Oxygen

[[Image:O2pict.gif|thumb|Diagram of an O<sub>2</sub> molecule]]{{Chemistry}}
'''Oxygen''' is an [[element]] that forms a diatomic gas (O<sub>2</sub>) under [[Earth]]'s surface conditions. It also readily forms a triatomic [[molecule]], known as ozone (O<sub>3</sub>), under some conditions, such as electrical discharges. Ozone is more stable in the upper atmosphere and forms a barrier to [[ultraviolet]] energy, the [[ozone layer]], which is very important to current [[life]]-forms on the planet.

O<sub>2</sub> is a highly reactive chemical, so much so that most [[Chemistry|chemical]] reactions are classed as "oxidation" or "reduction" reactions depending on the relative exchange of electrons involved. The process of oxidation is fascinating, with its results varying from forming a protective, non-oxidizing surface coating on [[aluminum]], to slowly destroying artifacts made of [[iron]] ("rust"), to rapid processes we call combustion, which release large amounts of chemical [[energy]] in short periods of time.

Oxygen in its pure form is a useful industrial and medical commodity, and is often cooled and compressed into its liquid state for storage and transportation.

==Shaping the earth==
Earth's atmosphere is roughly 21% oxygen, which is created and replenished by [[plant]]s using [[photosynthesis]] to capture [[energy]] from the [[sun]]. Most [[animal]] life depends on acquiring it via respiration, in order to use it in chemical reactions to [[metabolism|obtain energy from food]].

Oxygen-deprived regions are called "anoxic". Anaerobic [[bacteria]] are those which can survive only in environments in which there is no oxygen, and for which oxygen is toxic. It has been hypothesized that in order for [[Origin of life|life to form]] on earth, the entire atmosphere would have to be anaerobic, as oxygen would have caused the breakup of primitive organic chemicals as they first began to form. This is highly likely, since oxygen is a highly reactive element. The only reason we now have an atmosphere that is roughly one-fifth oxygen is the constant production of it as a waste product of photosynthesis. Note that when plants first [[Evolution|evolved]] this process and started pumping O<sub>2</sub> into the atmosphere, there was a mini-extinction event, known as the "{{wpl|Great Oxygenation Event||",}} as it poisoned organisms that could not tolerate it.

Oxygen caused exposed iron to rust as plants started to release it in photosynthesis.

Additionally, oxygen is the most abundant element in Earth's crust and the second most abundant overall next to iron, being around 46.6% of the mass of Earth's crust. It primarily exists in the form of common silicate minerals such as quartz and feldspar, as well as in oxides such as hematite.<ref>[https://www.ebsco.com/research-starters/chemistry/oxygen-o Oxygen], ''EBSCO''</ref>

==Ozone==
[[File:ozonerot.gif|thumb|200px|right|ozone]]
'''Ozone''' (O<sub>3</sub>) or "trioxygen", is a triatomic molecule consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the usual diatomic allotrope, O<sub>2</sub>. 

Ozone in the lower atmosphere is an air [[pollution|pollutant]] with harmful effects on the respiratory systems of animals and will burn sensitive plants. The [[ozone layer]] in the upper atmosphere is beneficial, preventing potentially damaging ultraviolet [[light]] from reaching the [[Earth]]'s surface. Ozone is present in low concentrations throughout the Earth's atmosphere and is the key component of most atmospheric [[chemistry]].

Atmospheric ozone levels are one measure of air quality. In the 1950s, a Stage 1 Smog Alert occurred when the ozone level rose to 0.5 parts per million, and a Stage 2 Smog Alert was declared at 1 part per million of ozone. (Today, 0.5 ppm of ozone would qualify as a Stage 3 Smog Alert.)<ref>http://latimesblogs.latimes.com/thedailymirror/2007/06/smog-alert.html</ref>

People in Victorian [[Britain]] would go to &mdash; indeed, were advised by physicians to go to &mdash; the seaside to "take the ozone". Fortunately, there's no more in sea air than there is anywhere else, or they'd have been coughing up blood. That characteristic seaside smell is dimethyl sulfide (C<sub>2</sub>H<sub>6</sub>S) derived from rotting seaweed.<ref>[http://www.telegraph.co.uk/news/uknews/1541342/Secrets-of-bracing-sea-air-bottled-by-scientists.html The Telegraph, 2 February 2007]</ref>

If you're [[Gwyneth Paltrow]], you might go on a podcast to lament how you feel misunderstood and judged for your lifestyle choices, such as the one where you get ozone blown up your ass.<ref>https://eu.usatoday.com/story/entertainment/celebrities/2023/03/14/gwyneth-paltrow-reveals-rectal-ozone-therapy/11474050002/</ref> There are, however, no medically validated therapeutic indications for rectal ozone therapy.

==Oxygen ratio cycle==
[[File:Planktonic foraminifera.jpg|thumb|right|165px|Shells of foraminifera, which can be used to determine the climate during the time that they lived.]]
There are two common isotopes of oxygen: oxygen-16 and oxygen-18. Oxygen-18, or "heavy oxygen", has two extra neutrons compared to oxygen-16, and water that contains heavy oxygen doesn't evaporate as easily as water that contains only light oxygen. Thus, the ratio of oxygen-18 to oxygen-16 is a good indicator of the water's temperature, with more heavy oxygen indicating a hotter climate.<ref>[https://earthobservatory.nasa.gov/features/Paleoclimatology_OxygenBalance Paleoclimatology: The Oxygen Balance], Holli Riebeek, 6 May 2005</ref> There are a few ways to find the oxygen ratios of past climates. One way is by taking ice cores in glaciers and looking at how the oxygen ratio changed over time. Another way is to look at fossils of foraminifera, tiny planktonic creatures that build their shells using oxygen from the surrounding water. By using these methods, we can determine how the climate has changed in the past, and it also provides convincing evidence that the climate was relatively stable for the past ten thousand years, but has significantly warmed in the past 200 or so.<ref>[https://www.cambridge.org/core/journals/the-paleontological-society-papers/article/abs/oxygen-isotopes-in-foraminifera-overview-and-historical-review/CD34EFBFFB6AC31DB85A61BB7E6FA64F Oxygen Isotopes in Foraminifera: Overview and Historical Review], Paul N. Pearson, ''Cambridge University Press'' 21 July 2017</ref>

==Health and danger==
Just as with many other chemicals necessary for the continuance of healthy human life, [[Pseudoscience|some]] [[Water woo|people]] [[Food woo|are]] [[Diet woo|tempted]] [[Nature woo|to]] [[Science woo|believe that]] [[Bullshit|"more is better"]]. Hence the existence of "[[oxygen therapy]]". "More is better" is a harmless belief in the case of [[Vitamin C]], as excess intake (except in such grotesque proportions as to cause acidosis) will simply be flushed out, but in the case of oxygen, not so much. Oxygen, at high partial pressures, is a powerful cellular toxin due to the same strong reactivity that makes it such a vital chemical at lower partial pressures. (As toxicologists say, ''[[the dose makes the poison]]''.)

Oxygen at high temperatures is extremely corrosive, causing fires with most substances. While it isn't flammable itself, oxygen in high concentrations makes many other things burn easily, even items which aren't normally burnable. The Apollo I fire occurred because the test on the pad was done in pure oxygen at sea level pressure (the Apollo missions were flown at 5-6psi; at that pressure, pure oxygen is no more dangerous than regular air).

A 2015 research paper found an association between increased lung [[cancer]] rates and higher levels of atmospheric oxygen associated with populations living at lower altitudes.<ref>[https://www.sciencenews.org/article/more-oxygen-may-lead-more-tumors?mode=magazine&context=189691 More oxygen may lead to more tumors: Lung cancer risk drops at higher elevations where the air is thinner] (''Science News'' summary)</ref><ref>[https://peerj.com/articles/705/ Lung cancer incidence decreases with elevation: evidence for oxygen as an inhaled carcinogen] by K. P. Simeonov and D. S. Himmelstein, ''PeerJ''. Vol. 2, January 13, 2015, p. e705. doi:10.7717/peerj.705</ref> Of course, [[correlation does not imply causation]], but it does given one pause, since oxygen is highly chemically reactive.

==See also==
*[[Carbon]]
*[[Helium]]
*[[Hydrogen]]
*[[Hyperbaric oxygen therapy]]
*[[Oxygen therapy]]
*[[Water woo#Oxygenated water|Oxygenated water]]

==References==
{{reflist|2|80%}}

==Notes==
{{reflist|group=note}}

[[Category:Chemicals]]
[[Category:Climatology]]
[[Category:Elements]]

Categories: Chemicals, Climatology, Elements