disappearance of iron formations. Neodymium isotopic studies suggest that iron formations are usually from continental sources, meaning that dissolved Fe and Fe had to be transported during continental erosion. A rise in atmospheric oxygen prevents Fe transport, so the lack of iron formations may have been due to an increase in oxygen. The fourth oxygenation event, roughly is based on modeled rates of sulfur isotopes from marine carbonate-associated sulfates. An increase (near doubled concentration) of sulfur isotopes, which is suggested by these models, would require an increase in oxygen content of the deep oceans. Between 650 and there were three increases in ocean oxygen levels, this period is the fifth oxygenation stage. One of the reasons indicating this period to be an oxygenation event is the increase in redox-sensitive molybdenum in black shales. The sixth event occurred between 360 and and was identified by models suggesting shifts in the balance of S in sulfates and C in carbonates, which were strongly influenced by an increase in atmospheric oxygen.
If the oxygen content is monitored and the diver identifies a problem with feed gas delivery, it may be possible to manually add gas, or induce triggering of the automatic diluent valve by exhaling to the environment through the nose and thereby artificially reducing the volume of gas in the loop. The forced addition of gas will bring up the oxygen content, but the dive should be terminated as this problem can not be rectified during the dive. This hazard is the strongest argument for oxygen partial pressure monitoring in a CMF SCR..
Patients who are unable to breathe on their own will require positive pressure to move oxygen into their lungs for gaseous exchange to take place. Systems for delivering this vary in complexity (and cost), starting with a basic pocket mask adjunct which can be used by a basically trained first aider to manually deliver artificial respiration with supplemental oxygen delivered through a port in the mask.
Filtered oxygen masks have the ability to prevent exhaled, potentially infectious particles from being released into the surrounding environment. These masks are normally of a closed design such that leaks are minimized and breathing of room air is controlled through a series of one-way valves. Filtration of exhaled breaths is accomplished either by placing a filter on the exhalation port, or through an integral filter that is part of the mask itself. These masks first became popular in the Toronto (Canada) healthcare community during the 2003 SARS Crisis. SARS was identified as being respiratory based and it was determined that conventional oxygen therapy devices were not designed for the containment of exhaled particles. Common practices of having suspected patients wear a surgical mask was confounded by the use of standard oxygen therapy equipment. In 2003, the HiOx oxygen mask was released for sale. The HiOx mask is a closed design mask that allows a filter to be placed on the exhalation port. Several new designs have emerged in the global healthcare community for the containment and filtration of potentially infectious particles. Other designs include the ISO- oxygen mask, the FloMax oxygen mask, and the O-Mask. The use of oxygen masks that are capable of filtering exhaled particles is gradually becoming a recommended practice for pandemic preparation in many jurisdictions.
Oxygen first aid treatment is useful for suspected gas embolism casualties or divers who have made fast ascents or missed decompression stops. Most fully closed-circuit rebreathers can deliver sustained high concentrations of oxygen-rich breathing gas and could be used as an alternative to pure open-circuit oxygen resuscitators. However pure oxygen from an oxygen cylinder through a Non-rebreather mask is the optimal way to deliver oxygen to a decompression illness patient.
The tetraoxygen molecule (O) was first predicted in 1924 by Gilbert N. Lewis, who proposed it to explain why liquid oxygen defied Curie's law. Modern computer simulations indicate that although there are no stable O molecules in liquid oxygen, O molecules do tend to associate in pairs with antiparallel spins, forming transient O units.
The oxygenator was first conceptualized in the 17th century by Robert Hooke and developed into practical extracorporeal oxygenators by French and German experimental physiologists in the 19th century. Bubble oxygenators have no intervening barrier between blood and oxygen, these are called 'direct contact' oxygenators. Membrane oxygenators introduce a gas-permeable membrane between blood and oxygen that decreases the blood trauma of direct-contact oxygenators. Much work since the 1960s focused on overcoming the gas exchange handicap of the membrane barrier, leading to the development of high-performance microporous hollow-fibre oxygenators that eventually replaced direct-contact oxygenators in cardiac theatres.
During this era, oxygenic photosynthesis first evolved, releasing an abundance of oxygen, that first reacted with minerals and afterward was free to react with greenhouse gases of the atmosphere, leaving the Earth's surface free to radiate its energy to space. This is known as the oxygen catastrophe which was to happen later in the Paleoproterozoic from a poisonous buildup of oxygen in the atmosphere, released by these oxygen producing photoautotrophs, which evolved earlier in the Neoarchean.
In most countries, there is no difference in purity in medical oxygen and industrial oxygen, as they are produced by exactly the same methods and manufacturers, but labeled and filled differently. The chief difference between them is that the record-keeping trail is much more extensive for medical oxygen, to more easily identify the exact manufacturing trail of a "lot" or batch of oxygen, in case problems with its purity are discovered. Aviation grade oxygen is similar to medical oxygen, but may have a lower moisture content.
Two functionally unequal subpopulations of neutrophils were identified on the basis of different levels of their reactive oxygen metabolite generation, membrane permeability, activity of enzyme system, and ability to be inactivated. The cells of one subpopulation with high membrane permeability (neutrophil-killers) intensively generate reactive oxygen metabolites and are inactivated in consequence of interaction with the substrate, whereas cells of another subpopulation (neutrophil-cagers) produce reactive oxygen species less intensively, don't adhere to substrate and preserve their activity.
In humans, there are three isoforms of hypoxia-inducible factor-proline dioxygenase. These are PHD1, PHD2 and PHD3. PHD2, in particular, was identified as the most important human oxygen sensors due to its slow reaction with oxygen.
In 1992 she identified a new type of meteorite, the Brachinite. Clayton and Mayeda studied the Achondrite meteorites and identified that variations in the Oxygen-17 isotope within a planet are due to inhomogeneities in the Solar Nebula. They analysed Shergotty meteorites and identified that there could have been a water-rich atmosphere. She found distinct ratios between Oxygen-17, Oxygen-16 and Oxygen-18. She studied the Bocaiuva meteorite, finding that the Eagle Station meteorite were formed due to impact heating.