Oxygen is the gas that keeps us alive, but there is far more to it than breathing. It makes up most of the rocks under our feet, turns blue and magnetic when it is cold enough, and helps launch rockets into space. Here are 12 facts about oxygen.
1Its symbol is O and its atomic number is 8.
Every oxygen atom has 8 protons. In the air, oxygen atoms pair up into molecules of two, which is why the gas we breathe is written O2.
2It is the third most common element in the universe.
Only hydrogen and helium are more plentiful. Oxygen is made inside large stars and scattered across space when they explode.
3It is the most common element in the Earth’s crust.
About 46% of the Earth’s crust by weight is oxygen, locked up in rocks and minerals such as quartz and silicates. It also makes up about 65% of the weight of the human body, mostly in the form of water.
4It makes up about 21% of the air.
Most of the air is nitrogen, at about 78%. Oxygen is the second most common gas, and the remaining 1% is mostly argon.
5Two men discovered it at almost the same time.
The Swedish chemist Carl Wilhelm Scheele made oxygen in the early 1770s, but his work was not published until 1777. The English chemist Joseph Priestley discovered it independently in 1774 and published first, so both are given credit.
6Its name is based on a mistake.
The French chemist Antoine Lavoisier named it oxygène, from Greek words meaning “acid maker”, because he wrongly believed that all acids contained oxygen.
7Liquid oxygen is pale blue and magnetic.
Oxygen turns into a liquid at -183°C. Liquid oxygen is a pale sky blue, and it is attracted to magnets: poured between the poles of a strong magnet, it sticks there.
8The early Earth had almost no oxygen in the air.
For its first two billion years, the Earth’s atmosphere had almost no free oxygen. Around 2.4 billion years ago, tiny ocean organisms called cyanobacteria had made so much of it through photosynthesis that it began to build up, an event called the Great Oxidation Event.
9The ocean makes about half of the world’s oxygen.
Scientists estimate that roughly half of the oxygen produced on Earth comes from the ocean, mostly from microscopic plants called phytoplankton.
10The ozone layer is made of oxygen.
Ozone is a form of oxygen with three atoms instead of two. A layer of it high in the atmosphere absorbs most of the Sun’s harmful ultraviolet light.
11Fire cannot burn without it.
Fire needs heat, fuel and oxygen. Take away any one of these and the fire goes out, which is how fire blankets and some extinguishers work, by cutting off the oxygen.
12Too much oxygen can be harmful.
Breathing high levels of oxygen under pressure can affect the lungs and nervous system. That is why scuba divers using oxygen-rich mixes such as nitrox must stay above a set depth, and why pure oxygen is only safe at very shallow depths.
FAQs about oxygen
Is oxygen O or O2?
Both. O is a single oxygen atom. The oxygen gas we breathe is made of molecules of two atoms joined together, written O2.
Who discovered oxygen?
Carl Wilhelm Scheele and Joseph Priestley discovered it separately in the 1770s. Antoine Lavoisier explained what it was and gave it its name.
Do rockets use oxygen?
Yes. There is no air in space, so rockets carry their own oxygen, usually as a liquid, to burn their fuel. The Saturn V that took astronauts to the Moon used liquid oxygen.
Sources and further reading
Explore more: facts about chlorine.
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