The first dramatic rise in atmospheric oxygen on Earth, to about a tenth of its present-day value, occurred approximately 2. 5 billion years ago, and that level did not change significantly until the Cambrian era approximately 600 million years ago.

On the simplest level, the oxidizer may itself be an oxidizing element, such as gaseous or liquid oxygen.

Burial of food can preserve it due to a variety of factors: lack of light, lack of oxygen, cool temperatures, pH level, or desiccants in the soil.

A mismatch between oxygen supply and its demand at the cellular level may result in a hypoxic condition.

Studies of miners and astronomers working at 3000 meters and above show improved alveolar pO < sub > 2 </ sub > with full acclimatization, yet the pO < sub > 2 </ sub > level remains equal to or even below the threshold for continuous oxygen therapy for patients with chronic obstructive pulmonary disease ( COPD ).

By increasing the concentration of oxygen in the air, the effects of lower barometric pressure are countered and the level of arterial pO < sub > 2 </ sub > is restored toward normal capacity.

At 4000 m, raising the oxygen concentration level by 5 percent via an oxygen concentrator and an existing ventilation system provides an altitude equivalent of 3000 m, which is much more tolerable for the increasing number of low-landers who work in high altitude.

In a study of astronomers working in Chile at 5050 m, oxygen concentrators increased the level of oxygen concentration by almost 30 percent ( that is, from 21 percent to 27 percent ).

Various factors such as low pH, high CO < sub > 2 </ sub > and high 2, 3 BPG at the level of the tissues favor the taut form, which has low oxygen affinity and releases oxygen in the tissues.

< www. medterms. com / script / main / art. asp? articlekey = 16295 >.</ ref > In addition, increased glycosylation of hemoglobin increases its affinity for oxygen, therefore preventing its release at the tissue and inducing a level of hypoxia in extreme cases.

If un-aerated, the solution level is kept low enough that enough roots are above the solution so they get adequate oxygen.

Erythropoietin is released in response to hypoxia ( low levels of oxygen at tissue level ) in the renal circulation.

In fact, one of the α-ketoglutarate-dependent oxygenases is an O < sub > 2 </ sub > sensor, informing the organism the oxygen level in its environment.

Different studies have come to different conclusions about the amount of oxygen in the atmosphere during different parts of the Mesozoic, with some concluding oxygen levels were lower than the current level ( about 21 %) throughout the Mesozoic, some concluding they were lower in the Triassic and part of the Jurassic but higher in the Cretaceous, and some concluding they were higher throughout most or all of the Triassic, Jurassic and Cretaceous.

* Pasteur point, level of oxygen

The convention had reverted to defining the atomic weight of hydrogen as 1, although at the level of precision of measurements at that time — relative uncertainties of around 1 % — this was numerically equivalent to the later standard of oxygen = 16.

Generally, to supply enough oxygen for respiration, a spacesuit using pure oxygen must have a pressure of about, equal to the partial pressure of oxygen in the Earth's atmosphere at sea level, plus and water vapor pressure, both of which must be subtracted from the alveolar pressure to get alveolar oxygen partial pressure in 100 % oxygen atmospheres, by the alveolar gas equation .< ref >

His study of plants led him to conclude that plants had tubules similar to those he saw in insects like the silk worm ( using his microscope, he probably saw the stomata, through which plants exchange carbon dioxide with oxygen ).

The noble gases, except helium and probably neon, as well as nitrogen, oxygen and hydrogen cause a decrement in mental function, but their effect on psychomotor function ( processes affecting the coordination of sensory or cognitive processes and motor activity ) varies widely.

Newspapers and television news often describe open circuit scuba wrongly as " oxygen " equipment, probably by false analogy to airplane pilots ' oxygen cylinders.

Water probably exists in abundance in other galaxies, too, because its components, hydrogen and oxygen, are among the most abundant elements in the universe.

Water and other volatiles probably comprise much of the internal structures of Uranus and Neptune and the water in the deeper layers may be in the form of ionic water in which the molecules break down into a soup of hydrogen and oxygen ions, and deeper down as superionic water in which the oxygen crystallises but the hydrogen ions float around freely within the oxygen lattice.

In general, " amu " probably does not refer to the old oxygen standard amu, unless the material is older than the 1960's.

The next atmosphere, probably consisting largely of nitrogen ( partly in the form of ammonia ), carbon dioxide, water vapor and other gases, but no free oxygen, was produced by outgassing from volcanism, supplemented by gases produced during the late heavy bombardment of Earth by huge asteroids.

If Theia had been a separate proto-planet, it probably would have had a different oxygen isotopic signature than Earth, as would the ejected mixed material.

Though oxygen was undoubtedly released by photosynthesis well back in Archean times, it could not build up to any significant degree until chemical sinks — unoxidized sulfur and iron — had been filled ; until roughly 2. 3 billion years ago, oxygen was probably only 1 % to 2 % of its current level.

The oxygen buildup was probably due to two factors: a filling of the chemical sinks, and an increase in carbon burial, which sequestered organic compounds that would have otherwise been oxidized by the atmosphere.

Since the whale has limited remaining oxygen supplies at the end of a long dive, it probably has limited abilities to display any normal sound avoidance behavior.

The substitution of oxygen for carbon dioxide in the atmosphere, which occurred in the Proterozoic, caused probably by cyanobacteria in the form of stromatolites, caused changes leading to the evolution of aerobic organisms.

The carbonate carbon and oxygen isotope ratios imply deposition of the carbonates from a gradually evaporating subsurface water body, probably a shallow aquifer meters or tens of meters below the surface.

Heat sources include gravitational energy released by the compression of the core, gravitational energy released by the rejection of light elements ( probably sulfur, oxygen, or silicon ) at the inner core boundary as it grows, latent heat of crystallization at the inner core boundary, and radioactivity of potassium, uranium and thorium.

It is probably related to the extant Anabaena and indicates the presence of significant free oxygen.

Many now agree that both mechanisms are probably present and complementary, or working alongside a mechanism that can detect changes in oxygen and / or carbon dioxide blood saturation.

It is also highly desirable to ensure that the intake gases do not vary significantly in oxygen content over time for safety reasons, as the compressor will probably only be safe for a limited oxygen fraction.

There are probably also physically imposed limits to the size of some organisms ; for instance, insects must be small enough for oxygen to diffuse to all parts of their bodies, flying birds must be light enough to fly, and the length of giraffes ' necks may be limited by the amount of pressure it is possible for their hearts to generate.

Variations in aerator speeds during the latter two months of this study caused increased mixing and increased oxygen demand.

However, unless the airflow is adjusted as well, the flame temperature will decrease because an increased amount of gas is now mixed with the same amount of air, starving the flame of oxygen.

Greater body size implies increased muscle mass and increased oxygen stores.

Because hemoglobin is a darker red when it is not bound to oxygen ( deoxyhemoglobin ), as opposed to the rich red color that it has when bound to oxygen ( oxyhemoglobin ), when seen through the skin it has an increased tendency to reflect blue light back to the eye.

Extraction of an additional electron from iron by oxygen is required to explain both iron's smaller size and observed increased oxidation state, and oxygen's weaker bond.

The binding affinity of hemoglobin for oxygen is increased by the oxygen saturation of the molecule, with the first oxygens bound influencing the shape of the binding sites for the next oxygens, in a way favorable for binding.

This positive cooperative binding is achieved through steric conformational changes of the hemoglobin protein complex as discussed above ; i. e., when one subunit protein in hemoglobin becomes oxygenated, a conformational or structural change in the whole complex is initiated, causing the other subunits to gain an increased affinity for oxygen.

In people acclimated to high altitudes, the concentration of 2, 3-Bisphosphoglycerate ( 2, 3-BPG ) in the blood is increased, which allows these individuals to deliver a larger amount of oxygen to tissues under conditions of lower oxygen tension.

The various hydroponic media available, such as expanded clay and coconut husk, contain more air space than more traditional potting mixes, delivering increased oxygen to the roots, which is important in epiphytic plants such as orchids and bromeliads, whose roots are exposed to the air in nature.

As plants took hold on the continental margins, oxygen levels increased and carbon dioxide dropped, although much less dramatically.

Pasteur showed that by bubbling oxygen into the yeast broth, cell growth could be increased, but fermentation was inhibited – an observation later called the " Pasteur effect ".

Carbon dioxide diffuses into the surrounding water due to its high solubility, while oxygen diffuses into bubbles as the concentration within the bubble has been reduced by respiration, and nitrogen also diffuses out as its tension has been increased.

Adaptations that enable the cheetah to run as fast as it does include large nostrils that allow for increased oxygen intake, and an enlarged heart and lungs that work together to circulate oxygen efficiently.

found cerebral blood flow is increased, cerebral vascular resistance is decreased, arteriovenous oxygen difference is decreased, and oxygen consumption is unchanged.