Composition of the Universe – Element Abundance

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Composition of the Universe
Around 99% of the atoms in the universe are hydrogen and helium, accounting for about 75% and 23% of its mass, respectively.

There are two ways of expressing the composition of the universe in terms of element abundance. The first is the abundance of atoms of each element, while the second is the mass percent of each element. These two methods give very different values. For example, the percent of atoms in water (H2O) that are hydrogen and oxygen are 66.6% H and 33.3% O, while the mass percent is 11% H and 89% O.

The Most Abundant Element in the Universe

Hydrogen is by far the most abundant element, accounting for about 92% of the atoms in the universe. The next-most abundant element is helium, accounting for 7.1% of the universe’s atoms. In general, the universe contains more atoms of elements with lighter atomic masses than atoms of heavier elements.

Composition of the Universe – Atoms of Elements

In terms of number of atoms, here are the 10 most abundant elements in the universe:

Atomic NumberSymbolElementPercent of Atoms
in Universe
1HHydrogen92%
2HeHelium7.1%
8OOxygen0.1%
6CCarbon0.06%
10NNitrogen0.015%
7NeNeon0.012%
14SiSilicon0.005%
12MgMagnesium0.005%
26FeIron0.004%
16SSulfur0.002%

In other words, these ten elements account for about 99.3% of all the atoms in the universe.

Table of Element Abundance of the Universe – Mass Percent

More commonly, a table of abundance describes elements in terms of mass percent.

Combining what we know about the composition of the Milky Way with what we see in other galaxies gives us an estimate of the element abundance of the universe. The 83 most abundant elements all have at least one stable isotope. Next, there are radioactive elements that exist in nature, but only occur in trace amounts because of radioactive decay. The superheavy elements are only synthesized in labs.

Atomic NumberSymbolNameRelative
Abundance		Abundance in Universe
(by mass percent)
1HHydrogen175
2HeHelium223
8OOxygen31
6CCarbon40.5
10NeNeon50.13
26FeIron60.11
7NNitrogen70.10
14SiSilicon80.07
12MgMagnesium90.06
16SSulfur100.05
18ArArgon110.02
20CaCalcium120.007
28NiNickel130.006
13AlAluminum140.005
11NaSodium150.002
24CrChromium160.015
25MnManganese178×10-4
15PPhosphorus187×10-4
19KPotassium193×10-4
22TiTitanium203×10-4
27CoCobalt213×10-4
17ClChlorine221×10-4
23VVanadium231×10-4
9FFluorine244×10-5
30ZnZinc253×10-5
32GeGermanium262×10-5
29CuCopper276×10-6
40ZrZirconium285×10-6
36KrKrypton294×10-6
38SrStrontium304×10-6
21ScScandium313×10-6
34SeSelenium323×10-6
31GaGallium331×10-6
37RbRubidium341×10-6
54XeXenon351×10-6
56BaBarium361×10-6
58CeCerium371×10-6
60NdNeodymium381×10-6
82PbLead391×10-6
52TeTellurium409×10-7
33AsArsenic418×10-7
35BrBromine427×10-7
39YYttrium437×10-7
3LiLithium446×10-7
42MoMolybdenum455×10-7
62SmSamarium465×10-7
78PtPlatinum475×10-7
44RuRuthenium484×10-7
50SnTin494×10-7
76OsOsmium503×10-7
41NbNiobium512×10-7
46PdPalladium522×10-7
48CdCadmium532×10-7
57LaLanthanum542×10-7
59PrPraseodymium552×10-7
64GdGadolinium562×10-7
66DyDysprosium572×10-7
68ErErbium582×10-7
70YbYtterbium592×10-7
77IrIridium602×10-7
4BeBeryllium611×10-7
5BBoron621×10-7
53IIodine631×10-7
80HgMercury641×10-7
55CsCesium658×10-8
72HfHafnium667×10-8
83BiBismuth677×10-8
45RhRhodium686×10-8
47AgSilver696×10-8
79AuGold706×10-8
63EuEuropium715×10-8
65TbTerbium725×10-8
67HoHolmium735×10-8
74WTungsten745×10-8
81TlThallium755×10-8
51SbAntimony764×10-8
90ThThorium774×10-8
49InIndium783×10-8
75ReRhenium792×10-8
92UUranium802×10-8
69TmThulium811×10-8
71LuLutetium821×10-8
73TaTantalum838×10-9
89AcActinium–trace (radioactive)
85AtAstatine–trace (radioactive)
87FrFrancium–trace (radioactive)
93NpNeptunium–trace (radioactive)
94PuPlutonium–trace (radioactive)
84PoPolonium–trace (radioactive)
61PmPromethium–trace (radioactive)
91PaProtactinium–trace (radioactive)
88RaRadium–trace (radioactive)
86RnRadon–trace (radioactive)
43TcTechnetium–trace (radioactive)
95AmAmericium–0 (synthetic)
96CmCurium–0 (synthetic)
97BkBerkelium–0 (synthetic)
98CfCalifornium–0 (synthetic)
99EsEinsteinium–0 (synthetic)
100FmFermium–0 (synthetic)
101MdMendelevium–0 (synthetic)
102NoNobelium–0 (synthetic)
103LrLawrencium–0 (synthetic)
104RfRutherfordium–0 (synthetic)
105DbDubnium–0 (synthetic)
106SgSeaborgium–0 (synthetic)
107BhBohrium–0 (synthetic)
108HsHassium–0 (synthetic)
109MtMeitnerium–0 (synthetic)
110DsDarmstadtium–0 (synthetic)
111RgRoentgenium–0 (synthetic)
112CnCopernicium–0 (synthetic)
113NhNihonium–0 (synthetic)
114FlFlerovium–0 (synthetic)
115McMoscovium–0 (synthetic)
116LvLivermorium–0 (synthetic)
117TsTennessine–0 (synthetic)
118OgOganesson–0 (synthetic)

Even-Numbered Elements Are More Abundant

Note that elements with even atomic numbers, such as helium (2) and oxygen (8), are more abundant than odd-numbered elements on either side of it on the periodic table, such as lithium (3) and nitrogen (7). This phenomenon is called the Oddo-Harkins rule. The easiest explanation for this pattern is that many element form via fusion in stars using helium as a building block. Also, even atomic numbers lead to proton pair formation in the atomic nucleus. This parity increases atomic stability because the spin of one proton offsets the opposite spin of its partner.

The big exceptions to the Oddo-Harkins rule are hydrogen (1) and beryllium (4). Hydrogen is much more abundant than the other elements because it formed during the Big Bang. As the universe ages, hydrogen fuses into helium. Eventually, helium becomes more abundant than hydrogen. One explanation for the low abundance of beryllium is that it has only one stable isotope, so it changes into other elements via radioactive decay. Boron (3) and lithium (5) each have two stable isotopes.

How Do We Know the Composition of the Universe?

There is some guesswork involved in estimating the element composition of the universe. Scientists use spectroscopy to measure the element signatures of elements in stars and nebulae. We have a pretty good idea of the composition of the Earth and the other planets in the solar system. Observations of distant galaxies are a glimpse into their past, so researchers compare that data with what we know about the Milky Way and nearby galaxies. Ultimately, our understanding of the the composition of the universe assumes physical laws and composition are constant and our understanding of nucleosynthesis (how elements are made) is accurate. So, scientists know what elements were in the earlier universe, what they are now, and how the composition changes over time.

Dark Matter and Dark Energy

The elements only make up about 4.6% of the universe’s energy. Scientists think about 68% of the universe consists of dark energy and about 27% of dark matter. But, these are forms of energy and matter we haven’t been able to observe and measure directly.

References

  • Arnett, David (1996). Supernovae and Nucleosynthesis (1st ed.). Princeton, New Jersey: Princeton University Press. ISBN 0-691-01147-8.
  • Cameron, A. G. W. (1973). “Abundances of the elements in the solar system”. Space Science Reviews. 15 (1): 121. doi:10.1007/BF00172440
  • Suess, Hans; Urey, Harold (1956). “Abundances of the Elements”. Reviews of Modern Physics. 28 (1): 53. doi:10.1103/RevModPhys.28.53
  • Trimble, Virginia (1996). “The Origin and Evolution of the Chemical Elements”. In Malkan, Matthew A.; Zuckerman, Ben (eds.). The Origin and Evolution of the Universe. Sudbury, MA: Jones and Bartlett Publishers. ISBN 0-7637-0030-4.
  • Vangioni-Flam, Elisabeth; Cassé, Michel (2012). Spite, Monique (ed.). Galaxy Evolution: Connecting the Distant Universe with the Local Fossil Record. Springer Science & Business Media. ISBN 978-9401142137.