Oxygen is a chemical element in the periodic table. It has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe, usually covalently bonded with other elements. Unbound oxygen (usually called molecular oxygen, O2, a diatomic molecule) first appeared on Earth during the Paleoproterozoic era (between 2500 million years ago and 1600 million years ago) and as a product of the metabolic action of early anaerobes (archaea and bacteria). The presence of free oxygen ...

Including:

• Oxygen - Characteristics
• Oxygen - Applications
• Oxygen - History
• Oxygen - Occurrence
• Oxygen - Compounds
• Oxygen - Isotopes
• Oxygen - Precautions

Read more here: » Oxygen: Encyclopedia - Oxygen

See also:

Oxygen, Oxygen - Characteristics, Oxygen - Applications, Oxygen - History, Oxygen - Occurrence, Oxygen - Compounds, Oxygen - Isotopes, Oxygen - Precautions

Read more here: » Oxygen: Encyclopedia II - Oxygen - Precautions

Liquid oxygen finds use as an oxidizer in rocket propulsion. Oxygen is essential to respiration, so oxygen supplementation has found use in medicine (as oxygen therapy). People who climb mountains or fly in airplanes sometimes have supplemental oxygen supplies (as air). Oxygen is used in welding (such as the oxyacetylene torch), and in the making of steel and methanol. Oxygen presents two absorption bands centered in the wavelengths 687 and 760 nanometers. Some scientists have proposed to use the measurement of the radiance coming fro ...

See also:

Oxygen, Oxygen - Characteristics, Oxygen - Applications, Oxygen - History, Oxygen - Occurrence, Oxygen - Compounds, Oxygen - Isotopes, Oxygen - Precautions

Read more here: » Oxygen: Encyclopedia II - Oxygen - Applications

Drowning is death caused by the filling of the lungs by a fluid, usually water, rendering breathing impossible and leading to death due to asphyxia. Near drowning is initial survival of a drowning accident, and can lead to serious secondary complications including death later on; cases of near drowning therefore also require attention by medical professionals. Secondary drowning is death due to chemical and biological changes in the lungs after a near drowning incident or exposure to chemicals. In many countries, drownin ...

Including:

• Drowning - Occurrences
• Drowning - The drowning process
• Drowning - Common situations leading to drowning
• Drowning - Initial Reactions to Submersion
• Drowning - Initial Oxygen Starvation
• Drowning - Water entering the upper airways
• Drowning - Unconsciousness due to Oxygen Starvation
• Drowning - Secondary drowning
• Drowning - Cardiac Arrest and Death
• Drowning - Rescue and Treatment
• Drowning - Prevention

Read more here: » Drowning: Encyclopedia - Drowning

An alkane in organic chemistry is a saturated hydrocarbon without cycles, that is, an acyclic hydrocarbon in which the molecule has the maximum possible number of hydrogen atoms and so has no double bonds. Alkanes are also often known as paraffins, or collectively as the paraffin series; these terms, however, are also used to apply only to alkanes whose carbon atoms form a single, unbranched chain; when this is done, branched-chain alkanes are called isoparaffins. Alkanes are aliphatic compounds. The general formu ...

Including:

• Alkane - Isomerism
• Alkane - Nomenclature of alkanes
• Alkane - Alkanes with unbranched carbon chains
• Alkane - Alkanes with branched carbon chains
• Alkane - Trivial names
• Alkane - Occurrence
• Alkane - Purification and use
• Alkane - Preparation
• Alkane - Molecular geometry
• Alkane - Bond lengths and bond angles
• Alkane - Conformation
• Alkane - Properties
• Alkane - Physical properties
• Alkane - Chemical properties
• Alkane - Thermochemistry
• Alkane - Spectroscopic properties
• Alkane - Reactions
• Alkane - Reactions with oxygen
• Alkane - Reactions with halogens
• Alkane - Cracking and reforming
• Alkane - Other reactions
• Alkane - Hazards
• Alkane - Alkanes in nature
• Alkane - Bacteria and archaea
• Alkane - Fungi and plants
• Alkane - Animals
• Alkane - Ecological relations

Read more here: » Alkane: Encyclopedia - Alkane

An anoxic event occurs when the Earth's oceans become completely depleted of O2 below the surface levels. Anoxic event - Occurrence. Anoxic events occur only during periods of very warm climate characterised by high levels of CO2, usually above 1800 ppmv, and mean surface temperatures of around 22 ° C (Quaternary levels are 280 ppmv and 13 ° C). Thus, anoxic events have been concentrated in the Paleogene, Cretaceous and Jurassic, when numoerous ones have been documented ...

Including:

• Anoxic event - Occurrence
• Anoxic event - Major anoxic events in the Cretaceous
• Anoxic event - Mechanism
• Anoxic event - Consequences

Read more here: » Anoxic event: Encyclopedia - Anoxic event

Argon is a chemical element in the periodic table. It has the symbol Ar and atomic number 18. The third noble gas, in group 18, argon makes up about 1% of the Earth's atmosphere, making it the most common noble gas on Earth. Argon - Notable characteristics. Argon is 2.5 times as soluble in water as nitrogen which is approximately the same solubility as oxygen. This highly stable chemical element is colorless and odorless in both its liquid and gaseous forms. There are few known true che ...

Including:

• Argon - Notable characteristics
• Argon - Applications
• Argon - History
• Argon - Occurrence
• Argon - Compounds
• Argon - Isotopes

Read more here: » Argon: Encyclopedia - Argon

Chromium is a chemical element in the periodic table that has the symbol Cr and atomic number 24. Chromium - Notable characteristics. Chromium is a steel-gray, lustrous, hard metal that takes a high polish, melts with difficulty, and tarnishes. The most common oxidation states of chromium are +2, +3, and +6, with +3 being the most stable. +4 and +5 are rare. Chromium compounds of oxidation state 6 are powerful oxidants. Chromium(0) is unstable in oxygen, immediately producing a thin oxi ...

Including:

• Chromium - Notable characteristics
• Chromium - Applications
• Chromium - History
• Chromium - Biological role
• Chromium - Occurrence
• Chromium - Compounds
• Chromium - Isotopes
• Chromium - Chromium and the quintuple bond
• Chromium - Precautions

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Cryolite (Na3AlF6, sodium aluminium fluoride) is an uncommon mineral of very limited natural distribution. It is mostly identified with the once large deposit at Ivigtût on the west coast of Greenland. It was historically used as an ore of aluminium and later in the electroytic processing of the aluminium rich oxide ore, bauxite, which is a combination of aluminium oxide minerals such as gibbsite, boehmite and diaspore. The difficulty of removing aluminium from oxygen in the oxide ores was overcome by the ...

Read more here: » Cryolite: Encyclopedia - Cryolite

Zircon is a mineral belonging to the group of nesosilicates. Its chemical formula is ZrSiO4. Hafnium is almost always present ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal class. The natural color of zircon varies between colorless, yellow-golden, red, brown or green. Colorless specimens that show gem quality are a popular substitute for diamond; these specimens are also know ...

Including:

• Zircon - Properties
• Zircon - Uses
• Zircon - Zircons and the age of Earth

Read more here: » Zircon: Encyclopedia - Zircon

Apollo 13 was an American space mission, part of the Apollo program. It was intended to be the third mission to land on the Moon, but instead is famous for the critical malfunction it suffered and its difficult but successful return home. Apollo 13 - Crew. Jim Lovell (flew on Gemini 7, Gemini 12, Apollo 8 & Apollo 13), commander Jack Swigert (flew on Apollo 13), command module pilot Fred Haise (flew on Apollo 13), lunar module pilot ...

Including:

• Apollo 13 - Crew
• Apollo 13 - Backup crew
• Apollo 13 - Support crew
• Apollo 13 - Mission parameters
• Apollo 13 - Oxygen tank explosion
• Apollo 13 - Closest approach to Moon
• Apollo 13 - Quote
• Apollo 13 - Mission highlights
• Apollo 13 - Problem
• Apollo 13 - Cause of the accident
• Apollo 13 - Mission notes
• Apollo 13 - Insignia
• Apollo 13 - Relics
• Apollo 13 - Dramatization
• Apollo 13 - Games

Read more here: » Apollo 13: Encyclopedia - Apollo 13

Barium is a toxic chemical element in the periodic table that has the symbol Ba and atomic number 56. A soft silvery metallic element, barium is an alkaline earth metal and melts at a very high temperature. Its oxide is called baryta and it is primarily found in the mineral barite but is never found in its pure form due to its reactivity with air. Compounds of this metal are used in small quantities in paints and in glassmaking. Barium - Notable characteristics. Barium is a metallic ele ...

Including:

• Barium - Notable characteristics
• Barium - Applications
• Barium - History
• Barium - Occurrence
• Barium - Compounds
• Barium - Isotopes
• Barium - Precautions

Read more here: » Barium: Encyclopedia - Barium

The mechanism by which anoxic events occur is still very poorly understood. It is believed that, with the oceans very warm, and, in the complete absence of polar ice caps they covered large areas that are now dry land. Because of the warmth, much less oxygen could be dissolved in the water, and the small amount was largely used up by marine animals such as corals at very shallow depths, thus preventing oxygen from penetrating to ...

See also:

Anoxic event, Anoxic event - Occurrence, Anoxic event - Major anoxic events in the Cretaceous, Anoxic event - Mechanism, Anoxic event - Consequences

Read more here: » Anoxic event: Encyclopedia II - Anoxic event - Mechanism

Anoxic events have had many important consequences. It is believed that they have been responsible for mass extinctions of marine organisms both in the Paleozoic and Mesozoic. This is natural when one considers that most marine organisms cannot adapt to an ocean where oxygen can - at best - reach only the surface layers. Another, much more useful, consequence of anoxic events has been the fact that the anoxia of so many Mesozoic oceans has produced most of the world's petroleum and natural gas deposits. During an anoxic event, ...

See also:

Anoxic event, Anoxic event - Occurrence, Anoxic event - Major anoxic events in the Cretaceous, Anoxic event - Mechanism, Anoxic event - Consequences

Read more here: » Anoxic event: Encyclopedia II - Anoxic event - Consequences

Although alkanes occur in nature in various way, they do not rank biologically among the essential materials. Cycloalkanes with 14 to 18 carbon atoms occur in musk, extracted from deer of the family Moschidae. All further information refers to acyclic alkanes. Alkane - Bacteria and archaea. Certain types of bacteria can metabolise alkanes: they prefer even-numbered carbon chains as they are ...

See also:

Alkane, Alkane - Isomerism, Alkane - Nomenclature of alkanes, Alkane - Alkanes with unbranched carbon chains, Alkane - Alkanes with branched carbon chains, Alkane - Trivial names, Alkane - Occurrence, Alkane - Purification and use, Alkane - Preparation, Alkane - Molecular geometry, Alkane - Bond lengths and bond angles, Alkane - Conformation, Alkane - Properties, Alkane - Physical properties, Alkane - Chemical properties, Alkane - Thermochemistry, Alkane - Spectroscopic properties, Alkane - Reactions, Alkane - Reactions with oxygen, Alkane - Reactions with halogens, Alkane - Cracking and reforming, Alkane - Other reactions, Alkane - Hazards, Alkane - Alkanes in nature, Alkane - Bacteria and archaea, Alkane - Fungi and plants, Alkane - Animals, Alkane - Ecological relations

Read more here: » Alkane: Encyclopedia II - Alkane - Alkanes in nature

Alkanes occur both on Earth and in the solar system, however only the first hundred or so, and even then mostly only in traces. The light hydrocarbons, especially methane and ethane are of great importance for other heavenly bodies: they are found, for example, both in the tail of the comet Hyakutake and in some meteorites such as carbonaceous chondrites. They also form an important portion of the atmospheres of the outer gas planets Jupiter, Saturn, Uranus and Neptune. On Titan, the satellite of Saturn, it is believed that there were once large oceans of these and longer chain alkanes: smaller seas of liquid eth ...

See also:

Alkane, Alkane - Isomerism, Alkane - Nomenclature of alkanes, Alkane - Alkanes with unbranched carbon chains, Alkane - Alkanes with branched carbon chains, Alkane - Trivial names, Alkane - Occurrence, Alkane - Purification and use, Alkane - Preparation, Alkane - Molecular geometry, Alkane - Bond lengths and bond angles, Alkane - Conformation, Alkane - Properties, Alkane - Physical properties, Alkane - Chemical properties, Alkane - Thermochemistry, Alkane - Spectroscopic properties, Alkane - Reactions, Alkane - Reactions with oxygen, Alkane - Reactions with halogens, Alkane - Cracking and reforming, Alkane - Other reactions, Alkane - Hazards, Alkane - Alkanes in nature, Alkane - Bacteria and archaea, Alkane - Fungi and plants, Alkane - Animals, Alkane - Ecological relations

Read more here: » Alkane: Encyclopedia II - Alkane - Occurrence

Drowning - Common situations leading to drowning. Most drownings occur in water, drownings in other fluids are comparatively rare and often industrial accidents. Surveys suggest that 90% of drownings occur in freshwater (rivers and lakes) rather than in the ocean. Well known mechanisms by which a person drowns can be categorized as follows: Physically hindered in the attempt to extricate self (e.g. lack of consciousness, injury, being trapped, or hampered by clothing) Physiological in ...

See also:

Drowning, Drowning - Occurrences, Drowning - The drowning process, Drowning - Common situations leading to drowning, Drowning - Initial Reactions to Submersion, Drowning - Initial Oxygen Starvation, Drowning - Water entering the upper airways, Drowning - Unconsciousness due to Oxygen Starvation, Drowning - Secondary drowning, Drowning - Cardiac Arrest and Death, Drowning - Rescue and Treatment, Drowning - Prevention

Read more here: » Drowning: Encyclopedia II - Drowning - The drowning process

Anoxic events occur only during periods of very warm climate characterised by high levels of CO2, usually above 1800 ppmv, and mean surface temperatures of around 22 ° C (Quaternary levels are 280 ppmv and 13 ° C). Thus, anoxic events have been concentrated in the Paleogene, Cretaceous and Jurassic, when numoerous ones have been documented, but earlier ones are known from the late Triassic, Devonian and Ordovician. Major anoxic events occurred between 183 and 180 million years ago, and many times in the period from ...

See also:

Anoxic event, Anoxic event - Occurrence, Anoxic event - Major anoxic events in the Cretaceous, Anoxic event - Mechanism, Anoxic event - Consequences

Read more here: » Anoxic event: Encyclopedia II - Anoxic event - Occurrence

Thiophenes are prepared by the reaction of 1,4-diketones with sulfiding reagents such as Lawesson's reagent or P4S10. In fact, reflecting their high stabilities, thiophenes arise from many reactions involving sulfur sources and hydrocarbons, especially unsaturated ones. Thiophene and its derivatives occur in petroleum, sometimes in concentrations up to 1-3 percent. The thiophenic content of liquids from oil/coal is removed via the hydrodesulfurization (HDS) process. In HDS, the liquid or gaseous feed is passed ov ...

See also:

Thiophene, Thiophene - Properties, Thiophene - Uses, Thiophene - Synthesis and Occurrence

Read more here: » Thiophene: Encyclopedia II - Thiophene - Synthesis and Occurrence

Many pools and designated bathing areas either have either lifeguards, a pool safety camera system for local or remote monitoring, or computer aided drowning detection. However, bystanders play an important role in drowning detection and either intervention or the notification of authorities by phone or alarm. No person should attempt a rescue that is beyond their ability or level of training! If a drowning occurs or a swimmer becomes missing, bystanders should immediately call for help. The lifeguard should be called if present. If not, Emergency medical services and Pa ...

See also:

Drowning, Drowning - Occurrences, Drowning - The drowning process, Drowning - Common situations leading to drowning, Drowning - Initial Reactions to Submersion, Drowning - Initial Oxygen Starvation, Drowning - Water entering the upper airways, Drowning - Unconsciousness due to Oxygen Starvation, Drowning - Secondary drowning, Drowning - Cardiac Arrest and Death, Drowning - Rescue and Treatment, Drowning - Prevention

Read more here: » Drowning: Encyclopedia II - Drowning - Rescue and Treatment