Link #13: Hydrogen Is The Most Common Element In The Universe


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Link #13: What Are the Most Common Elements Around Us?

question box
question box by Raymond Bryson cc2.0

We discussed in the last post how our Sun contains the majority of the mass of our solar system. This leads us to another crucial and interesting question regarding the universe around us, and our immediate surroundings, and even our bodies. If the mass of the Sun accounts for 99.8 percent of the mass of our whole solar system, what should be the most common element in the whole universe?

The above fact may not provide a certain answer but it does give a good hint toward it. The most common element in the whole universe is the main thing that Sun is made up of — hydrogen.

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Is Hydrogen the Most Common Element in the Universe?

Orion Nebula M42
Orion Nebula M42 by Hubble Heritage cc2.0

Hydrogen is easily the most common element in the universe. You’re probably wondering how this is possible, when things are so different on Earth. However, consider the fact that most compounds, even on Earth, contain hydrogen. The Earth is 70 percent water, right? Water is a combination of two hydrogen atoms and one oxygen atom — or H2O.

More importantly, hydrogen exists freely in space. For example, about 70 percent of our Sun is actually made up of hydrogen atoms. The same story is true for all the other stars in the universe — they contain a lot of hydrogen. Moreover, hydrogen exists on other planets, comets, asteroids and even in free gaseous forms (nebulae).

Approximately 75 percent of the universe as we know it is made up of hydrogen. What about the rest of it? Well, if hydrogen accounts for 75 percent of the universe, the majority of the rest is helium. Helium is the second-most abundant element in the Sun too. The third spot is taken by oxygen.

What Is the Most Common Element on Earth?

Oxygen Symbol
Oxygen symbol. Image credit: Jerome Walker GFDL

Things are slightly different on Earth, though. The most common element in the Earth’s crust is oxygen, at about 46 percent. As mentioned above and as you most probably already knew, Earth is 70 percent water. Even our bodies are 70 percent water. In addition to this, oxygen is a part of most other compounds found on Earth.

The second-most common element in the Earth’s crust, silicon, is related to the amount of sand we have on our planet. The third-most common element is aluminium.

Is Hydrogen the Most Common Element in the Human Body?

Elements of the Human Body
The main elements that compose the human body, by mass percent, are shown from most abundant to least abundant element. The atomic fractions (fractions of atoms) are different due to differing atomic weights. As in water, oxygen contributes the most mass, but hydrogen is the most common atom. By OpenStax College cc3.0

The answer is yes, if you’re counting the number of atoms. But if you consider elements by weight, then hydrogen comes in lower, because it is so light. In terms of weight, the most common element in the human body is oxygen.

The second-most common element (by weight) in our bodies is carbon, because we are carbon-based life forms. This is something that you may have heard of in sci-fi movies. By weight, hydrogen is the third-most abundant element in our body.

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